Refrigeration System
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 a R-134a system will cause compressor failure, refrigerant oil sludge or poor air conditioning system performance.
Refrigerant 134a carries a charge of a special lubricating oil, polyalkylene 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 he stored in closed containers.
Use only polyalkylene glycol (PAG) synthetic refrigerant oil for internal circulation through the R-134a A/C system and only mineral base 525 viscosity refrigerant oil on fittings threads and O-rings. If lubricants other than those specified are used, compressor failure and/or fitting seizure is likely to occur.
TXV Air Conditioning System
The Thermostatic Expansion Valve (TXV) refrigerant system, on 5.7L VIN P equipped vehicles, is designed to cycle the compressor on and off to maintain desired cooling and to prevent evaporator freeze. Passenger compartment comfort is maintained by the temperature lever on the control.
Control of the refrigeration cycle (on and off operation of the compressor is done with the evaporator temperature sensor The evaporator temperature sensor is a freeze protection device for the evaporator. When the air conditioning mode (max, norm, bi-level, defrost) is selected, voltage is supplied to the compressor clutch coil. When evaporator temperature approaches the freezing point (the low setting of the switch), the switch opens the compressor clutch circuit and disengages the clutch. The compressor remains disengaged until the temperature rises above a preset temperature. As the temperature rises and reaches a preset point, the switch closes, re-energizing the clutch coil. This cycling continues and attempts to maintain evaporator temperature at 1°C (33°F) with slight variation due to outside air temperature and humidity. Because of this cycling, some slight increases and decreases of engine speed/power may be noticed under certain conditions. This is normal as the system is designed to cycle to maintain desired cooling, thus preventing evaporator freeze-up. The thermostatic expansion valve (TXV) regulates the flow of liquid refrigerant into the evaporator. Its operation reduces the pressure and temperature of the refrigerant flowing to the evaporator.
The compressor, depending upon engine usage, is also cut off under certain other conditions such as wide-open throttle, low idle speed and low air temperature.
Air Conditioning Receiver and Dehydrator
The receiver and dehydrator is located on the right side wheelhouse panel, just downstream from the condenser. It functions as a moisture separator that receives refrigerant liquid and refrigerant oil from the condenser. It only allows refrigerant liquid and a small amount of oil to continue on to the thermostatic expansion valve.
At the bottom of the receiver and dehydrator is the desiccant, which acts as a drying agent for moisture that may have entered the system. A filter is also located near the bottom of the receiver and dehydrator outlet pipe to keep any particles from plugging the thermostatic expansion valve.
Air Conditioning Compressor
The air conditioning compressor is driven by a 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 to energize the clutch coil, a clutch plate and hub is drawn rearward toward the pulley. The magnetic force locks the clutch plate and pulley together as one unit to drive the compressor shaft.
Air Conditioning Condenser
The air conditioning condenser in front of the radiator is made up of coils, which carry the refrigerant and cooling fins to provide rapid transfer of heat. The air passing through the condenser cools the high-pressure refrigerant vapor, causing it to condense into a liquid.
Engine Electric Coolant Fans
Coolant fan operation is crucial to the proper operation of the air conditioning system. The coolant fans ensures the proper amount of air flow across the condenser throughout the vehicle operating range.
Fan operation should be checked during any air conditioning diagnosis procedure. Special attention should be given to the fan whenever excessive high side pressures are encountered.
Air Conditioning Thermostatic Expansion Valve
The purpose of the thermostatic expansion valve is to regulate the flow of refrigerant through the evaporator to optimize its cooling performance. This is accomplished by monitoring the refrigerant conditions at the evaporator outlet and adjusting the inlet flow accordingly. This assures that all the liquid is evaporated before it is returned to the compressor.
The refrigerant flow is controlled by the movement of a shaft that pushes a ball from its seat. As the ball is unseated, more flow is allowed through the evaporator.
Shaft movement is controlled by the power dome which has two separate sides. The thermal side of the power dome is sealed and charged with refrigerant. The system side of the power dome is exposed to the pressure of the evaporator outlet or low side. Refrigerant exiting the evaporator flows over part of the thermal side of the power dome. The sealed refrigerant in the thermal side responds to the temperature changes of the refrigerant flowing out of the evaporator. As the refrigerant temperature rises, the pressure of the thermal side increases.
If the pressure on the thermal side of the power dome is greater than the pressure on the system side (the evaporator outlet or low-side pressure), the shaft moves down and pushes the ball off the seat allowing more refrigerant flow through the evaporator. When the opposite is true, the shaft moves up and re-seats the ball reducing flow. A spring at the bottom of the thermostatic expansion valve is not adjustable.
Although the thermostatic expansion valve controls evaporator refrigerant flow, air conditioning capacity control (to prevent ice build-up) is managed by compressor cycling which is controlled by the powertrain control module (PCM).
Air Conditioning Evaporator
The evaporator is a device which cools and dehumidifies the air before it enters the vehicle. High-pressure refrigerant flows through the thermostatic expansion valve (5.7L VIN P) or the orifice tube (3800 VIN K) and becomes low-pressure refrigerant before entering the evaporator. The heat in the air passing through the evaporator core is lost to the cooler surface of the core, thereby cooling the air. As the process of heat loss from the air to the evaporator core surface is taking place, any moisture (humidity) in the air condenses on the outside of the evaporator core and is drained off as water.
Air Conditioning Compressor Pressure Relief Valve
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. To prevent system damage, the valve is designed to open automatically at approximately 3036 kpa (440 psi). Any condition that causes this valve to open should be corrected, and the refrigerant oil should be replaced as necessary. The air conditioning refrigerant pressure sensor should also be checked for proper calibration.
Image Legend
1 MODULE, HEATER AND AIR CONDITIONING EVAPORATOR
2 COMPRESSOR, AIR CONDITIONING
3 CONDENSER, AIR CONDITIONING
4 RECEIVER AND DEHYDRATOR, AIR CONDITIONING
5 EVAPORATOR, AIR CONDITIONING
6 VALVE, AIR CONDITIONING THERMOSTATIC EXPANSION
7 HOSE, AIR CONDITIONING COMPRESSOR AND CONDENSER
8 TUBE, AIR CONDITIONING RECEIVED DEHYDRATOR
9 TUBE, AIR CONDITIONING RECEIVER DEHYDRATOR
10 BRACKET, AIR CONDITIONING RECEIVER DEHYDRATOR
11 BOLT/SCREW, AIR CONDITIONING RECEIVER DEHYDRATOR CLAMP
12 BOLT/SCREW, AIR CONDITIONING RECEIVER DEHYDRATOR BRACKET
13 O-RING, AIR CONDITIONING RECEIVER DEHYDRATOR TUBE
14 O-RING, AIR CONDITIONING EVAPORATOR TUBE
15 SEAL, AIR CONDITIONING EVAPORATOR TUBE
16 SEAL, AIR CONDITIONING COMPRESSOR AND CONDENSER HOSE
17 O-RING, AIR CONDITIONING CONDENSER FITTING
18 SEAL, AIR CONDITIONING COMPRESSOR HOSE
20 O-RING, AIR CONDITIONING REFRIGERANT PRESSURE SENSOR
21 VALVE, AIR CONDITIONING REFRIGERANT PRESSURE SENSOR
22 SENSOR, AIR CONDITIONING REFRIGERANT PRESSURE
23 CORE, AIR CONDITIONING REFRIGERANT SERVICE VALVE
26 GAP, AIR CONDITIONING REFRIGERANT CHARGE VALVE
27 BOLT/SCREW, AIR CONDITIONING RECEIVER DEHYDRATOR TUBE
28 BOLT/SCREW, AIR CONDITIONING COMPRESSOR AND CONDENSER HOSE
29 BOLT/SCREW, AIR CONDITIONING THERMOSTATIC EXPANSION VALVE
30 BOLT/SCREW, AIR CONDITIONING COMPRESSOR AND CONDENSER HOSE CLIP BRACKET
32 BRACKET, AIR CONDITIONING COMPRESSOR HOSE CLIP
33 RETAINER, RADIATOR AIR UPPER BAFFLE
34 STRAP, AIR CONDITIONING COMPRESSOR AND CONDENSER HOSE
38 BOLT/SCREW, AIR CONDITIONING COMPRESSOR
42 GASKET, EVAPORATOR BLOCK