Expansion Block/Orifice Tube: Description and Operation
DESCRIPTIONThe 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-up. Passenger compartment comfort is maintained by the temperature select bar on the controller.
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 pressure. During air temperatures of 60-80°F, the equalized pressures within the charged air conditioning system will close contacts of the pressure switch.
When an air conditioning mode is selected, voltage is supplied to the compressor clutch coil. As compressor reduces the evaporator pressure to approximately 25 psi, the pressure switch will open, de-energizing the compressor clutch. As system equalizes and the pressure reaches approximately 46 psi, the pressure switch contacts close, re-energizing the clutch coil.
When the engine is turned Off with the air conditioning 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.