Bimetal or capillary switch that starts the cooler fan above a set oil/air temperature on cycling-fan packages.
Also called: fan thermal switch · temperature switch
De-energised state: NO
Normally open, closes on rise (typical). Some machines use close-on-fall NC types for heat-recovery dampers — read the tag.
How it works
A snap-action thermal switch mounted on the airend discharge or cooler header closes its contact at the set temperature to start the fan motor contactor, and reopens on a fixed differential.
Specifications
- Typical set point
- Closes 180 – 200 °F, opens ~20 °F lower
- Contact rating
- Pilot duty, 10 A @ 240 VAC typical
Parts you can order
- $30 – $130Generic industrialCooling fan thermostat switchBy set temperature and switch action
Field test procedure
- Ohm across the switch cold: NO type reads OL. Heat the sensing element and it should snap to < 1 Ω.
- Compare switching temp against an IR reading at the sensing point.
Symptoms & probable causes
- High temperature trip with a cool coolerFan switch not closing or fan contactor coil open.
- Fan runs constantly, oil never warmsSwitch welded closed.