Evaporator coil. Expansion valve

Evaporator coil

FRONT

DESCRIPTION

The evaporator coil is located in the heater-A/C housing, under the instrument panel. The evaporator coil is positioned in the heater-A/C housing so that all air that enters the housing must pass over the fins of the evaporator before it is distributed through the system ducts and outlets. However, air passing over the evaporator coil fins will only be conditioned when the compressor is engaged and circulating refrigerant through the evaporator coil tubes.

OPERATION

Refrigerant enters the evaporator from the expansion valve as a low-temperature, low-pressure mixture of liquid and gas. As air flows over the fins of the 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 lowpressure gas when it leaves the evaporator.

The evaporator coil cannot be repaired and, if faulty or damaged, it must be replaced.

REAR

DESCRIPTION

The rear evaporator coil is located in the rear overhead A/C unit housing, above the headliner. The evaporator coil is positioned in the overhead A/C unit housing so that all air that enters the housing must pass over the fins of the evaporator before it is distributed through the system outlets. However, air passing over the evaporator coil fins will only be conditioned when the compressor is engaged and circulating refrigerant through the evaporator coil tubes.

OPERATION

Refrigerant enters the evaporator from the rear expansion valve as a low-temperature, low-pressure mixture of liquid and gas. As air flows over the fins of the 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 evaporator.

The rear evaporator coil cannot be repaired and, if faulty or damaged, the rear evaporator coil must be replaced.

Expansion valve

FRONT

DESCRIPTION

The front "H" valve-type thermal expansion valve (TXV) is located at the dash panel between the liquid and suction lines, and the evaporator coil. High-pressure, high temperature liquid refrigerant from the liquid line passes through the expansion valve orifice, converting it into a low-pressure, low-temperature mixture of liquid and gas before it enters the evaporator coil.

OPERATION

A sensor in the expansion valve control head monitors the temperature and pressure of the refrigerant leaving the evaporator coil through the suction line, and adjusts the orifice size at the liquid line to let the proper amount of refrigerant into the evaporator coil to meet the vehicle cooling requirements. Controlling the refrigerant flow through the evaporator ensures that none of the refrigerant leaving the evaporator is still in a liquid state, which could damage the compressor.

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

REAR

DESCRIPTION

Vehicles equipped with the optional rear overhead A/C unit have an H-type thermal expansion valve (TXV) located underneath the passenger side of the vehicle floor panel, next to the sill. It performs the same function as the front expansion valve, to monitor refrigerant temperature and pressure at the control head and meter the refrigerant entering the evaporator to meet the vehicle cooling requirements.

OPERATION

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