Test a thermal switch (aka high limit switch) on a DESA brand propane construction heater.

The thermal switch is a safety device that will shut the heater down once the ambient temperature reaches approximately 85 degrees fahrenheit.


According to the manufacturer, DESA International:

To check switch, set the ohmmeter on the “RX1” scale. With heater cool,

check for continuity across the thermal switch by attaching the ohmmeter to the

blue wires on switch. The ohmmeter should read "hot" until the ambient temperature reaches 85F, at which time the meter will read "dead".

If the switch shows "dead" at any other temperature range, then the part is defective and should be replaced.

(Note: this test must be performed in an area that is cooler than 85 degrees F)