- Condition: The dryer has detected the temperature in the heating chamber in excess of the setting of the thermostat monitoring the chamber.
- Alarm Action Taken: SHUT DOWN
- Component: Manual reset adjustable thermostat
- Location: The body of the thermostat originates in the junction box up inside the dryer inside of the square ductwork mounted just inside the lower access door under the burner. The sensor runs outside the airduct into the heating chamber and is then ran vertically usually alongside of the internal access ladder in the heating chamber.
Tools Required for Service:
- Voltage/continuity meter
- Small standard blade screwdriver (to open cover and wiring terminals inside)
- 5/16” nut driver (if replacing thermostat)
Tech tip: (115 vac circuit)
The Upper High Limit is an adjustable thermostat (usually 90 – 325 degrees F) that is normally set 40 – 50 degrees above the selected plenum temperature setpoint in the controller. The setting on the thermostat is a manual dial setting on the unit itself up inside the dryer along with the reset bar on top of the unit that must be pushed if the unit is tripped out.
(Use caution entering the dryer!! The upper high limit thermostat indicates a high temperature condition unless faulty or incorrectly set! Use the heating chamber temperature reading as an indicator as to the temperature inside before a person enters the heating chamber of the dryer!!)
Potential causes of this alarm condition:
- A high heat condition caused by one or more of the following:
- Too high of a heat chamber setpoint
- Gas modulating motor has malfunctioned and driven itself wide open
- Butterfly valve damaged with no control of internal disc to regulate gas flow
- Too much gas pressure from vapor regulator
- A fire in the heating chamber!
- Faulty thermostat
- Too low of thermostat setting