Auto A/C Terms - Glossary
Ford Fixed Orifice Tube - FFOT system

Like the Cycling Clutch Orifice Tube A/C system that General Motors developed in the late 1970s, the FFOT system is designed in much the same way.

FFOT systems utilize a fixed orifice tube opening in place of a typical thermostatic expansion valve. On expansion valve systems, the valve uses a sensing bulb to monitor the evaporator outlet temperature and then open or close the flow of refrigerant into the evaporator. On a system using a fixed orifice tube, there is always a flow of refrigerant into the evaporator. The A/C compressor cycles on and off in order to control the flow of refrigerant.

The other major difference is that typical A/C systems using thermostatic expansion valves or TXVs, also include a liquid line receiver drier. It is typically mounted in the line between the condenser and the expansion valve inlet. On FFOT of fixed orifice tube systems, the receiver drier is eliminated and replaced by a low side accumulator. The most common mount position for the accumulator is at the evaporator outlet. If not attached to the outlet of the evaporator, it will be mounted in line between the evaporator and A/C Compressor suction inlet.