Refrigeration System
A/C AmplifierThe A/C amplifier controls the operation of the compressor clutch in response to signals received from the A/C dual pressure switch, the evaporator temperature sensor, and the Powertrain Control Module (PCM).
With the air conditioning system in operation, the A/C amplifier performs the following functions:
^ Energizes the compressor clutch in response to air conditioning system request and upon determination of favorable system conditions for air conditioning operation.
^ De-energizes the compressor clutch in response to a high refrigerant pressure signal (from the dual pressure switch), a low refrigerant pressure signal (from the A/C dual pressure switch), a low evaporator temperature signal (from the evaporator temperature sensor), or a high engine demand signal (from the PCM).
Compressor
The compressor is driven by a drive belt from the engine crankshaft through the compressor clutch pulley. The compressor pulley rotates freely, without turning the compressor shaft, until an electromagnetic clutch coil is energized. When voltage is applied 10 energize the clutch coil, a clutch plate and hub assembly is drawn rearward toward the pulley. The magnetic field locks the clutch plate and pulley together as one unit to drive the compressor shaft.
As the compressor shaft turns, the compressor performs two main functions: it compresses the low-pressure refrigerant vapor from the evaporator into a high-pressure, high-temperature vapor. The compressor also pumps refrigerant (and refrigerant oil) throughout the air conditioning system.
For compressor service procedures, refer to Air Conditioning Compressor Service.
Condenser
Figure 1 - Air Conditioning System System Components:
The condenser assembly is mounted in front of the radiator and is comprised of small coils and cooling fins (Figure 1). When the high-pressure, high-temperature vapor, just discharged from the compressor, enters the condenser, heat is transferred from the refrigerant to passing ambient air through the condenser's cooling fins. By the time the refrigerant has traveled the length of the condenser's coils, most of the vapor has cooled and condensed into a liquid. Refrigerant passing through the condenser is transformed from a high-pressure, high-temperature vapor into a high-pressure, medium-temperature liquid.
Condenser Fan
The condenser fan is crucial to the proper operation of the air conditioning system. The fan ensures a sufficient amount of airflow across the condenser throughout the vehicle's operating range. The fan should be checked during all air conditioning diagnosis procedures. Special attention should be given to the fan whenever excessive high-side pressure is encountered.
Evaporator
The evaporator is housed in the evaporator case, located behind the right-hand side of the instrument panel. During air conditioning operation, ambient air is directed through the fins of the evaporator and into the vehicle's passenger compartment. Heat from the ambient air is transferred to the low-pressure, low-temperature liquid refrigerant passing through the evaporator.
Expansion Valve
The expansion valve regulates the flow of liquid refrigerant into the core of the evaporator. As the condensed liquid refrigerant is released through the expansion valve, the refrigerant's pressure decreases considerably. As the pressure drops, the refrigerant's temperature also drops. Refrigerant passing through the expansion valve is transformed from a high-pressure, medium-temperature liquid into a low-pressure, low-temperature liquid.
Receiver/Dryer
Receiver/Dryer (Sectional View):
The receiver/dryer is mounted to the front of the condenser and is connected to the condenser outlet pipe between the condenser and the evaporator.
In order for the air conditioning system to operate properly, the receiver/dryer must perform three functions: First, the receiver/dryer serves as a temporary storage container for condensed liquid refrigerant; second, the receiver/dryer acts as a filter which removes moisture and contaminants from the system; third, the receiver/dryer incorporates a sight glass, through which the state of the system's refrigerant can be determined.
Refrigerant-134a
CAUTION: Avoid breathing A/C Refrigerant-134a and lubricant vapor or mist. Exposure may irritate eyes, nose and throat. To remove R-134a from the A/C system, use service equipment certified to meet the requirements of SAE J2210 (R-134a recycling equipment). If accidental system discharge occurs, ventilate work area before resuming service. Additional health and safety information may be obtained from refrigerant and lubricant manufacturers.
Like the coolant in the engine cooling system, the refrigerant is the substance in the air conditioning system that absorbs, carries and then releases heat. Although various substances are used as refrigerants in other types of refrigeration systems, past automotive air conditioning systems used a type called Refrigerant-12 (R-12).
This vehicle uses a new type of refrigerant called Refrigerant-134a (R-134a). It is a non-toxic, non-flammable, clear colorless liquefied gas.
While the R-134a A/C system is very similar to an R-12 A/C system, the differences in the refrigerant, lubricants and service equipment are important.
Notice:R-134a refrigerant is not compatible with R-12 refrigerant in an air conditioning system. R-12 in an R-134a system will cause compressor failure, refrigerant oil sludge or poor air conditioning system performance.
Notice:Refrigerant-134a carries a charge of special lubricating oil, polyalkaline glycol (PAG) refrigerant oil. GM PAG refrigerant oil will have a slight blue tint. The oil is hydroscopic (absorbs water from the atmosphere) and should be stored in closed containers.