A/C Cycle With Auxiliary

The auxiliary A/C system operates from the vehicles primary A/C system. The front A/C system must be on to allow the auxiliary A/C system to function.

Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automobile use. R-134a is a very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.

The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system.

Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.

The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line. The liquid line flow is split and the liquid refrigerant flows to both the front A/C system and to the liquid line for the auxiliary A/C system. The liquid refrigerant, flowing to the auxiliary A/C system, flows into the rear TXV.

The rear TXV is located at the rear evaporator inlet. The TXV is the dividing point for the high and low pressure sides of the auxiliary A/C system. As the refrigerant passes through the TXV, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to vaporize at the TXV. The TXV also meters the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the TXV flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the auxiliary HVAC module and passes through the evaporator core. Warm, moist air will cause the liquid refrigerant to boil inside of the evaporator core. The boiling refrigerant absorbs the moisture and heat from the ambient air. The refrigerant exits the evaporator through the suction line and back to the front A/C systems suction line. Refrigerant in the front A/C system suction line flows back to the compressor, in a vapor state, and completes the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

The conditioned air is distributed through the auxiliary HVAC module for passenger comfort. The heat and moisture removed from the rear passenger compartment will also change form, or condense, and is discharged from the auxiliary HVAC module as water.