HVAC - Service Information: Overview Dodge Dakota III

OPERATION

The heating-A/C system used in this vehicle is a single zone, blend-air type system. In this blend-air heating-A/C system, two blend-air doors control the amount of conditioned air that is allowed to flow through, or around, the heater core. A temperature control determines the discharge air temperature by operating an electric actuator, which operates the blend-air doors. This allows an almost immediate control of the output air temperature of the system. The A/C system is designed for the use of non-CFC, R-134a refrigerant and uses an A/C evaporator to cool and dehumidify the incoming air prior to blending it with the heated air.

Scheme 1

The heating-A/C system pulls outside (ambient) air through the cowl opening at the base of the windshield, then into the air inlet housing and through the A/C evaporator (3). Air flow can be directed either through or around the heater core (1). This is done by adjusting the blend-air doors (2) with the temperature controls located on the A/C-heater control in the instrument panel. The air flow can then be directed from the panel, floor and defrost outlets in various combinations using the mode control located on the A/C-heater control. Air flow velocity can be adjusted with the blower speed control located on the A/C-heater control.

The outside (fresh) air intake can be shut off by selecting the Recirculation Mode with the mode control. This will operate an electrically actuated recirculation-air door (4) that closes off the fresh air intake and recirculates the air that is already inside the vehicle.

The A/C compressor can be engaged in any mode by pressing the snowflake, A/C on/off button. It can also be engaged by placing the mode control in the mix to defrost positions. This will remove heat and humidity from the air before it is directed through or around the heater core. The mode control on the A/C-heater control is used to also direct the conditioned air to the selected system outlets. The mode control uses two electric actuators to control the mode-air doors (5 and 6).

The defroster outlet receives airflow from the HVAC housing through the molded plastic defroster duct, which connects to the HVAC housing defroster outlet. The airflow from the defroster outlet is directed by fixed vanes in the defroster outlet grille and cannot be adjusted. The defroster outlet grille is serviceable from the instrument panel.

The side window demister outlets receive airflow from the HVAC housing through the molded plastic demister ducts. The demisters direct air from the HVAC housing through the outlets located on the top corners of the instrument panel. The demisters operate when the mode control is positioned in the bi-level, floor, floor-defrost and defrost settings. The airflow from the side window demister outlets is directed by fixed vanes in the demister outlet grilles and cannot be adjusted. The demister outlet grilles are only serviced with the instrument panel outlets.

The instrument panel outlets receive airflow from the HVAC housing through a molded plastic center distribution duct, center panel duct and two end panel ducts. The two end panel ducts direct airflow to the left and right instrument panel outlets, while the center panel duct directs airflow to the two center panel outlets. Each of these outlets can be individually adjusted to direct the flow of air.

The floor outlets receive airflow from the HVAC housing through the floor distribution duct. The front floor outlets are integral to the molded plastic floor distribution duct, which is secured to the bottom of the HVAC housing. The floor outlets cannot be adjusted.

Note. It is important to keep the air intake opening clear of debris. Leaf particles and other debris that is small enough to pass through the cowl opening screen can accumulate within the HVAC housing. The closed, warm, damp and dark environment created within the housing is ideal for the growth of certain molds, mildews and other fungi. Any accumulation of decaying plant matter provides an additional food source for fungal spores, which enter the housing with the fresh intake-air. Excess debris, as well as objectionable odors created by decaying plant matter and growing fungi can be discharged into the passenger compartment during heater-A/C operation if the air intake opening is not kept clear of debris.

This A/C system uses an A/C orifice tube to meter the flow of refrigerant to the A/C evaporator. The A/C evaporator cools and dehumidifies the incoming air prior to blending it with the heated air. To maintain minimum evaporator temperatures and prevent evaporator freezing, an evaporator temperature sensor is used. The sensor is located downstream of the A/C evaporator and supplies an evaporator temperature signal to the A/C-heater control. The A/C-heater control broadcasts the A/C request on the controller area network (CAN) B bus, where it is read and processed by the front control module (FCM), which in turn broadcasts it on the CAN C bus, where it is read and processed by the powertrain control module (PCM) which cycles the A/C clutch relay as necessary.

The blend door actuator is connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the HVAC wire harness. The blend door actuator can move the blend-air doors in two directions. When the A/C-heater control pulls the voltage on one side of the motor connection high and the other connection low, the blend-air doors will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the blend-air doors moves in the opposite direction.

When the A/C-heater control makes the voltage to both connections high or both connections low, the blend-air doors stop and will not move. The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the blend door actuator and the blend-air doors. The A/C-heater control learns the blend-air doors stop positions during the calibration procedure and will store a diagnostic trouble code (DTC) for any problems it detects in the blend door actuator circuit.

The blend door actuator is diagnosed using the scan tool. Refer to HVAC - ELECTRICAL DIAGNOSTICS for more information.

The blend door actuator cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

DESCRIPTION

The two mode door actuators (1) are reversible, 12-volt direct current (DC), servo motors. The mode door actuators are located on the driver side of the HVAC housing. The mode door actuators are mechanically connected to the floor/defrost and the panel-air doors. The mode door actuators are interchangeable with the actuators for the blend-air doors and the recirculation-air door. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle (2). Each actuator also has an identical output shaft with splines (3) that connects it to its respective door linkage and three integral mounting tabs (4) that allow the actuator to be secured to the HVAC housing. The mode door actuators do not require mechanical indexing to the mode-air doors, as they are electronically calibrated by the A/C-heater control.

The two mode door actuators can be serviced from underneath the drivers side of the instrument panel.

Both the floor/defrost actuator and the panel door actuator (mode door actuators) are connected to the A/C-heater control through the vehicle electrical system by dedicated two-wire leads and connectors of the HVAC wire harness. Each mode door actuator can move the floor/defrost or the panel-air doors in two directions. When the A/C-heater control pulls the voltage on one side of an actuator motor connection high and the other connection low, the respective mode-air door will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the mode-air door moves in the opposite direction.

When the A/C-heater control makes the voltage to both connections high or both connections low, the respective mode-air door stops and will not move. The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of both mode door actuators and the mode-air doors. The A/C-heater control learns the mode-air door stop positions during the calibration procedure and will store a diagnostic trouble code (DTC) for any problems it detects in the mode door actuator circuits.

The mode door actuators are diagnosed using a scan tool. Refer to HVAC - ELECTRICAL DIAGNOSTICS for more information.

The mode door actuators cannot be adjusted or repaired and, if faulty or damaged, they must be replaced.

The recirculation door actuator (1) is a reversible, 12 volt direct current (DC), servo motor. The recirculation door actuator is located on the left side of the HVAC air inlet housing. The recirculation door actuator is interchangeable with the actuators for the blend-air doors and the mode-air doors. Each actuator is contained within an identical black molded plastic housing with an integral wire connector receptacle (2). Each actuator also has an identical output shaft with splines (3) that connects it to its door linkage and three integral mounting tabs (4) that allow the actuator to be secured to the air inlet housing. The recirculation door actuator does not require mechanical indexing to the recirculation-air door, as it is electronically calibrated by the A/C-heater control.

The recirculation door actuator can be accessed for serviced by removing the air inlet housing.

The recirculation door actuator is connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the HVAC wire harness. The recirculation door actuator can move the recirculation-air door in two directions. When the A/C-heater control pulls the voltage on one side of the motor connection high and the other connection low, the recirculation-air door will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the recirculation-air door moves in the opposite direction.

When the A/C-heater control makes the voltage to both connections high or both connections low, the recirculation-air door stops and will not move. The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the recirculation door actuator and the recirculation-air door. The A/C-heater control learns the recirculation-air door stop positions during the calibration procedure and will store a diagnostic trouble code (DTC) for any problems it detects in the recirculation door actuator circuits.

The recirculation door actuator cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The recirculation door actuator is diagnosed using a scan tool. Refer to HVAC - ELECTRICAL DIAGNOSTICS for more information.

The A/C compressor clutch components provide the means to engage and disengage the A/C compressor from the engine accessory drive belt. When the electromagnetic A/C clutch field coil is energized, it magnetically draws the clutch plate into contact with the clutch pulley and drives the compressor shaft. When the coil is not energized, the pulley freewheels on the clutch hub bearing, which is part of the pulley assembly.

The A/C compressor clutch engagement is controlled by the following components

1. A/C-heater control in the passenger compartment
2. A/C pressure transducer on the A/C liquid line
3. Powertrain control module (PCM) in the engine compartment
4. A/C clutch relay in the power distribution center (PDC)

The A/C compressor clutch components cannot be repaired and, if faulty or damaged, they must be replaced.

The ISO-standard A/C clutch relay is an electromechanical switch that uses a low current input controlled by the powertrain control module (PCM) to control the high current output to the A/C clutch field coil. The movable, common feed relay contact is held against the fixed, normally closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it draws the movable common feed relay contact away from the fixed, normally closed relay contact and, holds it against the fixed, normally open relay contact. This action allows high current to flow to the A/C clutch field coil.

When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, normally closed contact point. The resistor or diode is connected in parallel with the relay coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The A/C clutch relay terminals are connected to the vehicle electrical system through a receptacle in the integrated power module (IPM). The inputs and outputs of the A/C clutch relay include

1. The common feed terminal (30) receives fused battery current through a B(+) circuit at all times.
2. The coil ground terminal (85) receives a ground input from the PCM through the A/C clutch relay control circuit only when the PCM electronically pulls the control circuit to ground.
3. The coil battery terminal (86) receives fused battery current an ignition switch output (Run) circuit only when the ignition switch is in the On position.
4. The normally open terminal (87) provides a battery current output to the A/C clutch coil through the A/C clutch relay output circuit only when the compressor clutch relay coil is energized.
5. The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the A/C clutch relay coil is de-energized.

The A/C clutch relay cannot be repaired and, if faulty or damaged, it must be replaced. Refer to the appropriate wiring information for diagnosis and testing of the ISO-standard relay and for complete HVAC wiring diagrams.

The blower motor resistor is connected to the vehicle electrical system through a dedicated wire lead and connector of the HVAC wire harness. The blower motor resistor has multiple resistor wires, each of which will reduce the current flow through the blower motor to change the blower motor speed.

The blower motor control in the MTC heating-A/C system directs the ground path for the blower motor through the correct resistor wire to obtain the selected speed. With the blower motor control in the lowest speed position, the ground path for the blower motor is applied through all of the resistor wires. Each higher speed selected with the blower motor control applies the blower motor ground path through fewer of the resistor wires, increasing the blower motor speed.

The blower motor resistor cannot be adjusted or repaired and, if faulty or damaged (such as a cracked ceramic heat sink), it must be replaced.

The ambient air temperature sensor is a variable resistor that operates on a ground circuit and a 5-volt reference signal circuit sent by the front control module (FCM) through a two-wire lead and connector of the vehicle wire harness. The ambient air temperature sensor changes its internal resistance in response to changes in the outside air temperature, which either increases or decreases the reference signal voltage read by the FCM. The FCM converts and broadcasts the sensor data over the controller area network (CAN) B bus, where it is read by the A/C-heater control and other various vehicle control modules.

The ambient air temperature sensor is diagnosed using the scan tool. Refer to appropriate Engine ELECTRICAL DIAGNOSTICS article for more information.

The ambient air temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

Scheme 2

1. Disconnect and isolate the negative battery cable.
2. Disconnect the wire harness connector (1) from the ambient air temperature sensor (2).
3. Remove the bolt (3) that secures the ambient air temperature sensor to the front bumper beam (4) and remove the sensor.

The evaporator temperature sensor monitors the surface temperature of A/C evaporator and supplies an input signal to the A/C-heater control. The A/C-heater control uses the evaporator temperature sensor input signal to optimize A/C system performance and to protect the A/C system from evaporator freezing. The evaporator temperature sensor will change its internal resistance in response to the temperatures it monitors and is connected to the A/C-heater control through sensor ground circuit and a 5-volt reference signal circuit. As the temperature of the A/C evaporator decreases, the internal resistance of the evaporator temperature sensor decreases.

The A/C-heater control uses the resistance reading as an indication that conditions are correct to broadcast an A/C request message on the controller area network (CAN) B bus, where it is read by the front control module (FCM). The FCM then requests the powertrain control module (PCM) to cycle the A/C compressor clutch as necessary over the CAN C bus.

The evaporator temperature sensor is diagnosed using a scan tool. Refer to HVAC - ELECTRICAL DIAGNOSTICS for more information.

The evaporator temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

The A/C pressure transducer monitors the pressures in the high side of the refrigerant system through its connection to a fitting on the A/C liquid line. The A/C pressure transducer will change its internal resistance in response to the pressures it monitors. A Schrader-type valve in the liquid line fitting permits the A/C pressure transducer to be removed or installed without disturbing the refrigerant in the A/C system.

The front control module (FCM) provides a five volt reference signal to the A/C pressure transducer, then monitors the output voltage of the A/C pressure transducer on a sensor return circuit to determine refrigerant pressure. The FCM broadcasts a refrigerant pressure message to the PCM, which is programmed to respond to the A/C pressure transducer and other sensor inputs by controlling the operation of the A/C compressor clutch to help optimize A/C system performance and to protect the system components from damage. The PCM will disengage the A/C compressor clutch when high side pressure rises above 3172 kPa (460 psi) and re-engage the clutch when high side pressure drops below 1999 kPa (290 psi). The A/C pressure transducer will also disengage the A/C compressor clutch if the high side pressure drops below 193 kPa (28 psi) and will re-engage the clutch when the high side pressure rises above 234 kPa (34 psi). The A/C pressure transducer message to the PCM will also prevent the A/C compressor clutch from engaging when ambient temperatures are below about 4.5° C (40° F) due to the pressure/temperature relationship of the refrigerant.

The A/C pressure transducer is diagnosed using a scan tool. Refer to appropriate Engine ELECTRICAL DIAGNOSTICS article for more information.

The A/C pressure transducer cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

All models are equipped with a common HVAC housing assembly (1) that combines A/C and heating capabilities into a single unit mounted within the passenger compartment. The HVAC housing consists of the following

1. HVAC housing - The HVAC housing consists of an upper housing and a lower housing that are attached together by screws and metal retaining clips and is mounted to the dash panel behind the instrument panel. The HVAC housing contains the heater core (2), blend-air doors and actuator (3), A/C evaporator (4), blower motor (7), evaporator temperature sensor (8), mode-air doors and actuators (9), floor distribution duct, foam seals and the HVAC wire harness.
2. Air inlet housing - The air inlet housing is mounted to the right end of the HVAC housing and contains the blower motor resistor (5) and the recirculation-air door and actuator (6).

The heating-A/C system is a blend-air type system. The two blend-air doors control the amount of conditioned air that is allowed to flow through, or around, the heater core. This single zone heating-A/C system uses only one blend door actuator.

The A/C system is designed for the use of a non-CFC, R-134a refrigerant and uses an A/C evaporator to cool and dehumidify the incoming air prior to blending it with the heated air. A temperature control determines the discharge air temperature by operating the blend door actuator, which moves the blend-air doors. This allows an almost immediate control of the output air temperature of the system. The two mode door actuators operate the mode-air doors which direct the flow of the conditioned air out the various air outlets, depending on the mode selected. The recirculation door actuator operates the recirculation-air door which closes off the fresh air intake and recirculates the air already inside the vehicle. The electric door actuators are connected to the vehicle electrical system by the HVAC wire harness. The blower motor controls the velocity of air flowing through the HVAC housing assembly by spinning the blower wheel within the HVAC housings at the selected speed by use of the blower motor resistor.

The HVAC housing must be removed from the vehicle and disassembled for service of the heater core, A/C evaporator, blend-air and mode-air doors. The air inlet housing must be removed from HVAC housing for service of the recirculation door actuator and the recirculation-air door.

The blower motor is used to control the velocity of air moving through the HVAC housing by spinning the blower wheel within the housing at the selected speed whenever the ignition switch is in the On position and the blower control switch is in any position except Off.

Blower motor speed is controlled by regulating the path to ground through the blower motor control switch and the blower motor resistor. The blower motor receives battery current whenever the blower motor relay is energized. The blower motor relay output circuit is protected by a fuse in the integrated power module (IPM) located in the engine compartment.

The blower motor and blower motor wheel are factory balanced and cannot be adjusted or repaired. If faulty or damaged, the blower motor and blower wheel must be replaced as an assembly.

Possible causes of an inoperative blower motor include

1. Faulty fuse
2. Faulty blower motor resistor
3. Faulty blower motor switch
4. Faulty blower motor relay
5. Faulty blower motor
6. Faulty mode control switch
7. Faulty blower motor circuit wiring or wire harness connectors

The A/C refrigerant lines and hoses are used to carry the refrigerant between the various A/C system components. The refrigerant lines and hoses for the R-134a system on this vehicle consist of a barrier-hose design with a nylon tube sandwiched between rubber layers. The nylon tube helps to contain the R-134a refrigerant, which has a smaller molecular structure than R-12 refrigerant. The ends of the refrigerant lines are made from lightweight aluminum or steel, and commonly use braze-less fittings.

Any kinks or sharp bends in the refrigerant lines and hoses will reduce the capacity of the entire A/C system and can reduce the flow of refrigerant in the system. The radius of all bends in the flexible hose refrigerant lines should be at least ten times the diameter of the hose and the refrigerant lines should be routed so they are at least 80 millimeters (3 inches) away from the exhaust manifold(s) and exhaust pipe(s).

High pressures are produced in the refrigerant system when the A/C compressor is operating. Extreme care must be exercised to make sure that each of the refrigerant system connections is pressure-tight and leak free. It is a good practice to inspect all flexible hose refrigerant lines at least once a year to make sure they are in good condition and properly routed.

The refrigerant lines and hoses are coupled to other A/C system components with block-type and quick-connect type fittings. Flat gaskets and O-rings are used to mate the refrigerant line fittings with A/C system components to ensure the integrity of the refrigerant system.

The refrigerant lines and hoses cannot be repaired and, if faulty or damaged, they must be replaced.

When air passes through the fins of the A/C condenser, the high-pressure refrigerant gas within the A/C condenser gives up its heat. The refrigerant then condenses as it leaves the A/C condenser and becomes a high-pressure liquid. The volume of air flowing over the condenser fins is critical to the proper cooling performance of the A/C system. Therefore, it is important that there are no objects placed in front of the radiator grille openings at the front of the vehicle or foreign material on the condenser fins that might obstruct proper air flow. Also, any factory-installed air seals or shrouds must be properly reinstalled following radiator or A/C condenser service.

The A/C condenser cannot be repaired and, if faulty or damaged, it must be replaced.

Engine coolant is circulated through the heater hoses to the heater core at all times. As the coolant flows through the heater core, heat is removed from the engine and is transferred to the heater core fins and tubes. Air directed through the heater core picks up the heat from the heater core fins. The blend-air door allows control of the heater output air temperature by regulating the amount of air flowing through the heater core within the HVAC housing. The blower motor speed controls the volume of air flowing through the HVAC housing.

The heater core cannot be repaired and, if faulty or damaged, it must be replaced.

Two refrigerant system service ports are used to recover/recycle/evacuate/charge and test the A/C refrigerant system. Unique sizes are used on the service ports for the R-134a refrigerant system to ensure the system is not accidentally contaminated with R-12 refrigerant or service equipment used for R-12 refrigerant.

The high side service port is located on the A/C liquid line. The low side service port is located on the A/C accumulator. Both the high side and low side A/C service port valve cores are serviceable.

Each of the service ports has a threaded plastic protective cap installed over it from the factory. After servicing the refrigerant system, always reinstall both of the service port caps.

Spring-lock type refrigerant line couplers are used to connect the A/C accumulator and the A/C liquid line to the A/C evaporator. Secondary retaining clips are installed over the connected couplers for added protection.

The spring-lock refrigerant line couplers require A/C Line Disconnect Tools 7193 for disengaging the two coupler halves.

Scheme 3

The spring-lock type refrigerant line coupler is held together by a garter spring (6) inside a circular cage (7) on the male half of the fitting (1). When the two coupler halves are connected, the flared end of the female fitting (2) slips behind the garter spring inside the cage on the male fitting. The garter spring and cage prevent the flared end of the female fitting from pulling out of the cage. Some applications use a connection indicator ring (4) to help indicate when the two coupler halves are fully connected.

Two O-rings (8) are used to seal the coupler connections. These O-rings are compatible with R-134a refrigerant and must be replaced with O-rings made of the same material.

A secondary retaining clip (3) is installed over the connected coupler (5) for added protection.

Refrigerant enters the A/C evaporator through the A/C orifice tube as a low-temperature, low-pressure mixture of liquid and gas. As air flows over the fins of the A/C evaporator, the humidity in the air condenses on the fins, and the heat from the air is absorbed by the refrigerant. Heat absorption causes the refrigerant to boil and vaporize. The refrigerant becomes a low-pressure gas when it leaves the A/C evaporator.

The A/C evaporator cannot be repaired and, if faulty or damaged, it must be replaced.

The A/C discharge line is the refrigerant line that carries refrigerant from the A/C compressor to the A/C condenser.

The A/C discharge line has no serviceable parts except for the rubber O-ring seals and gaskets. The O-ring seals used on the connections are made from a special type of rubber not affected by R-134a refrigerant. The O-ring seals and gaskets must be replaced whenever the A/C discharge line is removed and installed.

If the A/C discharge line is found to be leaking or is damaged, it must be replaced.

The A/C liquid line is the refrigerant line that carries refrigerant from the A/C condenser to the A/C evaporator. The A/C liquid line uses a spring-lock type refrigerant line coupler to connect it to the A/C evaporator (Refer to HEATING & AIR CONDITIONING/PLUMBING/REFRIGERANT LINE COUPLER - DESCRIPTION) . The A/C liquid line is made from light-weight aluminum and uses braze-less fittings.

The A/C liquid line includes the high-side service port, the fixed A/C orifice tube and a fitting for the A/C pressure transducer. For more information refer to DESCRIPTION , DESCRIPTION and DESCRIPTION .

The A/C liquid line has no serviceable parts except for the rubber O-ring seals and gasket, high-side service port valve, cap and secondary retaining clip. The O-ring seals used on the connections are made from a special type of rubber not affected by R-134a refrigerant. The O-ring seals and gasket must be replaced whenever the A/C liquid line is removed and installed.

If the A/C liquid line is found to be leaking or is damaged, it must be replaced.

The A/C suction line is the refrigerant line that carries refrigerant from the A/C accumulator to the A/C compressor.

The A/C suction line has no serviceable parts except for the rubber O-ring seals and gaskets. The O-ring seals used on the connections are made from a special type of rubber not affected by R-134a refrigerant. The O-ring seals and gaskets must be replaced whenever the A/C suction line is removed and installed.

If the A/C suction line is found to be leaking or is damaged, it must be replaced.

The refrigerant oil used in R-134a refrigerant systems is a synthetic-based, Polyalkylene glycol (PAG), wax-free lubricant. Mineral-based R-12 refrigerant oils are not compatible with PAG oils, and should never be introduced to an R-134a refrigerant system.

There are different PAG oils available, and each contains a different additive package. The Denso 10S17 A/C compressor used in this vehicle is designed to use ND-8 PAG refrigerant oil. Use only this type of refrigerant oil in the refrigerant system.

After performing any refrigerant recovery or recycling operation, always replenish the refrigerant system with the same amount of the recommended refrigerant oil as was removed. Too little refrigerant oil can cause A/C compressor damage, and too much can reduce A/C system performance.

PAG refrigerant oil is more hygroscopic than mineral oil, and will absorb any moisture it comes into contact with, even moisture in the air. The PAG oil container should always be kept tightly capped until it is ready to be used. After use, recap the oil container immediately to prevent moisture contamination.

The refrigerant used in this air conditioning system is a HydroFluoroCarbon (HFC), type R-134a. Unlike R-12, which is a ChloroFluoroCarbon (CFC), R-134a refrigerant does not contain ozone-depleting chlorine. R-134a refrigerant is a non-toxic, non-flammable, clear, and colorless liquefied gas.

Even though R-134a does not contain chlorine, it must be reclaimed and recycled just like CFC-type refrigerants. This is because R-134a is a greenhouse gas and can contribute to global warming.

R-134a refrigerant is not compatible with R-12 refrigerant in an A/C system. Even a small amount of R-12 refrigerant added to an R-134a refrigerant system will cause A/C compressor failure, refrigerant oil sludge or poor A/C system performance. In addition, the Polyalkylene glycol (PAG) synthetic refrigerant oils used in an R-134a refrigerant system are not compatible with the mineral-based refrigerant oils used in an R-12 refrigerant system.

R-134a refrigerant system service ports, service tool couplers and refrigerant dispensing bottles have all been designed with unique fittings to ensure that an R-134a refrigerant system is not accidentally contaminated with the wrong refrigerant (R-12). There are also labels posted in the engine compartment of the vehicle and on the A/C compressor to identify that the A/C system is equipped with R-134a refrigerant.

Scheme 4

The fixed A/C orifice tube is installed in the A/C liquid line and provides a restriction in the liquid refrigerant line between the A/C condenser and the A/C evaporator. This restriction established the pressure differential between the high and low-pressure sides of the A/C system. The A/C orifice tube includes a diffuser screen (1), O-ring seals (2) to seal it to the inner wall of the A/C liquid line, an inlet filter screen (3) and the fixed orifice (4).

The fixed A/C orifice tube is used to meter the flow of liquid refrigerant into the A/C evaporator. The high-pressure liquid refrigerant from the A/C condenser expands into a low-pressure liquid as it passes through the metering orifice and diffuser screen of the A/C orifice tube.

The A/C orifice tube is not serviceable. The A/C orifice tube cannot be repaired and, if faulty or plugged, it must be replaced as part of the A/C liquid line.