Air Conditioning Only

DESCRIPTION
The Cycling Clutch Orifice Tube (CCOT) refrigeration system is designed to cycle a compressor on and off to maintain desired cooling and to prevent evaporator freeze. Passenger compartment comfort is maintained by the temperature lever on the heater and A/C control assembly.

OPERATION
Control of the refrigeration cycle (on and off operation of the compressor) is done with a switch which senses low side pressure as an indicator of evaporator temperature. The pressure cycling 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 standard Schrader-type valve low-side fitting. During air temperatures of 16-26°C (60-80°F), the equalized pressures within the charged A/C system will close the contacts of the pressure switch. When an air conditioning mode (max, norm, bi-level, defrost) is selected, electrical energy is supplied to the compressor clutch coil. As the compressor reduces the evaporator pressure to approximately 175 kPa (25 psi), the pressure switch will open, 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 maintains 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, thus preventing evaporator freeze-up.

The high-side, high pressure compressor cut-off switch in the rear head of the compressor is a protective device intended to prevent excessive compressor head pressures and reduce the chance of refrigerant escape through a safety relief valve. Normally closed, this switch will open the circuit at a high-side pressure of approximately 2960 kPa (430 psi +/- 20 psi) and reclose the circuit at approximately 1370 kPa (200 psi +/- 50 psi).

Additional compressor protection results from the operating characteristics of the low-side pressure cycling 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.

The compressor, depending upon engine usage, is also cut-off under certain other conditions, such as wide-open throttle, low idle speed, low air temperature and high power steering loads.

Diagnostic charts for the CCOT system are found under System Diagnosis / Procedures, Start at the Functional Test. Testing and Inspection
If replacement of the pressure cycling switch is necessary, it is important to note that this may be done without removing the refrigerant charge. A Schrader-type valve is located in the pressure switch fitting. During replacement of the pressure switch, a new oiled O-ring must be installed and the switch assembled to the specified torque 10 Nm (89 lb.in.).

If the engine is turned off while the A/C system 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 hissing sound for 30 to 60 seconds and is a normal condition.