Part 1 of 2

GENERAL INFORMATION
This vehicle uses the Cycling Clutch Orifice Tube (CCOT) refrigeration system. This system is designed to cycle the compressor on and off to maintain desired cooling and to prevent evaporator freeze. This carline only uses the manual A/C control (C60).

Pressure Cycling Switch
Control of the refrigeration cycle (on and off operation of the compressor) is done with a pressure cycling switch. It 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.

Compressor Clutch Coil
When an air conditioning mode (Max, Norm, Bi-level, Defrost) is selected, voltage is supplied to the compressor clutch coil. As the compressor reduces the evaporator (low side) pressure to approximately 175 kPa (25 psi), the pressure switch will open, de-energizing the compressor clutch coil. 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 at 1°C (33°F) with slight variation due to outside air temperature and humidity. Refer to A/C Pressure-Temperature Performance chart. Operational Test

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.

Compressor Cutoff Switch
The high-side, high pressure compressor cutoff 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 the safety relief valve. Normally closed, this switch will open the circuit at a high-side pressure of approximately 2760 kPa - 140 kPa (430 psi - 20 psi) and reclose the circuit at approximately 1370 kPa - 345 kPa (200 psi - 50 psi).

Low-side Pressure Cycling System
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.

Low Ambient Temperatures
The same feature that prevents the compressor from operating in the event of a discharge, also prevents compressor operation in low ambient temperatures. When the ambient temperature is below 72-100 °C (45-50°F) the system will not have sufficient pressure to close the contacts in the pressure cycling switch, thus preventing compressor operation.

Compressor Cutoff Conditions
The compressor, depending upon engine usage, is also cutoff under certain other conditions such as wide-open throttle, low idle speed and low air temperature. A/C Electrical System diagnosis is found under Testing and Inspection for the appropriate component.

Pressure Cycling Switch Replacement
Diagnostic charts for the CCOT system are found under Service and Repair. 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 "0" ring must be installed. The switch should be assembled to the specified torque of 10 Nm (88 lbs. in.).

Refrigerant Pressure
When the engine is turned "OFF" with the A/C system operating, the refrigerant in the system will flow from the high-pressure side of the orifice tube 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.