(CCOT) Refrigeration System

General Arrangement With Front Heat And A/C, And Rear Heat And A/C (C69):

General Arrangement With Front Heat And A/C, And Rear Heat And A/C (YF7):

General Arrangement With Front Heat And A/C (C60):

The Cycling Clutch Orifice Tube (CCOT) refrigerant system is designed to cycle the compressor on and off to maintain desired cooling and prevent evaporator freeze-up. Passenger compartment comfort is maintained by the temperature selector on the controller.

Control of the refrigeration cycle (on and off operation of the compressor) is done with a switch that senses low side pressure as an indicator of evaporator pressure. The cycling pressure switch is the freeze protection device in the system and senses refrigerant pressure on the suction side of the system. This switch is located on the accumulator. During air temperatures of 10°C (50°F), the equalized pressures within the charged air conditioning system close the contacts of the pressure switch.

When an air conditioning mode is selected, electrical energy is supplied to the compressor clutch coil. As the compressor reduces the evaporator pressure to approximately 159 kPa (23 psi), the pressure switch opens, de-energizing the compressor clutch. As the system equalizes and the pressure reaches approximately 315 kPa (46 psi), the pressure switch contacts close, re-energizing the clutch coil. This cycling continues and attempts to maintain evaporator discharge air temperature at approximately 1°C (33°F).

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 and prevent evaporator freeze-up.

Additional compressor protection results from the operating characteristics of the low-side cycling pressure system. If a massive discharge occurs in the low side of the system, or the orifice tube becomes plugged, low-side pressures could be insufficient to close the contacts of the pressure switch. In the event of a low charge, insufficient cooling accompanied by rapid compressor clutch cycling will be noticed at high air temperatures.

When the engine is turned "OFF" after the air conditioning system has been operating, the refrigerant in the system flows from the high-pressure side of the expansion (orifice) tube to the low-pressure side until the pressure is equalized. This may be detected as a hissing sound for 30 to 60 seconds and is a normal condition. This sound actually occurs during operation as well, but is not audible with the engine running.

The heating and air conditioning systems that are available for this vehicle are described below and in the illustrations.

^ C36 Rear Auxiliary Heat Only
^ C42 Front Base Heat
^ C60 Front Heat and A/C
^ C69 Rear Auxiliary A/C and Heat
^ C42 & C36 Front and Rear Heat
^ 060 & C36 Front Heat A/C and Rear Heat
^ 060 & C69 Front and Rear A/C and Heat

Accumulator

The sealed accumulator assembly is connected 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 continue on to the compressor.

At the bottom of the accumulator is the desiccant, which 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 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 DELPHI Thermal HT-6 compressor is belt driven 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 the clutch coil, a 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.

All replacement compressors from service parts will have 240 ml (8 ft. oz.) of oil in the crankcase, the oil must be drained and retained. Then replace the oil in the same amount as previously recorded from the old compressor.

Condenser

The condenser assembly in the front of the radiator is made up of tubes that carry 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.

Expansion Tube (Orifice)

The plastic expansion tube, with its mesh screen and orifice, is located in the evaporator inlet pipe. It 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 (orifice) is 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" after the air conditioning has been 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 and 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.
^ Undamaged "O" ring.

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 is a device that 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 mode, the heater core can be used to heat the air to achieve the desired temperature. The position of the control assembly temperature knob will determine how much heat will be added to the incoming air.

High Pressure Relief Valve

The compressor is equipped with a pressure relief valve that 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 3171-4137 kPa (460-600 psi). Any condition that causes the valve to open should be corrected, and the refrigerant should be replaced as necessary.

Refrigerant-134a

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 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 (A-12).

This vehicle uses a new type of refrigerant called Refrigerant-134a (R-134a). It is a nontoxic, nonflammable, 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.

Refrigerant-134a carries a charge of a special lubricant, 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.