High Limit Switch | Thermostat

A high limit switch is a control device made of two dissimilar pieces of metal (a bi-metal) that flex at a very specific temperature. When used on an electric dryer it is often positioned in close proximity to the dryer heater. In the event of a dryer vent restriction the high limit t stat opens the circuit to the heater reducing the possibility of a dryer fire.

Dryer high limit thermostats are safety devices and in the event that it should be in the open position something is wrong with the dryer. It could either be a shorted heater, or more likely a dryer vent restriction. Nevertheless whenever you find a high limit thermostat in the open position it needs to be corrected.

A typical high limit switch is the dryer high limit thermostat part number 3204267. It has an operating range of 260 to 270 degrees fahrenheit. It is used on Kenmore, Frigidaire, and some other brand dryers and laundry centers. Other part numbers for this item are, 508516, AP2131477, PS446428, PT6394431

Technicians check high limit thermostats by using an ohmmeter to check for continuity if they suspect the high limit switch is the problem. The difficulty with that is there's always going to be continuity on a perfectly functioning high limit thermostat. Remember the thermostat contacts open in the event of an anomaly such as a vent restriction.

Experienced technicians use a voltmeter to check a high limit thermostat while the dryer is operating. If a high limit thermostat opens too soon it's going to interrupt the circuit to the heater and the problem will be not enough heat in the drum. By using a voltmeter across the contacts you can see when the contacts are open or closed. Went the contacts are closed, the voltmeter will read it zero. Went the contacts are open the voltmeter will be 220 Volts.

This should not be attempted by an inexperienced person. Only experienced service technicians who are familiar with the process should attempt to check voltage while an appliance is operating.