Front A/C Unit

CCOT A/C SYSTEM

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 a low-side fitting. 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 tube (orifice) 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 air conditioning systems that are available for this vehicle are described below:

^ C60-Front Manual Controls, HVAC System
^ C69-Rear Floor Mounted, HVAC System