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.
VDOT Air Conditioning System
The Variable Displacement Orifice Tube (VDOT) air conditioning system employs a V 5 compressor that can match the automotive air conditioning demand under all conditions without cycling. The basic compressor mechanism is a variable angle wobble-plate with axially oriented cylinders. The control of the compressor displacement is a bellows actuated control valve located in the rear head of the compressor that senses suction pressure. The wobble-plate angle and compressor displacement are controlled by the crankcase-suction pressure differential. When the A/C capacity demand is high, the suction pressure will be above the control point; the valve will maintain a bleed from the crankcase to suction; no crankcase-suction pressure differential; and the compressor will have maximum displacement. When the A/C capacity-demand is lower and the suction pressure reaches the control point, the valve will bleed discharge gas into the crankcase and close off a passage from the crankcase to the suction plenum. The angle of the wobble-plate is controlled by a force balance on the five pistons. A slight elevation of the crankcase-suction pressure differential creates a total force on the pistons resulting in a movement about the wobble-plate pivot pin that reduces the plate angle.
The compressor has a unique lubrication system. The crankcase-suction bleed is routed through the rotating wobble-plate for lubrication of the wobble-plate bearing. The rotation act as an oil separator, which removes some of the oil from the crankcase-suction bleed, rerouting it to the crankcase where it can lubricate the compressor mechanism.
The compressor, depending upon engine usage, is cut-off under certain conditions such as wide-open throttle, low idle speed, low air temperature and high power steering loads. The V5 compressor has a mechanical destroker that will begin to destroke during engine speeds of 3,000-3,800 RPM.
When the engine is turned "OFF" with the A/C system operating, the refrigerant in the system will flow from the high pressure side of the evaporator tube orifice to the low pressure side until the pressure is equalized. This may be detected as a faint sound of liquid flowing (hissing) for 30 to 60 seconds and is a normal condition.
Air Conditioning Accumulator
The accumulator is located on the right side wheelhouse panel, just downstream from the evaporator. It functions as a moisture separator that receives refrigerant liquid and refrigerant oil from the evaporator.
At the bottom of the accumulator is the desiccant, which acts as a drying agent for moisture that may have entered the system.
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 Evaporator Tube Orifice
The plastic tube, with its mesh screen and orifice, is located just forward of the evaporator fitting between the condenser outlet and evaporator inlet. It provides a restriction to the high-pressure liquid refrigerant in the liquid line, metering the flow of refrigerant to the evaporator as a vapor. The evaporator tube orifice is protected from contamination by filter screens on both inlet and outlet sides.
When system diagnostics indicate a restricted evaporator tube orifice, it may not be necessary to replace the tube. Metal chips, flakes or slivers found on the screen may be removed with compressed air and the evaporator tube orifice may be reused if:
^ The plastic frame is not broken.
^ The brass expansion tube is not damaged or plugged.
^ The screen material is not torn.
^ The screen is not plugged with fine gritty material.
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 ACCUMULATOR, AIR CONDITIONING
6 EVAPORATOR, AIR CONDITIONING
7 HOSE, AIR CONDITIONING COMPRESSOR AND CONDENSER
8 HOSE, ACCUMULATOR
9 TUBE, AIR CONDITIONING EVAPORATOR
10 BRACKET, AIR CONDITIONING ACCUMULATOR
11 BOLT/SCREW, AIR CONDITIONING ACCUMULATOR CLAMP
12 BOLT/SCREW, AIR CONDITIONING ACCUMULATOR BRACKET
13 O-RING, AIR CONDITIONING EVAPORATOR TUBE
14 O-RING, AIR CONDITIONING COMPRESSOR AND CONDENSER HOSE
16 O-RING, AIR CONDITIONING ACCUMULATOR HOSE
17 O-RING, AIR CONDITIONING COMPRESSOR AND CONDENSER HOSE
18 SEAL, AIR CONDITIONING COMPRESSOR AND CONDENSER HOSE
20 O-RING, AIR CONDITIONING REFRIGERANT PRESSURE SENSOR
21 VALVE, AIR CONDITIONING REFRIGERANT PRESSURE SENSOR
22 SENSOR, AIR CONDITIONING REFRIGERANT PRESSURE SENSOR
23 CORE, AIR CONDITIONING REFRIGERANT SERVICE VALVE
26 CAP, AIR CONDITIONING REFRIGERANT CHARGE VALVE
27 BOLT/SCREW, AIR CONDITIONING EVAPORATOR TUBE
28 BOLT/SCREW, AIR CONDITIONING COMPRESSOR AND CONDENSER HOSE
33 RETAINER, RADIATOR AIR UPPER BAFFLE
38 BOLT/SCREW, AIR CONDITIONING COMPRESSOR
39 NUT, AIR CONDITIONING COMPRESSOR