A/C Metering Devices

Cycling clutch switch on the accumulator.

A (CCOT) cycling clutch orifice tube system has an accumulator and a cycling switch attached. The accumulator is located on the low side of the system, after the orifice tube.

A (TXV) thermostatic expansion valve system has a receiver drier located on the high side of the system, between the condenser and the expansion valve. Both of these devices are dryers containing a desiccant to clean and absorb moisture from the refrigerant.

At first glance, a (CCOT) cycling clutch orifice tube system has an accumulator and a cycling switch attached. The accumulator is located on the low side of the system, after the orifice tube. A (TXV) thermostatic expansion valve system has a receiver drier located on the high side of the system, between the condenser and the expansion valve. Both of these devices are dryers containing a desiccant to clean and absorb moisture from the refrigerant.

Fixed orifice tube

They also use a different method of metering refrigerant into the evaporator core. An (FOT) fixed orifice tube meters the same fixed amount of refrigerant based on the diameter of the tube inside its casing. A cycling clutch switch is used to engage and disengage the compressor clutch according to the system's low side pressure.

Orifice tubes can become clogged and severely hamper A/C performance. It's essential to replace the old tube with the correct tube. Follow the manufacturer's recommendations. Some aftermarket companies offer a variable orifice tube that claims to improve performance, especially at red lights and stop and go traffic. Always check and follow the manufacturer's recommendations.

A/C evaporator core sensing bulb location.

The expansion valve above contains a small needle valve and diaphragm that's attached to a sealed gas chamber. Temperature causes the gas in this chamber to expand and contract, resulting in movement of the valve. This needle valve opens and closes to allow refrigerant into the evaporator core. As temperatures rise, the valve opens, allowing more refrigerant into the evaporator. As it cools, the valve closes, restricting the flow of refrigerant into the core. This device provides optimum cooling while preventing evaporator core freeze up.