Climate Units - Design and Function (Coupe): Overview Volvo C70 I

Scheme 808

The control module has a built-in diagnostic system, the Volvo on-board diagnostic (OBD) system, which continuously monitors itself and its input and output signals.

Reading Control Module Identification

The Volvo Scan Tool (ST) identifies control modules by reading a code from the memory of the module. This code contains information about the control module part number.

Scheme 809

The control module has on-board diagnostics (OBD) which monitors input and output signals.

Reading Off Control Module Identification

The control module can be identified by reading off a code from the control module memory. This code contains information about the control module P/N.

Cooling Process (Overview)

Contained system

The main components in the system are: evaporator - receiver drier - compressor - condenser - choke valve. The components are connected to each other by pipes and/or hoses.

The system is filled with a suitable quantity of refrigerant and oil. The role of the oil is to lubricate and seal (piston-cylinder) the compressor.

Because it is the refrigerant that draws the oil around the system, a lack of refrigerant can result in noise from the compressor or cause the compressor to break down due to a lack of oil.

It is important that the system is used regularly. This is so that

1. the compressor is kept lubricated.
2. the refrigerant circulates so that moisture (water) that diffuses into the system (= forces in through the hoses etc.) can be taken up by the drying agent in the receiver dryer.

Evaporator

The evaporator is located in the climate control system's passenger compartment unit and the blower fan blows air through the evaporator.

In the evaporator there is a low pressure due to the choke valve and the suction effect of the compressor.

When the refrigerant enters the evaporator via the choke valve, it expands and both its pressure and temperature lower. The refrigerant then begins to boil and evaporate. The heat (energy) used for evaporation is taken from the air that is cooled.

When the warm air encounters the cold evaporator, the humidity condenses on the evaporator. The heat (energy) that is released during condensation is transferred to the refrigerant which evaporates. The temperature difference between the air and the refrigerant reduces. High humidity results in an increased need for cooling.

To obtain sufficient cooling capacity, the refrigerant's evaporation temperature must be considerably lower than the temperature desired in the passenger compartment. But to prevent the moisture that has condensed on the evaporator from freezing to ice, the air is not cooled below approximately +30°C (86°F) (at which stage the temperature of the refrigerant in the evaporator is approximately -30°C (-22°F)).

Receiver drier

Receiver drier

1. contains a drying agent that collects and binds moisture (water) in the system.
2. stores refrigerant in the system which is temporarily not needed.
3. separates refrigerant into gas form and liquid form.

The receiver drier is located on either the low pressure or the high pressure side, depending on the type of system (= type of choke valve).

Compressor

Compressor

1. sucks refrigerant in gas form from the evaporator.
2. compresses the gas thereby increasing its pressure and temperature.
3. expels the gas with high pressure and temperature to the condenser.

The compressor is mechanical and is driven by the car engine. When the compressor is operating it "steals" 0.5-8 kW (0.7-11 bhp) from the engine. This may be noticed as slight jerks when driving as the compressor is engaged/disengaged.

Condenser

The condenser is located in front of the engine radiator and charge air cooler (CAC) if installed. The breaking wind and engine cooling fan (FC) blow air through the condenser.

When the refrigerant enters the condenser it is in gas form and has both high pressure and temperature.

In the condenser the hot refrigerant loses some of its heat to the cooler air. The refrigerant then condenses and changes into liquid form.

The amount of heat given off = the amount of heat taken up in the evaporator + the amount of heat supplied by the compressor.

In order to supply sufficient cooling capacity, the condensation temperature of the refrigerant must be greater than the temperature of the outside air.

Choke valve

Upstream of the choke valve is the refrigerant in liquid form at high pressure.

The choke valve ensures that the correct amount of refrigerant is released to the evaporator. The quantity of refrigerant must be sufficient that the final remains evaporate precisely before the evaporator outlet. Too little refrigerant the refrigerant evaporates quickly and the steam is super heated = reduced cooling capacity. Too much refrigerant some of the refrigerant does not evaporate but is merely heated up = reduced cooling capacity. In addition there is the risk that some of the refrigerant in liquid from reaches the compressor. This may damage the compressor because liquid cannot be compressed.

The choke valve consists of an expansion pipe or a TEV valve (thermostatic Expansion Valve) depending on the type of system.

Pressure and temperature in the air conditioning system

1. The values may vary depending on the type of system, operational conditions etc.
2. The values listed below are only intended to give an indication of size.
3. Downstream of the evaporator gas form, 1.6-3.5 bar; -2 to -12°C (28 to 10°F).
4. Downstream of the compressor, upstream of the condenser gas form, 10-28 bar; +65 to +120°C (+149 to +248°F).
5. Downstream of the condenser, upstream of the choke valve liquid form, 9-24 bar; +40 to +80°C (+104 to +176°F).
6. Directly downstream of the choke valve partly in liquid form, 1.5-3.2 bar; -4 to -10°C (25 to 14°F).

Scheme 810

Hoses, pipes

All connections have O-rings as seals. The O-rings are manufactured in a specially developed material (HNBR = hydrated nitrile rubber). The O-rings are in different colors (black - blue - yellow - green) depending on the type of refrigerant they are suited to.

There are three different types of connection depending on the connection and the car and model year.

1. A: Connection with cap nut
2. B: Block connection
3. C: Quick-release connector (a special tool is required to separate the connection) The plastic ring hanging on one of the pipes shows that the connection is correctly assembled. At fist the ring is located in one section of the connection but that jumps free when the connection is pressed together with the correct force.

Evaporator (air heated heat exchanger)

Available in different versions depending on the car and model year. However the version that is used has nothing to do with the type of system the car has.

In principle it consists of pipe loops in which the refrigerant flows. The loops have flanges to increase the heat absorbing surface.

Condenser (air cooled heat exchanger)

Available in different versions depending on the car and model year. However the version that is used has nothing to do with the type of system the car has.

In principle it consists of pipe loops in which the refrigerant flows. The loops have flanges to increase the heat radiating surface.

There are two main types - serial and parallel. Serial = one, two or three pipes that run forwards and backwards through the condenser (the loops are in series).

Parallel = several pipes ("flat pipes") which run parallel through the condenser. Each pipe has a large number of channels and the pipes are connected together at the face of the condenser.

Receiver drier

In principle it is a reservoir containing a drying agent.

The internal design with piping depends on the system it is intended for. On systems with a TEV valve there is a filter in the receiver drier. The filter collects any impurities in the system.

On systems with an expansion pipe, the corresponding filter is integrated with the expansion pipe.

Compressor

There are a number of different makes and versions depending on the engine variant and the car and model year.

The different versions are

1. wing compressor.
2. piston compressor with 2 - 4 - 5 - 6 or 7 cylinders.
3. piston compressor with fixed or variable cylinder displacement.

This is mechanical and is belt driven by the engine.

Has an electro-magnetic clutch which makes it possible to engage/disengage the compressor.

Electro-magnetic clutch

The clutch consists of

1. a solenoid coil mounted directly on the compressor housing.
2. a flexible plate mounted on the compressor shaft.
3. a pulley positioned on the front face of the compressor.

When the compressor is disconnected the pulley rotates freely without effecting the compressor.

When the solenoid coil is supplied with current the flexible plate is drawn into contact with the pulley.

Power is transferred from the pulley via the plate to the compressor shaft.

The way in which the engagement/disengagement (the current to the solenoid coil) is governed varies depending on type of system, engine variant and the car and model year.

Scheme 811

The pistons are driven by a cam pulley, the angle of which can vary.

When the compressor is disengaged, the angle is determined by the springs.

When the compressor is engaged, the angle is determined by the pressure affecting the top side of the pistons (= intake pressure) and lower side (= pressure in the crank case) during the intake phase.

The pressure on the lower side of the pistons (= in the crank case) is governed by a valve which keeps the intake pressure constant.

High intake pressure = large cylinder displacement

The valve opens and lowers the pressure in the crank case. The back pressure on the reverse of the pistons is then reduced and the angle of the cam pulley increases.

An increased angle gives an increased cylinder stroke which results in a greater volume of refrigerant being sucked in and the outlet pressure dropping.

Low intake pressure = small cylinder displacement

The valve closes and the pressure in the crank case increases. The pressure is built up by the refrigerant which is led via a calibrated channel from the outlet side to the crankcase.

The back pressure on the reverse of the pistons is then increased and the angle of the cam pulley reduces.

A reduced angle gives an reduced cylinder stroke which results in a smaller volume of refrigerant being sucked in and the outlet pressure increasing.

The advantages of this type of compressor are

The flow of refrigerant is continually adapted to requirements.

Few engagements/disengagements providing good driving comfort.

Scheme 812

Expansion Pipe ("orifice")

Passive flow regulator (= fixed choke valve).

Consists of a thin metal pipe which is positioned in a plastic housing with a filter on both the intake and outlet sides. The filter collects any impurities in the system. Passive flow regulator (= fixed choke valve).

Governs the volume of refrigerant which is released from the evaporator.

The volume is affected by the dimensions of the pipe (diameter, length) and the pressure and temperature on both sides of the pipe.

The pipe is adjusted for its system and for the type of refrigerant that is used.

The pipe for the R12 has a greater diameter than the pipe for the R134a. This is because the R12 and oil mixture has a higher viscosity than the oil and R134a mixture.

Governs the system's capacity and functions as an anti-freeze

Consists of a switch which is affected by the pressure of the refrigerant downstream of the evaporator, in other words on the lower pressure side (the pressure switch (Pressostat) must be positioned as close to the evaporator outlet as possible.

If the pressure is too low (= too low temperature the pressure switch (Pressostat) interrupts a current circuit and the compressor is switched off. This is so that the water that condenses on the evaporator does not freeze to ice and obstruct the airflow through the evaporator. Heavy build up of ice can also cause damage to the evaporator.

When the pressure (= temperature) increases again, the pressure switch (Pressostat) closes the current circuit and the compressor is engaged.

The pressure switch (Pressostat) opens at approximately 1.6 bar and closes at approximately 3.2 bar.

Receiver drier

On systems with an expansion pipe, the pipe may in some cases allow through a little too much refrigerant. The result is that a little of the refrigerant will be released from the evaporator in liquid form. To prevent damage to the compressor, the receiver drier must be positioned on the low pressure side and be able to separate liquid from gas.

The receiver drier outlet is located so that only refrigerant in gas form can leave the receiver drier. Refrigerant in liquid form is collected in the bottom of the receiver drier.

The refrigerant in the bottom of the receiver drier contains a relatively high amount of oil. This mixture (refrigerant and oil) is led through a calibrated hole out into the outlet pipe and is transferred with the gas back to the compressor.

The hole plays a very important role in the return of oil to the compressor.

Control of the temperature in the passenger compartment

The air conditioning system has only two positions, off and on.

If it is too cold in the passenger compartment, the temperature can be controlled with the normal heat and blower fan controls.

Service socket

On systems with an expansion pipe, there is often only one nipple (on the low pressure side) to which the A/C station or pressure gauge can be connected.

Scheme 813

TEV Valve

Active flow regulator (= variable choke valve).

Consists of

1. a valve which is affected by a spring and a membrane.
2. A capillary pipe with a resistor positioned on the evaporator outlet pipe.
3. The position of the resistor has been carefully tested.
4. The capillary pipe is filled with refrigerant.
5. a pressure equalization pipe is connected to the evaporator outlet pipe.

Governs the volume of refrigerant which is released from the evaporator.

Too little refrigerant = the temperature at the outlet pipe increases the refrigerant in the capillary pipe expands and exerts pressure on the membrane the valve is opened and releases more refrigerant to the evaporator.

Too much refrigerant = the temperature at the outlet pipe falls the refrigerant in the capillary pipe reduces in volume the spring presses the valve back the valve is shut and releases less refrigerant to the evaporator.

The temperature and pressure in the system are related to each other. Assumes that there is a drop in pressure in the evaporator, in which case the temperature at the outlet pipe also falls. This means that the valve is closed and there will be too little refrigerant - the capacity reduces. The pressure in the outlet pipe is led via a pressure equalization pipe to the underside of the membrane and compensates for any fall in pressure.

The TEV valve is carefully adapted for its system and for the type of refrigerant that is used.

The valve is calibrated to release through exactly the correct amount of refrigerant which can be evaporated completely and to keep the amount of super heating to a minimum (super heating is normally approximately 6-10°C (43-50°F). This is to obtain maximum cooling capacity and to prevent refrigerant in liquid form leaving the evaporator and reaching the compressor.

Freeze protection

Thermostat with capillary pipes or a temperature sensor depending on the car and model year.

Positioned where the evaporator is coldest (where frost forms first) The location is extremely important and is often tested manually.

The thermostat/pressure sensor interrupts a current circuit and disengages the compressor when the temperature becomes too low. This is so that the water that condenses on the evaporator does not freeze to ice and obstruct the airflow through the evaporator. Heavy build up of ice can also cause damage to the evaporator.

When the temperature increases again, the thermostat/temperature sensor closes the current circuit and the compressor is engaged.

The thermostat/temperature normally opens at approximately 2°C (36°F) and closes at approximately 6°C (43°F).

Receiver drier

The function of the TEV valve can be interfered with by gas bubbles in the refrigerant. Therefore the receiver drier must be positioned on the high pressure side and be able to separate gas from liquid.

The receiver drier outlet is located so that only refrigerant in liquid form can leave the receiver drier.

Refrigerant in gas form is collected in the top of the receiver drier. When the heat is transferred, the refrigerant will also condense.

There is a filter in the receiver drier which collects any impurities in the system.

Control of the temperature in the passenger compartment

Certain cars have an adjustable thermostat which can be adjusted for the evaporator temperature at which the compressor will be disconnected.

The maximum position (marked red) should however only be used briefly after start to rapidly lower the temperature in the passenger compartment, and if applicable in dry desert climates. Otherwise there is a risk that the condensation will freeze to is.

On most cars the air conditioning has only two positions, off and on.

If it is too cold in the passenger compartment, the temperature can be controlled with the normal heat and blower fan controls.

Service socket

On systems with a TEV valve, there is two nipples (one on the high pressure side and one on the low pressure side) to which the A/C station or pressure gauge can be connected.

Scheme 814

Which functions/components there are, how they are designed and where they are located depends on the type of system, car and model year and the engine variant.

Pressure switches

Are located on the high pressure side and in principle consist of switches which open/close a current circuit or a pressure sensor which transmits a signal to the engine control module (ECM).

These can be

1. A: A linear pressure sensor. In this case, all the functions are always governed via the engine control module (ECM) and the current pressure can be read off using the Volvo Scan Tool (ST). There tasks are: to start the engine cooling fan (FC) at 1st or 2nd speeds at high pressure. The air flow through the condenser is then increased. More heat can be given off by the refrigerant to the air, the temperature/pressure drops and the capacity is maintained. to disengage the compressor if the pressure falls too low (= safety switch), in the event of leakage for example. to disengage the compressor if the pressure rises too much (= safety switch), if the pressure switch or engine cooling fan (FC) is not functioning for example.
2. B: Separate units. There tasks are: to start the engine cooling fan (FC) at 1st or 2nd speeds at high pressure. The air flow through the condenser is then increased. More heat can be given off by the refrigerant to the air, the temperature/pressure drops and the capacity is maintained. to disengage the compressor if the pressure falls too low (= safety switch), in the event of leakage for example. to disengage the compressor if the pressure rises too much (= safety switch), if the pressure switch or engine cooling fan (FC) is not functioning for example.
3. C: A combined unit with multiple integrated pressure switches. There tasks are: to start the engine cooling fan (FC) at 1st or 2nd speeds at high pressure. The air flow through the condenser is then increased. More heat can be given off by the refrigerant to the air, the temperature/pressure drops and the capacity is maintained. to disengage the compressor if the pressure falls too low (= safety switch), in the event of leakage for example. to disengage the compressor if the pressure rises too much (= safety switch), if the pressure switch or engine cooling fan (FC) is not functioning for example.

On the majority of pressure switches from and including 1992 model years there is a valve case (Schraeder valve) in the connection. This enables the pressure switches to be removed without needing to drain the system.

Note. If the connection has internal threads (as at C in the illustration) there is no valve casing.

Safety Valve

Is located on the high pressure side, on the compressor or on a pipe.

The valve opens and releases refrigerant if the pressure is too high in the system. It then shuts again when the pressure has returned to normal.

This function protects the system from exploding if, for example, the safety switch is not functioning.

Temperature switch

Is located on and gauges the compressor temperature.

Opens the compressor current circuit at approximately 105°C (221°F). Closes the circuit when the temperature has fallen to approximately 90°C (194°F).

This function protects the compressor from overheating/breakdown in the event of, for example, refrigerant leakage (= low quantity).

Other functions that may be present

The compressor can be engaged 10 seconds after the engine is started at the earliest.

Often governed by a timer circuit in the A/C relay or in the engine control module (ECM).

This function prevents the engine stopping immediately after start. The engine is subjected to a heavy load when the compressor engages.

Disengagement of the compressor at

1. wide open throttle (WOT) (often time governed disengagement).
2. heavy acceleration and low speed (usually occurs on diesel engines).
3. high engine coolant temperature.

Usually governed via the engine control module (ECM).

These functions are to provide optimal acceleration and to prevent the engine from overheating.

Values for pressure switches/safety switch/safety valve

The values vary depending on, amongst other things, the type of system, refrigerant and compressor.

The following values are only an example. They apply to a Volvo 900 with R134a refrigerant and Sanden SD-7H15 compressor.

1. The engine cooling fan (FC) low speed is engaged at 18 bar and disengages at 14 bar.
2. The engine cooling fan (FC) high speed is engaged at 23 bar and disengages at 19 bar.
3. The compressor disengages at 30 bar and engages at 20 bar.
4. The safety valve opens at 38 bar.

Scheme 815

The current circuit for the compressor (engagement/disengagement) varies greatly depending on the type of system, engine variant and the car and model year.

The circuit may be very simple with few components or more complex with many components.

Example 1

The example shows the circuit on a 1977 Volvo 240.

The circuit includes

1. a switch to manually engage/disengage the compressor.
2. a thermostat governed switch.

The thermostat senses the temperature at the evaporator via a resistor.

At too low temperatures (= risk of ice formation) the switch opens and the compressor is disengaged

When the temperature increases the switch closes again and the compressor is engaged.

Scheme 816

1. Compressor
2. Air conditioning (A/C) relay
3. Engine control module (ECM)
4. Air conditioning (A/C) pressure sensor
5. Engine coolant temperature sensor
6. Throttle position (TP) sensor
7. Air conditioning (A/C) pressure switch (Pressostat)
8. Control module ECC
9. Passenger compartment temperature sensor
10. Outside pressure sensor
11. Engine coolant temperature sensor ECC
12. Sun sensor

Example 2

The example shows the circuit on a 1996 Volvo 960 with Motronic 4.4 and ECC.

The compressor is governed via a relay by the engine control module (ECM) depending on a number of input signals. With this connection the engine control module (ECM) can quickly (in advance) compensate for the changes in load that occur when the compressor is engaged and disengaged (= less jerkiness).

Function

The ECC control module calculates whether the compressor needs to be engaged to obtain the correct temperature in the passenger compartment. The calculations are based on the drivers requirements (= the settings of the control) and signals from a number of sensors.

If necessary, the control module transmits a signal (= requests engagement of the compressor).

The signal is sent to the engine control module (ECM) via the pressure switch (Pressostat).

The pressure switch (Pressostat) breaks the circuit if the pressure and therefore the temperature in the system (on the low pressure side) falls too low.

The engine control module (ECM) activates the A/C relay and the compressor is engaged.

(10 seconds after the start of the engine at the earliest - timer circuit in the control module).

The engine control module (ECM) disengages the compressor

1. when the request to engage from the ECC control module/pressure switch (Pressostat) ceases.
2. at wide open throttle (WOT), for a maximum of 15 seconds (signal from the throttle position (TP) sensor).
3. at high engine coolant temperature (ECT), above approximately 125°C (257°F) signal from the temperature sensor).
4. at too high-pressure on the high pressure side, above approximately 30 bar (signal from pressure sensor).

The signals from the engine coolant temperature sensor and the pressure sensor are also used by the engine control module (ECM) to govern the engine cooling fan (FC).

Scheme 817

Main Air Conditioning System Components (Overview)

There are five main components in the system

1. evaporator
2. receiver drier
3. compressor
4. condenser
5. choke valve.

The system is filled with a suitable quantity of refrigerant and oil.

The system has both a low and high pressure side. These are divided by the compressor and the choke valve.

The evaporator is located on the low pressure side and the condenser is on the high pressure side.

The air conditioning system functions only at outside temperatures above approximately 0-5°C (32-41°F) (varies depending on the type of system). At lower temperatures the pressure in the system is too low and the compressor is not engaged.

Evaporator (=air heated heat exchanger)

In the evaporator the heat is transferred from the warm air (the heat is "cooled") to the cold refrigerant.

The refrigerant then begins to boil and is converted to gas form (evaporates).

The blower fan increases the air flow through the evaporator.

Note. In most systems, the blower fan must be operating before the air conditioning system can be engaged.

Receiver drier

The receiver drier has a number of tasks, such as collecting and binding the moisture (water) in the system.

The receiver drier is located on either the low pressure or the high pressure side, depending on the type of system.

Compressor

Sucks refrigerant in gas form from the evaporator.

Compresses the refrigerant thereby increasing its pressure and temperature. The heated refrigerant in gas form passes on to the condenser.

Condenser (= air cooled heat exchanger)

At the condenser, the heat is transferred from the refrigerant to the colder outside air.

The refrigerant then condenses and changes into liquid form.

In most systems there is an electrical fan which increases the air flow through the condenser. This increases the transfer of heat from the refrigerant to the outside air. This of course also increases the capacity of the air conditioning system.

Choke valve

Downstream of the choke valve is the refrigerant in liquid form at high pressure.

The choke valve regulates the amount of refrigerant that flows into the evaporator.

Scheme 818

The control module ID can be confirmed by reading off a code from the control module memory.

This code contains information about the control module P/N.

Scheme 819

The timer has an integrated diagnostic system, Volvo on-board diagnostic (OBD) system, which constantly supervises the timer and the in and out signals.