Engine Cooling and HVAC - Overview BMW M3 E46

Scheme 49

At operating temperature, an automotive engine produces excess heat. Heat is a by-product of all internal combustion engines. Modern engines operate at higher temperatures and therefore run more efficiently - less of the energy produced by burning fuel is turned into heat, and more of the energy is used to power the vehicle. However, they still produce excess heat.

The engine is equipped with a cooling system designed to remove much of the excess heat. When functioning properly, the cooling system maintains an optimum temperature for the engine.

RADIATOR

The radiator is used to dissipate the excess heat from the hot coolant. At operating temperature, some of the engine coolant circulates through the radiator and gives up its heat to the outside air, as it passes across the radiator. So the radiator is a "heat exchanger."

Scheme 50

COOLANT RECOVERY TANK

The engine cooling system is equipped with a reservoir to maintain a constant supply of coolant in the system. When the coolant is hot, it expands into the reservoir; when it cools, it contracts and flows from the reservoir into the radiator. The surge tank is transparent, so that the fluid level can be checked periodically, to ensure that the coolant level is adequate.

The level of coolant in the reservoir should be above the bottom line ("Kalt") when the engine is cool and below the top line ("Heisse") when the engine is at operating temperature.

Scheme 51

COOLANT LEVEL CHECK

To check coolant level, allow engine to cool down; coolant temperature may not exceed 30°C. If ambient temperature is above 30°C, then allow engine to cool down at least to ambient temperature.

Check coolant level, top up coolant if necessary until float is in line with top edge of expansion tank.

Note. Tank mark indicates the fluid level at approx. 20°C. Use only recommended coolant.

Scheme 52

RADIATOR CAP

The reservoir has a pressure cap, which is designed to maintain pressure in the cooling system. As the engine warms up, coolant temperature increases and the coolant expands. The pressure cap prevents the expanding coolant from escaping and results in a pressure increase in the system. This raises the coolant's boiling point. This allows the cooling system to maintain the correct engine operating temperature without boiling over.

Scheme 53

The radiator cap has both pressure and vacuum valves. At the rated pressure, the pressure valve opens, to allow vapor to escape into the atmosphere and coolant to flow into the reservoir due to expansion. This prevents excess pressure from building up in the system.

When the engine is stopped and allowed to cool off, the pressure in the cooling system drops from a pressure that is higher than the atmospheric pressure, to one that is lower. At this point, the vacuum valve opens to allow ambient air to enter the reservoir, and pressure in the system equals atmospheric pressure. If the coolant level in the radiator is low during this period, coolant will be drawn into the radiator.

Scheme 54

MAIN COOLING FAN

The radiator is equipped with a main cooling fan that is either electrically powered or engine driven via a belt, the water pump pulley, and a viscous clutch.

The viscous clutch reduces fan speed when cooling requirements are low. The clutch contains a small fluid coupling partially filled with a special silicone oil. When engine cooling requirements are high (during high-temperature operation), more oil is injected into the fluid coupling. This causes more power to pass through the coupling, so that fan speed increases. When cooling requirements are low (for example, during cool-weather operation), oil is withdrawn from the fluid coupling. Less power passes through and fan speed drops off.

Even when engine cooling requirements are high, there is still a small amount of slip (The coupling does not lock up). This allows the oil to continue to circulate through the fluid reservoir and the coupling.

The amount of oil in the fluid coupling, and the resulting fan speed, are controlled by a thermostatic strip. The strip bows outward with increasing under-the-hood temperature. This motion allows a control piston to move outward. As the piston moves outward, more oil is forced into the coupling, causing the fan speed to increase.

Scheme 55

ENGINE COOLANT

The cooling system contains a special liquid called coolant, or "antifreeze," which circulates through the engine and the radiator. The coolant picks up heat from the engine and transports it to the radiator, where it is dissipated to outside air. Some of the hot coolant can also be circulated through the heater core, where it can warm the air being blown into the passenger compartment.

The antifreeze concentration should be 50%, throughout the year. In addition, the coolant should be drained and refilled according to the recommendations in the BMW Operating Fluids Specifications, Group 17.

The cooling system does not need any additives besides a reputable brand of ethylene glycol antifreeze with corrosion inhibitors that are nitrite- and amino-acid free and compatible with aluminum radiators. Antifreeze other than the type specified by BMW for aluminum radiators may cause corrosion of the cooling system, which can lead to engine overheating and damage.

Water Pump

A water pump, driven by a belt from the crankshaft, is used to pump coolant through the cooling system.

Many BMW models have an auxiliary electric water pump to ensure adequate coolant flow to the heater core, especially at low engine RPM and very cold ambient temperatures. (Also models equipped with rest feature)

Engine Thermostat

There are two types of thermostats in BMW cars, the mechanical type, and the type that is electrically heated. Both are designed to bring the temperature of the coolant up to operating temperature quickly.

When the engine is cold, the thermostat is closed; in the closed position, it sends coolant from the engine back to the engine, through a bypass; as a result, the coolant temperature rises quickly. As the coolant reaches the rated temperature, the thermostat gradually opens, to allow coolant to flow from the engine to the radiator.

Scheme 56

Electronically Heated Thermostat

The heated thermostat is both a conventionally functioning and ECM controlled thermostat (two stage operation).

ECM control causes the thermostat to open sooner than the mechanical thermostat rating. This provides sufficient cooling for full load and high output conditions.

Scheme 57

CONVENTIONAL FUNCTION: The thermostat begins to open at 103°C. This is at the inlet side of the water pump and represents the temperature of the coolant entering the engine.

Before the 103°C temperature is realized, the coolant is circulated through the engine block by the water pump.

Scheme 58

After the temperature reaches 103°C it is maintained as the inlet temperature by the thermostat. The coolant temperature at the water pump engine outlet is approximately 110°C. The additional 7°C is achieved after the coolant has circulated through the block.

The operating temperature of the engine will remain within this range as long as the engine is at part load conditions.

Scheme 59

ECM CONTROLLED FUNCTION

The map controlled heater in the thermostat will switch ON under the following conditions

1. Load signal "ti" > 5.8 ms
2. Engine temperature "tm" > 113°C
3. Intake air temp > 52°C
4. Vehicle speed > 110 MPH

When the heating element is switched ON, the thermostat is heated higher than the temperature of the coolant.

The thermostat opens sooner causing additional coolant to circulate through the radiator which brings the temperature down.

The temperature of the coolant at the inlet side of the water pump will drop to approximately 85°C and the temperature at the outlet side of the water pump will drop to approximately 103°C.

Scheme 60

Note. If the coolant temperature is below 85°C, the heater will not switch on for any condition. The display characteristics of the temperature gauge in the instrument cluster have been calibrated to the higher engine temperatures.

WATER VALVE(S)

The heating system utilizes hot coolant from the engine cooling system to warm air for heating the passenger compartment. The amount of coolant that flows into the heating system is controlled by an electric water valve(s).

The water valve is electrically actuated. It is located beside the brake booster. It controls coolant flow through the heater core. The valve is powered closed by an electric switch; when not powered, it springs open. The valve, when powered closed, prevents hot coolant from entering the heater core, so the air entering the passenger compartment is not heated. When power is removed, the valve springs open, so that hot coolant flows through the heater core and can warm the air entering the passenger compartment.

The E31, E32, E34, E36 (IHKR and IHKA), E38, and E39 cars use pulsed water valves to control the heater core temperature.

Scheme 61

Scheme 62

HEATER CORE

When the water valve is open, hot engine coolant circulates through the heater core. The heater core heats the air that passes through it; the hot air can then be used to warm the passenger compartment. The heater core (like the radiator) is also a "heat exchanger."

Scheme 63

This can cause overheating with permanent damage to the engine

Recycling!

Catch and dispose of drained coolant. Observe country-specific waste-disposal regulations.

HEATING AND AIR CONDITIONING SYSTEM COMPARISONS

AIR CONDITIONING SPECIFICATION CHART

Many parallels can be drawn between the cooling system and the air-conditioning system. With a thorough understanding of the cooling system, air-conditioning becomes easier to comprehend.

The basic difference is that refrigerant has a much lower boiling point and goes through changes of state which produce much higher system pressures. This is why the components and servicing equipment are made to contain high pressures.

Basic Principle Of Air Conditioning

The basic principle at work in a climate control system is heat transfer. An automotive A/C system takes heat inside the passenger compartment and transfers it outside.

Scheme 64

In an A/C system, heat is transferred using a refrigerant. The refrigerant absorbs heat from air entering the passenger compartment, carries the heat outside the compartment, releases the heat, and then re-enters the compartment to begin the cycle again.

An A/C system does not "add cold" to air - it removes some of the heat from it. Some heat is always present, but the less heat the air contains, the cooler it feels.

Temperature

The amount of heat energy present is measured as the temperature. There are two different temperature scales, Fahrenheit and Celsius.

Scheme 65

BTUs And Calories

Heat is measured in British Thermal Units (BTUs) and calories.

Scheme 66

1. BTU - amount of heat energy required to raise one pound of water one degree Fahrenheit.
2. Calorie - amount of heat energy required to raise one gram of water one degree Celsius.

Heat Transfer

An air conditioning system's efficiency is based on how well it moves heat. Heat always travels from warm to cold. The reverse is never true. For example, if a hot cup of coffee is left standing, it will cool off, while a cold soda will get warm. The heat from the warm coffee moves to the cooler surrounding air. The heat from the surrounding air moves to the cooler soda, until a balance is reached.

Scheme 67

Temperature And State Changes

At sea level, water freezes at 32 F (0°C) and boils at 212°F (100°C). These are the temperatures at which water changes state.

When a liquid boils (changes to a gas), it absorbs heat. When a gas condenses (changes back to a liquid), it gives off heat.

Water requires one BTU of heat per pound to rise one degree Fahrenheit. If you place one pound of water at 32°F in a container over a flame, its temperature rises 1°F for each BTU of heat the water absorbs from the flame. Once the water has reached a temperature of 212°F, it has absorbed 180 BTUs of heat.

Scheme 68

As the flame continues to heat the water, it boils, changing from a liquid to a gas, and it continues to boil until all of it has changed to a gas.

If this gas is collected in a container and checked with a thermometer, it would also have a temperature of 212°F. The temperature has not risen further, but the flame has applied an additional 970 BTUs of heat. The heat is absorbed by the liquid as it boils. It is "hidden" in the water vapor.

Scheme 69

If the vapor contacted cool air, the heat would flow into the cooler air as the vapor condensed back into water. This hidden heat is called the "latent (hidden) heat of vaporization."

Water has a latent heat of vaporization of 970 BTUs. This means one pound of water at 212°F will absorb 970 BTUs of heat when it boils and becomes a vapor. In the same way, the vapor will give off 970 BTUs of heat when it condenses back to water.

Scheme 70

Scheme 71

In other words, water acts like a "heat sponge": it soaks up a small amount of heat (180 BTUs per pound) when its temperature rises from 32°F to 212°F; and it soaks up a large amount of heat (970 BTUs per pound) when it changes from a liquid to a gas.

Evaporation

Evaporation is one of the basic principles by which a refrigeration system works. In evaporation, liquid changes to a vapor. Adding heat causes a liquid to evaporate.

Scheme 72

Condensation

Condensation is the reverse of evaporation. In condensation, a vapor changes to a liquid. Removing heat causes a vapor to condense to a liquid.

Scheme 73

The task of an air conditioning system is to absorb a large amount of heat, move it away from the passenger compartment, and exhaust it. When the refrigerant in the A/C system evaporates, it absorbs a large amount of heat from the air entering the passenger compartment. As the refrigerant vapor is pumped outside the passenger compartment, it transports this heat with it. When the refrigerant condenses back into a liquid, this heat is released.

Scheme 74

1. As the pressure on a liquid is increased, the boiling point rises.
2. As the pressure on a liquid is decreased, the boiling point drops.

At sea level, where the atmospheric pressure is 14.7 psi, the boiling point of water is 212°F (100°C). At any point higher than sea level, the atmospheric pressure is lower and so is the boiling point. In Denver, Colorado (elevation 5,300 feet), water boils at only 206°F (97°C).

Atmospheric pressure is approximately 14.7 psi (absolute) at sea level, and somewhat lower at higher elevations. At sea level, the entire weight of a "column" of air approximately 600 miles high, presses down on everything. At higher elevations, the column of air is shorter and the air is thinner, so the pressure is lower.

Scheme 75

Of course, you don't notice the 14.7 psi pressing in on everything, and air pressure gages are calibrated to read 0 psi at atmospheric pressure. But this atmospheric pressure exists, and you can feel its effects, particularly at higher elevations; for example, if you exercise vigorously, at a high elevation, you become winded more quickly.

Scheme 76

In an air conditioning system, the pressure in the evaporator is low, so that all the refrigerant vaporizes. The pressure in the condenser is high, so that all the refrigerant readily changes state to a liquid.

Scheme 77

Raising the pressure of a vapor raises its temperature; lowering the pressure decreases its temperature.

Scheme 78

In an air conditioning system, a compressor is used to increase the pressure of the refrigerant; this raises its temperature. The refrigerant vapor entering the condenser is hot.

In BMW air conditioning systems, an expansion valve is used to lower the pressure of the refrigerant; the refrigerant in the evaporator is cold.

Automotive A/C systems are designed to operate at pressures that keep the refrigerant at the optimum temperature for taking heat out of the passenger compartment.

The "Comfort Zone"

1. Temperature / 70° to 80°F (21° to 27°C).
2. Humidity / 45% to 50% (at 70° to 80°F).
3. Movement of air around the body (the more air, the cooler the body feels).

Air Conditioning And Comfort

The purpose of an A/C system is to make the driver and passengers comfortable. An A/C system achieves this by cooling the air temperature inside the passenger compartment and removing moisture (humidity), dust, and pollen particles.

Scheme 79

By removing moisture and lowering the humidity, an A/C system can achieve passenger comfort at higher temperatures. The reason for this is that the human body cools itself by allowing moisture on the skin to evaporate.

The relative humidity governs how quickly evaporation occurs

1. High relative humidity = low evaporation rate.
2. Low relative humidity = high evaporation rate. When the A/C system removes moisture from the air, the relative humidity in the passenger compartment decreases. By reducing the relative humidity, the A/C system increases the rate at which the moisture on passengers' skin will evaporate.

AIR CONDITIONING (A/C) SYSTEM

The air conditioning system is a self-contained system, completely sealed off from the atmosphere. While operating, it recycles refrigerant through the system.

The major components of the A/C system include

1. The compressor
2. The condenser
3. The receiver/dryer
4. The expansion valve
5. The evaporator

When the A/C compressor clutch is engaged, the compressor draws in low-pressure refrigerant gas. It compresses the gas and moves it to the condenser. Compressing the gas raises its temperature above that of the outside air. As the hot, high-pressure gas flows into the condenser, cooler air flowing across the condenser absorbs heat from the gas. As the refrigerant gives up heat to the air, it condenses and changes to a liquid.

The high-pressure liquid refrigerant flows from the condenser to the receiver/dryer. The dryer contains a filter screen, to remove small impurities, and a drying agent to absorb and hold any moisture. The dryer is also a storage tank; a steady supply of liquid refrigerant is drawn out of the bottom of it, to the expansion valve. The expansion valve meters the refrigerant, so that its pressure drops, causing it to boil as it enters the evaporator.

Hot air is blown across the evaporator as the refrigerant boils. Heat from the air is transferred to the refrigerant, causing the air to be cooled. The hot, low-pressure refrigerant is then drawn back into the compressor to complete the loop.

In addition to cooling the air, the A/C system also dehumidifies it.

Additional components of the A/C system include

1. The compressor clutch
2. The pressure switches
3. The evaporator temperature sensor The compressor clutch allows the compressor to be disengaged when the A/C system is not used. The pressure switches cause the compressor clutch to disengage when the pressure in the system is too low or high, to prevent damage. The evaporator temperature sensor also causes the compressor clutch to disengage when the evaporator temperature drops close to freezing. This prevents ice or frost from forming on the evaporator fins.

Scheme 80

REFRIGERANT

An air conditioning system uses refrigerant to absorb heat from the air that passes through the evaporator. Refrigerants are special materials that are vapors at room temperature and liquids at much lower temperatures. Automotive refrigerants, for example, boil at -16°F to -22°F (-27°C to -30°C). Refrigerants are also able to contain and transport a large amount of heat, efficiently; and they can be evaporated and condensed over and over without being damaged.

In the air conditioning system, liquid refrigerant under high pressure flows through a small hole into the evaporator, where the pressure is then greatly reduced. When the pressure drops, the refrigerant boils and changes from a liquid to a vapor. As it changes its state, it absorbs a large amount of heat.

As the air passing through the evaporator gives up some of its heat, it becomes colder; it can then be blown into the passenger compartment, to cool it.

Once the refrigerant has absorbed heat from the air, it is returned to the compressor. The A/C system removes the excess heat from the refrigerant as the refrigerant passes through the condenser.

There are two types of refrigerant used in BMW vehicles; these will be discussed later in

Scheme 81

1. The oil should be replaced whenever a ruptured component is replaced, because the quick discharge causes some of the oil to be released along with the refrigerant
2. Use only PAG oil in an R-134a system (not mineral oil)
3. Use only mineral oil in an R-12 system (not PAG oil).
4. Add the right amount of oil into the system when replacing a major component such as the compressor, condenser, or evaporator. When replacing the compressor, drain the oil from the old compressor and measure the amount. Turning the clutch plate by hand helps "pump" out any remaining oil. Inject an equal amount of fresh oil. Note: service compressors are shipped full of oil; this oil must be drained before the new compressor is installed. When replacing the condenser or evaporator, add 2 oz. of oil to the system. When replacing a receiver/dryer, add 1 oz. of oil to the system. You do not need to add any oil when replacing a hose, since hoses do not collect much oil.
5. Oil can be added to a charged system using the Robinair 18065 oil injector and a manifold gauge set, or the injector bottle on the ACR4 unit.

COMPRESSOR

The compressor in an automotive A/C system serves two important functions

1. It creates a low-pressure zone at the compressor inlet, to draw refrigerant vapor from the evaporator.
2. It compresses the low-pressure refrigerant vapor into a high-pressure vapor and sends it toward the condenser.

BMW A/C systems use various types of compressors. These include

Scheme 82

1. Seiko-Seiki rotary vane compressor
2. Nippondenso swash-plate design

The Seiko-Seiki type is a five-vane rotary compressor. It consists of a shaft with vanes, that maintain contact with the inner wall of a cavity. The cavity is shaped like an ellipse. As the shaft rotates, oil pressure and centrifugal force push out on the vanes, so that their outer edges stay in contact with the cavity. This creates spaces where the volume is expanded and contracted, to draw refrigerant vapor in, compress it, and force it out.

Scheme 83

When the space between the shaft and the cavity is large, the pressure is low. Refrigerant vapor is drawn into the space. When the vane passes the inlet port, the space is sealed off; no more refrigerant vapor can be drawn in. As the vane sweeps through 180°, the space shrinks, compressing the refrigerant. The refrigerant is then forced out through reed valves, to the discharge ports.

Scheme 84

The Nippondenso compressor is a five cylinder swash-plate compressor. The swash plate is set on an angle, and it rotates with the shaft. As it goes through one complete revolution, it drives pistons from one end of their travel to the other, and back again. As it drives a piston forward in its cylinder, the piston compresses the refrigerant in the cylinder. The compressed refrigerant is then discharged. As the swash plate pulls a piston back, the piston draws refrigerant into the cylinder.

Scheme 85

Scheme 86

COMPRESSOR REGULATION - COOLING

The E39, 9/97 E38 750iL, E46 - IHKA uses a new variable displacement A/C compressor.

The swash plate of the compressor is hinged so that it can vary the piston travel based on the output requirements of the system. The swash plate position is controlled by the control valve located in the compressor.

The control valve regulation is based on the low and high side pressures of the system. A "high" low side pressure (high load) will cause the control valve to close and block discharge pressure from entering into the crankcase of the compressor.

Scheme 87

When the low side pressure decreases, the control valve opens. The swash plate moves to a position of minimum travel and consequently reduces the compressor output.

The compressor output varies continually based on the constant change in the contributing pressures.

Scheme 88

At low engine RPMs and/or high temperature loads, the piston travel (displacement) of the compressor pistons are at the maximum point. This allows the compressor to provide maximum cooling efficiency at idle speeds and when high output is required (heavy demand for cooling).

Scheme 89

At higher engine RPMs and when the load on the system is low, the swash plate moves so that the piston travel is shortened.

This reduces the constant high load output of the compressor any time the A/C system is on. It also reduces the cycling of the compressor due to the low temperature of the evaporator (evaporator temperature sensor causing the system to cycle at 3°C). An overall effect of this is improved fuel economy.

Scheme 90

COMPRESSOR CLUTCH

The compressor pulley is driven by a belt from the crankshaft; a compressor clutch is used to engage/disengage the pulley and driveshaft. The clutch is electromagnetic. When power is provided to the clutch, the clutch engages and rotates the compressor drive shaft. When the power is cut off, the clutch disengages and the compressor pulley freewheels. On BMW A/C systems, the compressor is cycled on and off, according to evaporator temperature; it is also cycled off at full-throttle, standing start acceleration conditions.

Scheme 91

A diode is used to prevent induced current and voltage from damaging the control module/relays when the clutch solenoid is disengaged. The diode allows the voltage spike created when the clutch solenoid is disengaged, to flow in a loop back through the solenoid coil, until the energy is dissipated. Different vehicles use different control modules to control the compressor clutch.

Scheme 92

The compressor clutch is unit replaceable.

COMPRESSOR SERVICE

1. When troubleshooting a noisy compressor complaint, make sure the noise is present only when the clutch is engaged.
2. If it is present when the clutch is not engaged, remove the compressor drive belt and check again.
3. If the noise continues, it is not related to the compressor.
4. If removing the drive belt reduces or eliminates the noise, check the torque of the compressor and bracket mounting bolts.
5. Check the belt tension and condition, and tensioner pulleys which can produce rattling noises that would sound like a defective compressor.
6. A loose/slipping belt can cause noise.
7. A belt that is too tight can damage the clutch bearings.
8. If the compressor is noisy with the compressor clutch engaged, make sure the system is charged with the correct amount of refrigerant.
9. An over-charged system can cause compressor noise.
10. If the A/C system is overcharged with refrigerant, the liquid entering the compressor can damage it.
11. When troubleshooting a noisy compressor complaint, recover the refrigerant and recharge the system with the correct amount.
12. A failed compressor must be returned with the inlet and outlet ports sealed using the plastic caps from the replacement compressor. Otherwise the "failed" compressor will be damaged by moisture, and it will be impossible for Warranty to analyze it.

CONDENSER

The compressor pumps the refrigerant to the top of the condenser. Almost all of it is a high-pressure vapor, at this point. Because of its high pressure, the temperature at which it can condense is much higher. The high pressure allows the refrigerant to change from a vapor to a liquid, when ambient air, passing over the condenser, carries some of its heat away. Most of the refrigerant is a high-pressure liquid by the time it reaches the bottom of the condenser. The condenser (like the radiator and the heater core) is also a "heat exchanger."

Scheme 93

The condenser on BMW A/C systems is equipped with an auxiliary fan that provides additional air flow through the radiator and condenser, when needed.

Auxiliary fan control systems vary from vehicle to vehicle. The following is a typical "basic" example of how an auxiliary fan is controlled.

The auxiliary fan is controlled by two normally open relays, a normal-speed relay, which runs the fan at the "normal" speed; and a high-speed relay, which runs the fan at the "high" speed.

The A/C control module grounds the normal-speed relay whenever the A/C system is turned on. This causes the fan to run at the normal speed.

The relays are also energized by a (normally open) double temperature switch, which senses coolant temperature in the radiator. When coolant temperature rises above 180°F (82°C), the normal-speed half of the switch closes, powering the normal-speed relay, and the auxiliary fan runs at the normal speed, whether or not the snowflake button is depressed.

When the temperature rises above 190°F (88°C), the high-speed half of the switch closes, powering the high-speed relay, and the auxiliary fan runs at high speed.

There is also an intermediate pressure switch fitted to the receiver/dryer. This switch, which is normally open, closes when refrigerant pressure exceeds 260 psi. This energizes the high-speed relay and runs the auxiliary fan at high speed.

Scheme 94

AUXILIARY FAN CONTROL - E46 & E38, E39 (as equipped)

The Auxiliary Fan motor incorporates an output final stage that activates the fan motor at variable speeds.

The auxiliary fan is controlled by ECM. The motor output stage receives power and ground and activates the motor based on a PWM signal (10 - 100Hz) received from the ME 7.2.

The fan is activated based on the following factors

Scheme 95

1. Radiator outlet temperature sensor input exceeds a preset temperature.
2. IHKA signalling via the K and CAN bus based on calculated refrigerant pressures.
3. Vehicle speed.
4. Battery voltage level

When the over-temperature light in the instrument cluster is on (120°C) the fan is run in the overrun function. This signal is provided to the DME via the CAN bus. When this occurs the fan is run at a frequency of 10Hz.

Scheme 96

Scheme 97

From the condenser, liquid refrigerant under high pressure flows to the receiver/dryer. The receiver/dryer consists of a cylindrical tank to hold the refrigerant and a solid dryer (comprised of a desiccant such as silica gel, for an R-12 system, or zeolite, for an R-134a system; molecular sieves; and aluminum oxides). The receiver/dryer is designed to separate refrigerant vapor from liquid, so that only liquid is fed to the expansion valve.

The liquid refrigerant enters the tank on the side and flows downward through the solid dryer. Contamination is filtered out by the screen. The dryer absorbs moisture, dirt and acid. However, the dryer element can only absorb a small amount of moisture (6-10 grams for an R-12 system; and 10-16 grams for an R-134a system). Early receiver/dryers have two pressure switches, a high-pressure cutoff switch and a low-pressure cutoff switch. Later receiver/dryers have a combination high/low cutoff switch. These switches interrupt power to the compressor clutch when pressure in the refrigerant circuit is too low or too high.

R-134a receiver/dryers are now used to replace R-12 receiver/dryers.

Repair Procedure

Replace the high pressure switch along with the receiver/dryer if the fusible plug is found open.

The following items should also be checked for proper function as the system should not normally operate at these high pressures

1. Auxiliary Fan
2. 108°C Coolant Temperature Switch (M Series Cars Only)
3. 150°C Compressor Temperature Switch (models so equipped)
4. Operating pressures - blockage or restriction in system

PROPER READING OF THE SIGHT GLASS

On R-12 A/C systems, look at the sight glass of the receiver/dryer. This will provide preliminary information on the condition of the refrigerant. With an R-12 system, there will be differences between the cold and hot weather appearance of the sight glass. Generally speaking, bubbles tend to appear in hot weather and are slow to appear in cold weather.

Scheme 98

Scheme 99

Scheme 100

1. A few bubbles show up 2 - 3 seconds after the compressor cycles on.
2. High-pressure side is hot and low-pressure side is cold.
3. Refrigerant is sufficient.
4. Bubbles flow continuously; oil streaks.
5. Almost no difference in temperature between low- and high-pressure sides.
6. Likely to be very little refrigerant.
7. "Mist"-like flow, with bubbles totally absent.
8. No difference in temperature between the low- and high-pressure sides.
9. Probably means no refrigerant.
10. A few bubbles show up intermittently, at intervals of 1 - 2 seconds.
11. High-pressure side is warm and low-pressure side is fairly cold.
12. Refrigerant likely to be insufficient.

R-134a RECEIVER/DRYER

The basic design of R-12 and R-134a receiver/dryers is the same. However, while R-12 systems typically use silica gel as a desiccant, R-134a systems use Zeolite. The drying capacity (per weight) of zeolite is only about 25% that of silica gel so R-134a receiver/dryers are larger, to accommodate larger amounts of desiccant. In addition, the high-pressure cutoff switch is rated higher for an R-134a receiver/dryer, since the system operates at higher pressures.

Scheme 101

NOTES ON REPLACING DRYER FLASK

The dryer flask must be replaced when

1. there are contaminants in the refrigerant circuit (e.g. compressor has seized)
2. the system is leaking and there is no more refrigerant in the system
3. the refrigerant circuit was opened for longer than 24 hours during a repair.

Scheme 102

The expansion valve controls the amount of refrigerant released into the evaporator. It is fitted to the evaporator inlet/outlet pipes. The valve separates the high-pressure side of the system from the low-pressure side. A small passage, or "orifice," allows only a small amount of liquid into the evaporator. The amount of refrigerant that it allows through depends on the evaporator temperature and pressure, and the temperature of the air passing through the evaporator.

If too little refrigerant enters the evaporator, poor cooling results. If too much refrigerant enters, it might not completely boil away and liquid refrigerant might return to the compressor, causing damage to the system.

A block-valve design of expansion valve is used on current BMW A/C systems. The refrigerant enters at the upper right inlet. At the left of the valve there is a capillary tube filled with an inert gas, that senses the temperature of the air coming into the housing from the plenum. When the air temperature in the plenum rises, the pressure in the capillary tube increases. This pushes down on a diaphragm and pushrod assembly, which increases the size of the orifice opening, allowing more refrigerant into the evaporator and providing more cooling. When plenum temperature falls, the pressure in the capillary tube falls. The spring pushes up on the pushrod, making the orifice opening smaller; less refrigerant is allowed into the evaporator, allowing less cooling.

Scheme 103

Refrigerant from the outlet of the evaporator passes through the bottom left opening of the block valve. When the pressure at the evaporator outlet is high, this increases the pressure needed by the capillary tube, to open the valve. Less refrigerant is provided to the evaporator (to prevent the evaporator from being flooded). When pressure at the outlet end of the evaporator is lower, less pressure is exerted on the bottom of the diaphragm.

The diaphragm pushes down on the pushrod, allowing more refrigerant into the evaporator.

Note. The R-134a system expansion valve uses a different operating pressure range. This enables the valve to work more efficiently with the new refrigerant. An expansion valve designed for use in an R-12 system, if installed in an R-134a system may not allow enough refrigerant into the evaporator. This may affect the performance.

If moisture gets into this system, it may freeze and clog the expansion valve. The A/C system may operate normally for a while, but then stop cooling. Then, as system temperature increases, the ice melts. The system works again for a while, until moisture freeze-up causes it to stop again. For diagnosis and correction of this problem, see R-134A RECEIVER/DRYER .

The expansion valve is unit replaceable; there are no adjustments or repairs.

Scheme 104

From the expansion valve, the liquid refrigerant passes into the evaporator. Once the refrigerant passes the orifice in the expansion valve, its pressure drops. The liquid refrigerant, now in the evaporator, immediately begins to boil. As it boils, it absorbs heat from the air that passes over the fins and tubes of the evaporator. This cools the air and heats the refrigerant. The refrigerant, now a vapor again, is then drawn back into the low side of the system by the compressor.

The evaporator on current BMW cars is mounted crosswise in the housing. It is similar in construction to a radiator (a copper or aluminum coil with fins). The fins provide a large surface area to transfer heat from the air to the colder refrigerant inside the coil. The evaporator (like the condenser) is a "heat exchanger."

Scheme 105

As air passes over the evaporator fins, the moisture condenses on the fins as the air cools. Water collects in the bottom part of the housing and exits through one or two drains.

Evaporator service

1. Check water drains.
2. Straighten bent fins (a tool is available locally)
3. A frost ring on a tube indicates a restriction. (On some vehicles, the evaporator and expansion valve can be accessed by removing the glove box.)

Scheme 106

If the evaporator temperature is allowed to cool below 1°C, condensation can freeze on the evaporator. The ice then insulates it from the air passing over it, and it works much less efficiently. A temperature sensor is used to protect the evaporator from freezing, by signaling the control module to turn the compressor off, so that condensation cannot freeze on the evaporator. The compressor is typically disengaged at 34°-37°F (1°-2°C). When the compressor is turned off, refrigerant flow is reduced and the evaporator temperature rises.

The temperature sensor is a Negative Temperature Coefficient (NTC) thermistor whose resistance varies according to the temperature of the evaporator core. Resistance is higher at lower temperatures, and decreases as the temperature rises.

Scheme 107

A dual squirrel-cage blower is used (on most BMWs) to propel air across the evaporator and/or the heater core and through the plenum to the vents. On BMW A/C systems, the blower speed is controlled by resistors/transistors that vary the amount of voltage applied to the blower, depending on the air volume control knob setting. In IHKA systems, the blower speed is controlled electronically.

Whenever the A/C is switched on, the fan runs at speed "1" or higher. Without the fan working, the evaporator could ice up, as humid air comes in contact with the fins.

Scheme 108

MICROFILTERS

Microfilters are used in BMW climate control systems, this includes all vehicles produced after 9/91 (except E30). In addition, all E31 vehicles have been equipped with microfilters since start of production.

Scheme 109

Shown in the above example is an E38 microfilter and location. Fresh air is continuously filtered through the microfilters. Never operate an E38 without the microfilters installed, there is the danger of water being drawn into the heater and/or damage to the electrical system.

The microfilter is designed to trap potentially irritating types of particles with very high efficiency. Some examples include

1. Pollens
2. Spores
3. Dust
4. Vapors
5. Floating air pollution
6. Bacteria
7. Viruses

Under normal operating conditions the microfilter(s) should be replaced every Inspection I and II (also every Oil Service 99 MY), except for M roadster or M coupe. The actual service life of the microfilter depends on the amount of contaminant and air flow rate reduction complaint, therefore; the replacement interval may be more frequent in dusty operating conditions.

E38 models have additional filters for the recirculation air inlets which require replacement at every second inspection II.

Scheme 110

R-12

R-12 or Freon(R), was used in BMW air conditioning systems prior to 1992. It is a member of the class of compounds called "chlorofluorocarbons" (CFC's).

Characteristics

1. Very durable.
2. Transports heat very efficiently.
3. Non-explosive when mixed with air.
4. Odorless; not harmful to human health when handled correctly.
5. Boils at -22°F (-30°C).
6. Absorbs a large amount of heat when boiling.
7. Does not react with most metals (except lead).
8. Reacts with many synthetics.
9. Reacts with water to produce acid.
10. Mixes readily with mineral-based oil.

Skin should not be exposed to liquid R-12. Since R-12 boils at -22°F (-30°C), it can cause severe frostbite or freezing damage.

R-12 should never be exposed to an open flame. When it burns in air, it produces phosgene, a poisonous gas.

R-12 should be stored at room temperature, and not exposed to extreme heat.

A serious environmental problem has been created by discharging R-12 refrigerant into the atmosphere. CFC's cause very long-term damage to the stratospheric ozone layer.

Scheme 111

One molecule of R-12 can destroy many molecules of ozone. In the upper atmosphere, ultraviolet light breaks off a chlorine atom from an R-12 molecule.

The chlorine attacks an ozone molecule, breaking it apart. An ordinary oxygen molecule and a molecule of chlorine monoxide are formed.

A free oxygen atom breaks up the chlorine monoxide. The chlorine is then free to repeat the process.

Scheme 112

The ozone in the stratosphere blocks most of the ultraviolet-B radiation from the sun, thus preventing it from damaging plants and animals. Without the protection of stratospheric ozone, plants and animals are exposed to damaging levels of UV-B.

R-134a

For this reason, a new refrigerant, R-134a, has been developed. It does not contain chlorine (it's a "hydrofluoro-carbon," or "HFC"). It causes much less damage to stratospheric ozone.

Scheme 113

Despite the much lower risk of environmental damage, it's still important to handle R-134a responsibly. BMW technicians should do their part to maintain a safe environment for future generations.

Characteristics of R-134a

1. Very durable.
2. Transports heat very efficiently
3. Density, pressure, boiling point similar to R-12.
4. Extremely hygroscopic (absorbs water very readily).
5. Non-toxic, non-flammable; slight ether-like smell.
6. Contains no chlorine atoms; will not damage stratospheric ozone.
7. R-134a pressures tend to rise sooner and higher as temperature increases.

PHYSICAL CHARACTERISTICS SPECIFICATION CHART

IDENTIFICATION OF R-12 AND R-134a CONTAINERS

CONTAINERS SPECIFICATION CHART

Although R-12 and R-134a are similar in some ways, the refrigerants must never be mixed or combined in any way.

BASIC SYSTEM DIFFERENCES: R-12 vs R-134a

Scheme 114

1. R-134a pressures are higher than R-12, as temperature increases.
2. Compressor oils: R-12 systems use mineral oil. 134a systems use PAG oil.
3. Underhood labels: R-12: black. R-134a: green.

Note. Charging amount should be according to the underhood label.

Scheme 115

DESCRIPTION CHART

REFRIGERANT HANDLING CERTIFICATION REQUIREMENTS EQUIPMENT REQUIREMENT

Since Jan. 1, 1993, any technician servicing, repairing, or opening a motor vehicle air conditioning system "for consideration" - anything other than free service- must use either refrigerant recovery/recycling or recovery-only equipment approved by the EPA.

There are certification requirement for the technicians and the equipment; there are also record-keeping requirements.

Technician Training/Certification

Technicians using approved equipment must be trained and certified by an EPA-approved organization, such as your BMW training center. To be certified, technicians must pass a test demonstrating their knowledge in the use of recycling equipment in compliance with SAE Standard J1989, the regulatory requirements, the importance of refrigerant containment, and the effects of ozone depletion.

Equipment Certification

The equipment owner or another responsible officer must certify (report) to the EPA that they own approved equipment. The information provided must include the name, address, and telephone number of the establishment where the recovery/recycling equipment is located; the name brand, model number, year and serial number(s) of the equipment acquired for use at the establishment; and the signature of the person who acquired the equipment (the owner or another responsible officer), certifying that they have acquired the equipment, that each individual authorized to use the equipment is properly trained, and that the information provided is true and correct.

RECORD-KEEPING REQUIREMENTS

If the refrigerant is recovered and sent to a reclamation facility, the name and address of that facility must be retained.

Important Dates

Jan. 1, 1992: Since this date, containment and recycling of R-12 have been required.

Nov. 14,1994: Since this date, the sale of refrigerant in any size container is restricted to certified technicians.

July, 1995: Since this date, any R-12 mobile air conditioning system that is converted to use an acceptable alternate refrigerant must have the appropriate unique service fittings and label for that refrigerant.

Nov. 15, 1995: Since this date, recovery and recycling of any substitute substance for R-12, such as R-134a, used in a motor vehicle air conditioner have been required.

Scheme 116

Recommended Refrigerant Recovery, Recycling, Evacuation, And Charging Equipment

A proper system charging station includes the following components

1. A manifold gauge set.
2. A charging cylinder.
3. A bulk refrigerant supply tank.
4. A vacuum pump.
5. Hoses for connection to the automotive A/C system.
6. An electronic leak detector.
7. A thermometer.

This setup will allow you to evacuate and charge an A/C system.

For handling R-12 refrigerant, use an R-12 recycling unit (such as the Kent-Moore ACR3).

Scheme 117

For R-134a refrigerant, a different unit is used (the Kent-Moore ACR4). These units filter and remove moisture the refrigerant, before discharging it into a recovery tank.

Scheme 118

Never use any R-12 service tool, such as manifold gauge sets, on R-134a systems. Tools retain small amounts of refrigerant and lubricant. Attempting to use the same equipment on both R-12 and R-134a vehicles will contaminate the air conditioning systems. Manifold gauge sets must be constructed of the proper hose material and fitting to be compatible with R-134a. Compatible units should be labeled be appropriately.

When servicing is completed, the protective sealing caps must always be reinstalled to prevent contamination via the service fittings.

The R134a system (early models) uses a standard sight glass to view the refrigerant charge. The sight glass view may turn "cloudy" if the wrong compressor oil is used.

Scheme 119

Scheme 120

R-12 and R-134a systems use different leak detectors. An R-12 leak detector will not detect R-134a leaks (R-134a molecules are much smaller than R-12 molecules). However, an R-134a leak detector will detect R-12 leaks (be sure to follow the manufacturer's instructions carefully to avoid contamination).

An R-12 leak detector uses a very sensitive pickup which indicates the presence of Freon when placed below the leak: a white light illuminates or a warning buzzer sounds. It is easier to find a leak with the engine off, provided the pressure in the A/C system is 70-80 psi overall (slightly overcharged).

Always check for leaks with the engine off. The radiator fan of a running engine will circulate the refrigerant around making the leak point difficult to locate.

To check the evaporator, put the leak detector in the drain of the housing or in the center dash vent.

An R-134a leak detector has been tested and approved by BMW, TIF 5550. It automatically calibrates after it is turned on, and it detects leaks as small as 0.40 oz. of R-12 or R-134a per year.

BMW does not recommend the use of dyed refrigerant for finding a leak. The dyes can sometimes impair system operation and may damage the interior fabrics of the car.

TEMPERATURE SENSING EQUIPMENT

Correct climate control diagnosis requires an accurate and reliable temperature sensing device. A high quality analog thermometer or a digital pyrometer is recommended.

Typical Use: A/C Performance Quick Check

Test conditions = 90°F & 50% Humidity

Scheme 121

Scheme 122

Scheme 123

1. Note ambient temperature
2. Close all windows and doors.
3. Engine Speed = 1500-2000 RPM.
4. Blower Volume = Medium Speed
5. Temperature Wheel = "Max Cold
6. "Snowflake" Button = A/C On
7. Test conditions > 3 minutes
8. Center vent discharge = .20°F less than the ambient temperature.

DIS Temperature Probe

The Diagnosis and Information System (DIS) tester is equipped with a temperature sensor cable, stored in the compartment at the rear of the tester. It can be used to measure the temperatures of liquids and gasses from -20° to 200°C.

To use the DIS as a thermometer

Scheme 124

1. Select "Measurement System" button on the DIS start screen.
2. Select "Temperature C" button on the "Measuring System Multimeter" screen.

Cooling/Heat Gun

To simulate testing temperatures use the approved "Heating/Cooling Gun Kit"

Scheme 125

Scheme 126

The following safety precautions should be observed when working on an automotive refrigeration system

1. Always wear eye protection and gloves while handling refrigerant or servicing an air conditioning system.
2. Avoid breathing R-134a vapor or mist; exposure may irritate eyes, nose, throat, and lungs.
3. If refrigerant or compressor oil contacts the skin or eyes, rinse the affected area with warm water, administer first aid immediately, and consult a doctor.
4. Use only approved service equipment to discharge A/C systems.
5. If an accidental discharge occurs, ventilate the work area.
6. Store refrigerant service equipment and bulk supply containers in a cool, dry location away from direct sunlight and other heat sources (<113°F, (45°C)).
7. Do not expose refrigerants to an open flame, since burning refrigerant can produce poisonous gas. This includes open flames (such as in a propane leak detector), portable heaters, and lit cigarettes.
8. Do not pressure-test service equipment or vehicle A/C systems with an air/R- 134a mixture. Some mixtures of air and R-134a are combustible at elevated pressures. The use of compressed air for leak detection in an R-134a system could result in a fire or explosion. Do not discharge refrigerant into the atmosphere; contain it. R-134a is heavier than air; if discharged into the atmosphere, it can replace the air, causing suffocation. If R-12 is discharged into the air it damages the environment.
9. Never weld or steam-clean any part of the air conditioning system. Heating the refrigerant in a closed system could cause an explosion, due to the increased pressure.
10. Always consider R-12 or R-134a to be under high pressure, whether in the automobile refrigeration system, service equipment, or refrigerant storage containers.
11. R-134a should only be handled by competent, informed personnel using approved procedures and equipment. Failure to do so may result in serious injury and/or substantial equipment or vehicle damage.
12. Removal of R-134a must be carried out using R-134a equipment that meets the requirements of SAE J2210.
13. If accidental discharge occurs, ventilate the work area before resuming service. Exposure to high concentrations of refrigerant vapor can induce anesthetic effects such as weakness, dizziness, and nausea.

The R134a service fittings are a unique design and prohibit the connection of nonapproved equipment. The large diameter metric fitting is the high side (also sight glass) while the smaller diameter fitting is the low side.

Scheme 127

The ACR4 unit has approved quick disconnect hose connectors which correspond to the special R134a service fittings found on the vehicle. This arrangement prevents the accidental connection of R12 service equipment.

No attempt should ever be made to bypass these special fittings

Scheme 128

AMBIENT TEMPERATURE / RELATIVE HUMIDITY REFERENCE CHART

AMBIENT TEMPERATURE / RELATIVE HUMIDITY REFERENCE CHART

Complaint

Cooling is not adequate.

Scheme 129

1. The low-side gauge reading is low, or may go into a vacuum.
2. The high-side gauge reading increases as the system operates.
3. The discharge air from the evaporator is only slightly cool.
4. The expansion valve inlet may show heaving sweating or frost.
5. The high-pressure side is abnormally hot.

Diagnosis

1. The expansion valve is stuck closed; or is plugged by moisture, ice, or foreign material.

Correction

1. Recover the refrigerant from the system.
2. If the condition described on page 28 exist, replace the receiver/dryer.
3. Evacuate the system for a minimum of 30 minutes and recharge it. NOTE: Longer periods of applied vacuum are better.
4. Operate the system and check its performance.
5. If the system fails to function correctly, replace the expansion valve.

Cooling is not adequate.

Scheme 130

1. The low-side gauge reading is too high.
2. The high-side gauge reading is too low.
3. The sight glass is free of bubbles; the system is fully charged. (If equipped)
4. The discharge air from the evaporator is not sufficiently cool.

1. There may be a leak in the compressor, or the drivebelt may be loose/worn. The compressor pistons, rings, valves, or cylinders may be excessively worn or scored.

1. Check the compressor for noisy or knocking operation.
2. Recover the refrigerant from the system.
3. Remove and replace the compressor, if it is noisy/knocking.
4. Examine the condenser for metal fragments - clean if required.
5. Replace the receive/dryer.
6. Evacuate the system for a minimum of 30 minutes and recharge it. NOTE: Longer periods of applied vacuum are better.
7. Operate the system and check its performance.

Cooling is not adequate.

Scheme 131

1. The low-side gauge reading is excessively high.
2. The high-side gauge reading is excessively high.
3. Bubble may appear occasionally in the sight glass. (if equipped) The liquid line is very hot.
4. The discharge air from the evaporator is warm

Scheme 132

1. The system may be overcharged
2. The condenser may not be operating properly.
3. Air flow through the condenser may be poor.
4. The auxiliary fan may not be operating properly.

1. Recover the refrigerant.
2. Recharge the refrigerant according to the underhood label or the specifications in TIS.
3. Operate the system and check its performance.

If The Gauge Readings Are Still To High

1. Recover the refrigerant.
2. Blow shop air through the condenser to check whether its passages are free. A condenser can be clogged by debris, such as fragments from a failed compressor valve or desiccant from the receiver/dryer. If the condenser passages are clogged, replace it. Determine what material clogged the condenser.
3. Replace the receiver/dryer.
4. Evacuate the system for a minimum of 30 minutes and recharge it. NOTE: Longer periods of applied vacuum are better.
5. Operate the system and check its performance.

NON-APPROVED AIR CONDITIONING REFRIGERANTS

Recently, "alternative" refrigerants for automatic air conditioning have been marketed in certain areas. These refrigerants are claimed to be compatible replacements for the BMW approved R-12 refrigerant (also known as Freon). The "alternative" refrigerants usually consist of a mixture of various components; among then may be R-12, R-22, R-142b, R- 76, isobutance, propane or ammonia.

These refrigerant components are not related to, and not as ecologically sound as, the new R-134a refrigerant.

THIS TYPE OF "ALTERNATIVE" REFRIGERANTS IS NOT COMPATIBLE WITH, AND NOT APPROVED FOR USE IN BMW AIR CONDITIONING SYSTEMS.

Problems than can occur when charging a BMW air conditioning system with an alternative mix or "blend"

1. R-22 is incompatible with the existing R-12 desiccant found in BMW receiver-dryers. The desiccant will break down, and may be distributed through the A/C system, clogging the expansion valve and destroying the compressor. Some products use "sealants" which can clog orifices in both the vehicle and recycling equipment.
2. R-22 can result in substantially higher pressure when installed in a system designed for R-12, especially in stop-and-go traffic in high ambient temperatures.
3. Current R-12 hoses, O-rings and sealing materials found on BMW vehicles are not designed to, and do not, retain R-22. The R-22 permeates out of the hoses. If the R-12 is then lost from the system, the remaining R-142b is flammable.
4. If a vehicle with a non-approved refrigerant is brought into a shop and connected to recycling equipment, the same problems can occur with the recycling equipment. In addition, the "alternative" refrigerant can be passed on to other vehicles that are connected to the same recycling equipment. This could spread the problems to other vehicles.
5. Materials such as propane and isobutane are flammable. If the proper pressure and charge conditions are not maintained, these components "fractionate" out of the mixture. While the blended components may not be flammable, the individual components may be flammable if the mixture has fractionated
6. Automotive A/C systems are subject to Federal law, as well as specific state requirements. Currently, 10 states and the District of Columbia have enacted requirements that generally follow SAE definitions and requirements. The SAE J639 standard requires that "...Blend refrigerants, both in the original composition and in the compositions created as a result of normal mobile air-conditioning operating conditions, must meet the previous [ASHRAE 34-78] criteria: low toxicity, nonflammable, and nonexplosive requirements."
7. Blend refrigerants often require costly special processing to recycle. Since they cannot be vented to the atmosphere, servicing the system requires removal of the material into dedicated containers and shipping the material to a processing center for reclamation or destruction. The shipping must be done according to state and federal regulations, and the material is classified as a flammable gas for shipping purposes.

Solution

There are currently no BMW-approved alternative refrigerants to R-12 or R-134a .

Use of any refrigerant other than R-12 or R-134a will preclude warranty coverage of resulting failures.

Protect your customer's air conditioning systems as well as your own recycling equipment. Do not allow non-approved refrigerants to enter your recycling equipment.

If a customer has had air conditioning service performed elsewhere, determine that only approved refrigerant was used for recharging the system. This Service Information can be used to explain potential problems to customers.

When To Retrofit

As long as R-12 is available, it should be used to service a vehicle with an R-12 system. When R-12 supplies are unavailable, the customers may be willing to pay for a retrofit.

Standard Retrofit

Retrofit kits have been developed for the E31, E32, E34, and E36 models, to provide comparable system performance. The kits include a new receiver/ dryer, hoses, service fitting, refrigerant controls, and other parts.

VERIFIED SYSTEM MALFUNCTION FOLLOW-UP

After verifying that the complaint is actually a system malfunction, make the following "basic" checks

Visual Checks

1. Coolant level, coolant hoses in perfect condition and all drive belts tensioned properly.
2. A/C condenser, radiator, and system microfilters clean and unobstructed.
3. Auxiliary cooling fan operates with A/C on and rotates in the correct direction.
4. Interior flow-through ventilation functions correctly, vent flap valves behind rear bumper open with interior overpressure.

DIS Tester Checks

1. Instrument cluster temperature gauge and Engine Control Module temperature value indicate engine coolant temperature is normal.
2. IHKR/IHKA has no faults in memory and the system is not operating with stored substitute values.
3. Water valves open/close correctly, heater core temperature sensors indicate that the heater cores cool down on system cue.
4. Outlet flaps operate correctly, actual air discharge locations agree with tester indicated flap open/closed positions.
5. A/C compressor clutch energizes on system cue with engine running. (Many systems will not energize the compressor clutch with the ignition switched on, engine not running.)

See also:
• R-134A RECEIVER/DRYER