Short cycling
Also known as: frequent starts, rapid cycling
Short definitionThe compressor cutting in and out again and again at short intervals. Each start heats the winding, wears the contactor and throws oil into the system before it can return to the crankcase, so compressor life is shortened.
On site it is seen most often with oversized equipment: the room cools quickly, the compressor stops and a little later it starts again. Starting current is several times the rated value, and only suction gas flowing for a while removes the heat from the winding. The manufacturer’s limit depends on the model; at most 6–12 starts per hour are allowed, and run and off times should not be shorter than 2–3 minutes.
On the control side, a differential left as narrow as 0.5 K is opened to 2–3 K, and the sensor is moved away from the supply air and the doorway. If a pressure switch is doing the stopping, the cause lies elsewhere: undercharge or a blocked filter on the low side, a dirty condenser or a stalled fan on the high side. In a pump-down system a leaking solenoid valve also starts the compressor for a few seconds and stops it while the room is cold. A start counter makes the diagnosis easier.