Low-Pressure Cutout Switch
A low-pressure cutout switch is similar in design to a high-pressure switch (see previous section) except that it provides low-pressure cutout protection.
As shown in Figure 6-70, this switch is connected to the so- called low side of the compressor and is designed to open the compressor power circuit if the low-side pressure drops below a desired level. These excessively low pressures are usually caused by dirty filters, evaporator fan failure, a stuck damper, damper motor failure, or some other interruption in the air supply.
The cutout action of the switch prevents the temperatures in the evaporator from falling below the temperature at which frost would form on the coils. It also prevents the feeding of an excessive amount of liquid to the compressor. Low-pressure cutout switches may be designed to provide either manual or automatic reset.