Captiva

Air Temperature Description and Operation

The SP-17 is a fixed 173 cc displacement swash plate compressor. It consists of five double-ended pistons reciprocated in 10 cylinder bores by the swash plate and shaft assembly. There are 10 hemispheric shoes connecting the pistons to the swash plate and shaft assembly. As the swash plate rotates, the shoes swivel. Thus the rotary motion of the swash plate is converted to the reciprocating motion of the pistons.

All compressors are belt-driven from the engine crankshaft through the compressor clutch pulley. The compressor pulley rotates without driving the compressor shaft until an electromagnetic clutch coil is energised. When voltage is applied to energise the clutch coil, the clutch plate and hub assembly is drawn rearward toward the pulley. The magnetic force locks the clutch plate and pulley together as one unit to drive the compressor shaft.

As the compressor shaft is driven, it compresses the low- pressure refrigerant vapour from the evaporator into a high-pressure, high-temperature vapour. The refrigerant oil which is used to lubricate the compressor is carried with the refrigerant.

The compressor is equipped with a pressure relief valve which is placed in the system as a safety factor. Under certain conditions, the refrigerant on the discharge side may exceed the designed operating pressure. In order to prevent system damage, the valve is designed to open automatically at approximately 3 171 to 4 137 kPa (460 to 600 psi) in an R-134a system. Conditions that might cause this valve to open, such as a defective pressure transducer, an inoperative cooling fan, etc., should be corrected. The refrigerant oil and the refrigerant should be replaced as necessary.

The condenser assembly in front of the radiator consists of coils which carry the refrigerant, and cooling fins that provide the rapid transfer of heat. The air passing through the condenser cools the high-pressure refrigerant vapour and causes it to condense into a liquid.

The expansion valve can fail in three different positions: open, closed, or restricted.

An expansion valve that fails in the open position will result in a noisy A/C compressor or no cooling. The cause can be a broken spring, a broken ball, or excessive moisture in the A/C system. If the spring or the ball are found to be defective, replace the expansion valve. If excessive moisture is found in the A/C system, recycle the refrigerant.

An expansion valve that fails in the closed position will result in low suction pressure and no cooling. This may be caused by a failed power dome or excessive moisture in the A/C system. If the power dome on the expansion valve is found to be defective, replace the expansion valve. If excessive moisture is found in the A/C system, recycle the refrigerant.

A restricted expansion valve will result in low suction pressure and no cooling. This may be caused by debris in the refrigerant system. If debris are believed to be the cause, recycle the refrigerant, replace the expansion valve, and replace the receiver-dryer.

The evaporator is a device which cools and dehumidifies the air before it enters the vehicle. High-pressure liquid refrigerant flows through the expansion tube orifice and becomes a low-pressure gas in the evaporator. The heat in the air passing through the evaporator core is transferred to the cooler surface of the core, which cools the air. As the process of heat transfer from the air to the evaporator core surface is taking place, any moisture or humidity in the air condenses on the outside surface of the evaporator core and is drained off as water.

The sealed receiver-dryer assembly is connected to the condenser outlet pipe. It acts as a refrigerant storing container, receiving liquid, vapour, and refrigerant oil to the evaporator.

At the bottom of the receiver-dryer is the desiccant, which acts as a drying agent for the moisture that may have entered the system.

The heater core heats the air before it enters the vehicle. Engine coolant is circulated through the core to heat the outside air passing over the fins of the core. The core is functional at all times and may be used to temper conditioned air in the A/C mode as well as in the heat or the vent modes.

Pressure transducer switching incorporates the functions of the high-pressure and the low-pressure cut-out switches along with the fan cycling switch. The pressure transducer is located in the high-side liquid refrigerant line behind the right headlamp, between the right front inner wing and the air filter assembly. The output from this pressure transducer goes to the engine control module (ECM) which controls the compressor function based on the pressure signal.

During full throttle acceleration, the throttle position sensor (TPS) sends a signal to the engine control module (ECM), which then controls the compressor clutch.