My original compressor unit in the starboard seat locker of my 1984 Catalina 36 Mk 1 was replaced by a "used" unit of unknown vintage. The original unit's fan always cycled on and off in a normal manner. The replacement used unit's fan remains on all the time. It does not matter if the thermostat is calling for cooling or not. Is this normal for some old units or is there something that needs to be fixed?