(CCOT) Refrigeration System

CYCLING CLUTCH ORIFICE TUBE (CCOT) REFRIGERATION SYSTEM

CAUTION: Avoid breathing A/C Refrigerant-134a (R-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 manufactures.

The sole function of the refrigeration system is to maintain an evaporator core outside temperature between approximately -1°C and 9°C (30.5°F and 49°F) when refrigeration is required. The major components are the compressor, condenser, evaporator, expansion (orifice) tube and the accumulator. The components are interconnected by hose and tubing connections. This system incorporates the cycling clutch expansion (orifice) tube-type refrigeration system called CCOT.

The refrigeration system is controlled by the Air Conditioning Programmer or ACM (Air Control Module) and the Powertrain Control Module (PCM) with input from a low-side refrigerant temperature thermistor which turns the compressor "ON" and OFF" as required to prevent evaporator condensation freeze. The compressor runs only as much as necessary, resulting in fuel savings and less engine strain. An explanation of the refrigeration cycle and a brief description of each component follows:

^ During cooling operating conditions, slight increases and decreases of engine speed/power may be noticed. This characteristic should be considered normal as the system is designed to cycle the compressor on and off to maintain desired cooling. This reduced compressor operation benefits fuel economy.

^ The compressor low-pressure switch protects the compressor from operating if a low-charge condition exists. Additional compressor protection comes from the operating characteristics of the CCOT system. If a partial low-charge condition exists, or the expansion (orifice) tube becomes partially blocked, low-side pressure could be too low (cold) to allow the Air Conditioning Programmer (ACM) to turn on the compressor clutch for a "normal cycle." This will be evidenced by rapid compressor clutch cycling and relatively warm air being discharged from the A/C outlets. If these conditions occur, the system should be repaired before compressor damage occurs. If the charge drops to 1/4 of full charge, the ACM will disengage the compressor.

^ When the ignition is turned "OFF" and the air conditioning has been operating, the refrigerant in the system will continue to flow until pressure is equalized. This may result in a faint sound of liquid flowing for 30 to 60 seconds and should be considered normal.

^ An anti-slugging feature is incorporated which will remove liquid refrigerant that may collect at the compressor. This operation will normally occur once a day after prolonged (overnight) soak of several hours. On initial crank, the Air Conditioning Programmer (ACM) will check for indications of this condition and if found, the A/C clutch will engage. After the engine is started or shortly thereafter, the clutch will disengage and wait until the normal calibrations and parameters are met to signal engagement of the clutch.






REFRIGERATION CYCLE
The compressor discharges high-temperature, high-pressure vapor that contains heat absorbed in the evaporator, plus heat imparted to it by the compressor in the compression process. This vapor flows through tubes in the condenser where it releases heat to the airstream and changes to a medium-temperature, high-pressure liquid. This liquid flows through the liquid line to the orifice tube where it undergoes rapid expansion and changes from a medium-temperature, high-pressure liquid to a low-temperature, low-pressure liquid/vapor mixture. This cold, foamy refrigerant mixture enters the evaporator core at the bottom and flows through parallel tubes upward through the "U" flow core. Heat from the warm airstream passing through the core is transferred to the refrigerant, vaporizing the liquid and cooling the air. Under high-load conditions, all the liquid is vaporized in the evaporator and only heat-laden vapor flows to the accumulator and through the suction line to the compressor, where the cycle is repeated. Under lighter load conditions, the liquid and vapor are separated in the accumulator so that only vapor is drawn into the compressor.





Compressor
The vehicle uses an HD-6 compressor which is a 10 cubic inch displacement six cylinder axial-type mechanism consisting of three double-ended pistons actuated by a swash plate shaft assembly. The compressor is located on the lower right of the engine centerline (right-front corner of the engine compartment), and is belt-driven from the crankshaft pulley. The compressor performs two main functions. It provides pressure and temperature levels at which heat exchange can take place in the condenser by compressing the low-pressure refrigerant vapor from the evaporator into a high-pressure, high-temperature vapor. It also pumps refrigerant (and refrigerant oil) through the A/C system.

A magnetic clutch is used to engage the compressor shaft. when voltage is applied to the clutch coil (by closing contacts in the thermostatic switch), the clutch plate and hub assembly (which is solidly coupled to the compressor shaft), is drawn by magnetic force rearward toward the pulley which rotates freely on the front head casting. The magnetic force holds the clutch plate and pulley together as one unit. The compressor shaft then turns with the pulley. When the PCM removes the voltage from the clutch coil, springs in the clutch plate and hub assembly move the clutch plate away from the pulley and the clutch plate and compressor shaft cease to rotate.





High-Pressure Relief Valve
The compressor has a pressure relief valve that opens and allows refrigerant to vent off to the atmosphere when high side pressure exceeds 3,620 + 571 kPa (525 + 75 psi.). This is done to prevent system damage. Any condition that causes this valve to open should be corrected and the refrigerant oil and refrigerant should be replaced as necessary. Refer to Refrigerant Oil Distribution.


Condenser
The condenser assembly, mounted in front of the radiator, receives high pressure, high temperature refrigerant vapor from the A/C compressor. The condenser is made up of aluminum tubing and cooling fins which allow rapid heat transfer away from the high-pressure, high temperature refrigerant vapor and causes it to condense into a high-pressure, medium temperature liquid.





Expansion (Orifice) Tube
The expansion tube restricts the flow of high-pressure, medium temperature liquid refrigerant from the condenser. As the high-pressure, medium temperature liquid refrigerant passes through the expansion tube, it expands to become a low-pressure, low temperature liquid/vapor mixture.

The expansion (orifice) tube consists of a small brass tube molded into a plastic holder, with fine mesh screening protecting both ends of the tube. The expansion tube is installed inside the evaporator inlet refrigerant line where it connects to the condenser outlet. The expansion tube is serviced as an assembly by replacement only.

When the engine is turned off during A/C system operation, refrigerant in the system flows from the high side of the system to the low side through the expansion tube until pressures equalize. This may be detected as a hissing sound for 30 to 60 seconds after shut down, and is normal.

Evaporator Core
The aluminum evaporator core is located along the right-hand side of the cowl, and is the actual cooling unit of the system. The blower forces air through the evaporator core, where it is cooled and dehumidified. Condensation, which collects on the cold fins of the condenser, is drained from the housing through a small hole in the module bottom. Unlike a radiator which transfers heat to the air flowing through it, the evaporator core absorbs heat from the passing air. This is how the air is cooled. The heat that is absorbed from the air causes most of the refrigerant to boil into a vapor.

This vapor then flows out the top of the evaporator and into the accumulator, carrying with it some liquid refrigerant and refrigerant oil.





Accumulator
Refrigerant leaving the evaporator flows into the accumulator, which acts as a holding tank and separates any remaining liquid refrigerant from the vapor. Refrigerant oil also collects in the accumulator. At the bottom of the accumulator is a packet of desiccant, which absorbs and holds any moisture that may have entered the refrigeration system. This desiccant is specifically designed for R-134a.

Refrigerant exits from the top of the accumulator to insure that no liquid refrigerant enters the compressor. An oil bleed hole in the outlet pipe provides a path for lubricating oil to reach the compressor.
The accumulator is serviced as an assembly by replacement, but should ONLY be replaced when the shell is perforated and a refrigerant leak is found, or if the system has been open for a prolonged period of time (greater than 24 hours).

Accumulators for R-134a systems have metric fittings identified by a grove cut into fitting flats. Replace only with like Accumulator or thread damage will result.





Heater System
The heater system heats air entering the vehicle passenger compartment. The main component of the heater system is the heater core, a small radiator located inside the passenger compartment. Engine coolant is pumped to the heater core directly from the engine whenever the engine is running; no water valve is used. The engine coolant transfers heat to the heater core tubes and fins; air passing over the fins on its way to the passenger compartment then absorbs this heat.