Dryer outlet temp sensor probes:
The Fenwal sensor can deform over time and cause a lower setpoint for fire declaration. This causes a sprinkler trip when there is no fire.
The Fenwal sensor is made with a hex pipe bushing and a copper tube. In some cases, the tube has been found bent after long term use either by defect or possibly goods hitting the probe, causing a lower setpoint in the switch.
If false trips are suspected, remove the Fenwal probe. See the location called "outlet probes" below. These probes are on the top of the dryer discharge duct.
Dryer outlet probes
If the probe appears bent...where the hex bushing is not perfectly straight with the barrel of the sensor...replace the sensor.
The working part of the probe uses bimetallic materials that are preset at the Fenwal factory. The elongation of the probe lowers the setpoint and causes false trips.
Replace the probe. Never adjust the setpoint! Adjusting the setpoint will potentially raise the trip point above the proper setting and allow a fire that could destroy the dryer and laundry!
New Fenwal sensor:
Fenwal sensor internal parts and switch element:
Smart fire sensing...
In addition to the probe above, the normal outlet temp probe is monitored by software and an output on the dryer can trigger the sprinkler.
This system uses a simple method by looking at the gas valve position and outlet temperature. If the gas valve is commanded to position 000 and we see a rising outlet temperature, then we assume a fire and either terminate the step or if needed trip the sprinkler. If the outlet exceeds 220 then the heat steps are terminated.
These events are recorded in the dry cycle details. So, after a sprinkler trip...if the dryer remained on...the termination of the step should show an error message indicating the reason for terminating the dry cycle. If the step terminates with a three wire disabled, then you can assume the Fenwal probe tripped the sprinkler, or someone tripped the sprinkler manually.
If the outlet temp exceeds 240 degrees F then the dryer software declares a fire and trips the sprinkler.
Dry Cycle details can be viewed in DryNet (from the menu) or from the display on older dryers with individual keypads and displays. If the dryer power is turned off, the dryer may not record the event.
