System Diagnosis - Cycling Clutch Orifice Tube (CCOT)

The Cycling Clutch Orifice Tube (CCOT) refrigerant system is used on vehicles that are equipped with 4.3L engines. The CCOT refrigeration system cycles a compressor on and off. the cycles maintain desired cooling and prevents evaporator freeze-up. Passenger compartment comfort is maintained by selecting the following on the control assembly:

- The mode.
- The fan speed.
- The air temperature.

The refrigeration cycle is controlled by a switch that senses low-side pressure as an indicator of evaporator pressure. The switch is the freeze protection device in the system that senses refrigerant pressure on the suction side of the system. The switch is located on the low-side service fitting, which is standard for this system. The equalized pressures within the charged air conditioning system close the contacts of the pressure switch when the air temperature is between 16°-26°C (60°-80°F).

Voltage is supplied to the compressor coil switch when an air conditioning mode is selected. The compressor reduces the evaporator pressure to approximately 175 kPa (25 psi). The pressure switch then opens which de-energizes the compressor clutch. As the pressure system equalizes and the pressure reaches approximately 315 kPa (46 psi), the pressure switch contacts close. This re-energizes the clutch coil.

Under certain conditions, cycling may cause increases and decreases of engine speed. This is a normal condition. The system is designed in order to maintain desired cooling, which prevents evaporator freeze-up.

The operating characteristics of the low-side pressure cycling switch provides additional compressor protection. Low-side pressures could be insufficient to close the contacts of the pressure switch under the following conditions:

- A massive discharge occurs in the low side of the system
- The orifice tube becomes unplugged

If a low charge occurs, insufficient cooling accompanied by rapid compressor clutch cycling will be noticed at high air temperatures.

When the engine is turned OFF while the air conditioning system is operating, the refrigerant in the system will continue to flow. The refrigerant will flow from the high-pressure side of expansion tube (orifice) to the low pressure side until the pressure is equalized. The equalization can be detected as a hissing sound for 30-60 seconds. This is a normal condition.