Refrigeration System

CCOT System:

Accumulator
The sealed accumulator assembly connects to the evaporator outlet pipe. It functions as a liquid/vapor separator that receives refrigerant vapor, some liquid refrigerant and refrigerant oil from the evaporator. It only allows refrigerant vapor and oil to flow to the compressor.

At the bottom of the accumulator is desiccant that acts as a drying agent for moisture that may have entered the system. An oil bleed hole is also located near the bottom of the accumulator outlet pipe to provide an oil return path to the compressor.

A low-side pressure service fitting is located on the accumulator. A similar service fitting is provided for mounting the cycling pressure switch. It is not necessary to discharge the system to replace the switch. The accumulator is serviced only as a replacement assembly.


Compressor
The Harrison HT-6 compressor is belt driven by 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 assembly are drawn rearward toward the pulley. The magnetic force locks the clutch plate and pulley together as one unit to drive the compressor shaft.

All replacement compressors from service parts will have 240 ml (8 fl oz) of oil in the crankcase When replacing compressors, drain the oil from the old compressor into an approved container, and note the amount drained. You must also drain the oil from the new compressor, then fill the new compressor with new oil in the same amount that was drained from the old compressor.

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

Expansion (Orifice) Tube
The plastic expansion tube, with its mesh screen and orifice is located in the condenser outlet pipe in all models except Suburbans with rear air conditioning (RPO C69). Suburbans equipped with rear air conditioning use a Y-shaped junction block in the tube between the condenser and the front evaporator. The junction block is located near the right side of the radiator support. The expansion tube is located between the junction block and the front evaporator. Refer to A/C Hose/Line for more information and component locator views.

The orifice tube provides a restriction to the high-pressure liquid refrigerant in the liquid line, metering the flow of refrigerant to the evaporator as a low-pressure liquid. The expansion tube and orifice are protected from contamination by filter screens on both inlet and outlet sides. The tube is serviced only as a replacement assembly.

When the engine is turned "OFF" with the air conditioning operating, the refrigerant in the system will flow from the high-pressure side of the expansion 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.

When system diagnostics indicate a restricted expansion tube, it may not be necessary to replace it. Metal chips, flakes, or slivers found on the screen may be removed with compressed air. The expansion tube may be reused if:

- The plastic frame is not broken.
- The expansion tube is not damaged or plugged.
- The screen material is not torn.
- The screen is not plugged with fine gritty material.

Thermo Expansion Valve (TXV)
The rear air conditioning system uses a Thermo Expansion Valve (TXV). The valve consists of the capillary tube, body, actuating pins, seat and orifice. At the high pressure liquid inlet, a fine mesh screen prevents dirt, filings or other foreign material from entering the valve orifice.

When the valve is connected in the system, high pressure liquid refrigerant enters the valve through the screen from the condenser and passes on to the seat and orifice where it changes into a low pressure liquid.

The low pressure liquid leaves the valve and flows into the evaporator core where it absorbs heat from the evaporator core and changes to a low pressure vapor and leaves the evaporator core. The capillary tube is clamped to the low pressure vapor line just below the outlet of the evaporator. The capillary tube is held in contact with the rear evaporator outlet tube by a metal clip placed near the end of the tube.

Evaporator
The evaporator cools and dehumidifies the air before it enters the vehicle. High pressure liquid refrigerant flows through the orifice tube into the low-pressure area of 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 surface of the evaporator core and is drained off as water.

Heater Core
In any air conditioning mode, the heater core heats the cool, dehumidified air to achieve the desired temperature. The position of the control assembly temperature rotary knob determines how much heat is added to the incoming air.

High Pressure Relief Valve
The compressor is equipped with a pressure relief valve as a safety factor. Under certain conditions, the refrigerant on the discharge side may exceed the designed operating pressure. Exceeding this pressure limit may cause refrigerant loss out of the pressure relief valve. To prevent refrigerant loss or compressor damage, the high pressure cut-off switch opens automatically at approximately 3036 kPa (440 psi). When the switch opens, current to the compressor clutch is interrupted. Any condition that causes the switch to open will keep the compressor from operating.

Refrigerant-134a
This vehicle uses Refrigerant-134a (R-134a). It is a non-toxic, non-flammable, clear, colorless liquefied gas.

CAUTION: Avoid breathing A/C Refrigerant-134a and lubricant vapor and 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 the work area before resuming service. Additional health and safety information may be obtained from the 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, some automotive air conditioning systems use a type called Refrigerant-12 (R-12).


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 lubricant called polyalkaline glycol (PAG) refrigerant oil. GM (PAG) refrigerant oil has a slight blue tint. The oil is hydroscopic (absorbs water from the atmosphere). Store it in closed containers.