Heating and Air Conditioning: Description and Operation

Refrigeration Cycle:

REFRIGERANT FLOW
The refrigerant flows in the standard patterns, that is, through the compressor, the condenser, the receiver drier, through the evaporator, and back to the compressor.
The refrigerant evaporations through the evaporator coil is controlled by an externally equalized expansion valve, located inside the evaporator case.

FREEZE PROTECTION -- COMPRESSOR CONTROL
When the A/C is switched on, the compressor runs continuously, and the evaporator pressure is controlled by a Suction Throttle Valve (STV) to prevent freeze up.
The refrigerant system is protected against excessively high or low pressures by the dual pressure switch, located on the the receiver drier. If the system pressure rises above, or falls below the specifications, the dual pressure switch opens to interrupt the compressor operation.