Figure 13-7. - Thermostatic switch.

Thermostatic Switch

This system uses an electrically operated switch (fig. 13-7) to engage and disengage the compressor. The switch is operated by a sensing bulb placed in the airstream after the evaporator. As the evaporator temperature falls, the thermostatic switch opens to disengage the magnetic clutch in the compressor. When the coil temperature reaches the proper level, the switch again closes to engage the clutch and drive the compressor.

Hot Gas Bypass Valve

The hot gas bypass valve was used on some older models to control evaporator icing (fig. 13-8). The valve is mounted on the outlet side of the evaporator. The high-pressure gas from the compressor joins with the low-pressure gas exiting the evaporator. These two gases mix, causing a pressure increase. Also, the boiling point increases which results in a loss of cooling efficiency. This, in turn, causes the evaporator temperature to increase, thus eliminating freeze-up. The compressor is designed to run constantly (when it is activated) in the hot gas bypass valve system.

Suction Throttling Valve

The suction throttling valve (fig. 13-9) is used now in place of the hot gas bypass valve system. It is placed

Figure 13-8. - Hot gas bypass valve.