Part 3 of 4

Fig.1 TRS90 Compressor:

A/C COMPRESSOR
The TRS9O is a fixed displacement type compressor. The compressor uses an integral thermal limiter switch to protect it from overheating. A high pressure relief valve located on the rear of the compressor housing is designed to protect the system from excessive pressure. The system uses polyalkylene glycol synthetic wax-free refrigerant oil SP-15 PAG.

The compressor is driven by the engine through an electric clutch, drive pulley and belt. The compressor is lubricated by refrigerant oil that is circulated throughout the system with the refrigerant. The compressor draws in low-pressure refrigerant vapor from the evaporator through its suction port. It then compresses the refrigerant into a high-pressure, high-temperature refrigerant vapor, which is then pumped to the condenser through the compressor discharge port.

A high pressure relief valve is located on the rear surface of the compressor housing. The high pressure relief valve vents the system when a discharge pressure of 3445 - 4135 kPa (500 - 600 psi) or above is reached. The valve closes with a minimum discharge pressure of 2756 kPa (400 psi) is reached. This prevents damage to the compressor and other system components. The compressor and relief valve cannot be repaired and must be replaced if damaged.

A/C CONDENSER
The condenser is a heat exchanger that allows the high-pressure refrigerant gas being discharged by the compressor to give up its heat to the air passing over the condenser fins. The condenser is located in front of the vehicles radiator.

When air passes through the condenser fins the refrigerant gives up its heat. The refrigerant then condenses as it leaves the condenser and becomes a high-pressure liquid. The volume of air flowing over the condenser fins is critical for proper air conditioning performance. It is important that there are no objects placed in front of the radiator grille openings or foreign material on the condenser fins that might obstruct proper air flow. The condenser cannot be repaired and if faulty or damaged must be replaced. All factory-installed air seals or shrouds must he installed following service to maintain proper air flow.

Fig.4 Expansion Valve:

A/C EXPANSION VALVE
The "H" valve-type Thermal Expansion Valve (TXV) is located in front of the heater-A/C housing between the liquid and suction lines and the evaporator coil.

The expansion valve is a calibrated unit and cannot be adjusted or repaired. If faulty or damaged, the expansion valve must be replaced.

High pressure high temperature liquid refrigerant from the liquid line passes through the expansion valve orifice. The refrigerant is converted into a low-pressure, low-temperature mixture of liquid and gas before it enters the evaporator coil. A temperature sensor in the expansion valve control head monitors refrigerant temperature leaving the evaporator coil through the suction line. The valve adjusts the orifice size at the liquid line to let the proper amount of refrigerant into the evaporator coil. Controlling refrigerant flow through the evaporator ensures that none of the refrigerant leaving the evaporator is in a liquid state, which could damage the compressor.

Fig.6 Evaporator Coil:

A/C EVAPORATOR
The evaporator coil is located in the heater-A/C housing on the passenger side of the vehicle. The evaporator coil is positioned in the housing so all the air entering the housing passes over the evaporator fins then through the system ducts and outlets. Air passing over the evaporator fins will only be conditioned when the A/C system is ON. The evaporator coil cannot be repaired and must be replaced if faulty or damaged.

Refrigerant enters the evaporator from the expansion valve as a low-temperature low-pressure mixture of liquid and gas. As air flows over the evaporator fins, humidity in the air condenses on the fins and 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 before it leaves the evaporator.

DISCHARGE LINE
The discharge line is made from reinforced rubber with a nylon liner on the inner walls. The line has a light weight aluminum fittings at the compressor and condenser end. The O-rings used to seal the connections are made from a special type of rubber not affected by R-134a refrigerant. O-rings must replaced whenever the line is removed and installed.

CAUTION: Use only O-rings specified for the vehicle. Failure to use correct O-ring will cause the connection to leak.

SUCTION LINE
The suction line is made from reinforced rubber with a nylon liner on the inner walls. The line has a light weight aluminum fitting at the compressor end and a quick connect fitting at the expansion valve end. The quick connect has two O-rings to seal the connection made from a special type of rubber not affected by R-134a refrigerant. The O-rings must be replaced whenever the line is removed and installed.

CAUTION: Use only O-rings specified for the vehicle. Failure to use correct O-ring will cause the connection to leak.

RECEIVER / DRIER
The receiver/drier is mounted on the right side of the engine compartment. It is part of the liquid line, between the condenser outlet and evaporator inlet.

High-pressure liquid refrigerant from the condenser flows into the receiver/drier. The receiver/drier filters the refrigerant to prevent foreign material from contaminating the expansion valve. A desiccant bag inside absorbs any moisture which may have become trapped in refrigerant system. In periods of high demand air conditioner operation, it acts as a reservoir to store surplus refrigerant. If the receiver/drier is faulty, damaged, contaminated or the system has been left open to the atmosphere for an undetermined period, it must be replaced.