When refrigeration systems are exposed to low outside air temperatures, the condensing pressure will fall, and if the head pressure gets too low, the metering device will not have enough pressure drop across it to operate properly. The metering device will then underfeed the evaporator, and a low pressure will result in the evaporator, which can cause refrigeration systems to short-cycle from the low-pressure control opening prematurely. Also, once the refrigeration system is off, it may never turn back on again, because the evaporator pressure may never reach the cut-in pressure of the low-pressure control.
Condensing units that are exposed to low ambient conditions must have some sort of low ambient control installed on them to prevent their head pressures from falling too low. However, before getting into the low ambient controls for condensers, let’s review the functions of a refrigeration system’s condenser.