Here are some pictures of the new hi limit switch install and the tests to follow it.
With the furnace out of the camper, this is easier but the hi limit switch is buried pretty deep.
The old discontinued hi limit switch. It has #4 screws with a #0 square bit drive head. Odd, on this whole furnace this is the only square drive head screw.
The new hi limit replacement. PN 37022
The terminals are rotated some and smaller.
The bench test after installing the switch and the outcome.
I used steel plates to block off all 3, 4" duct holes. Two of the plates has some holes drilled in them that allowed limited air flow. I would estimate I was 95 to 98% blocked on the three duct ports.
The test outcome. This is a 20,000 BTU furnace. Time zero was when the gas burner opened the first time. I used the same remote thermometer to measure the inside cabinet air temperature at the hi limit switch area. The old switch had ratings stamped on it, set point 190F, with a -20F differential.
Start
Time" 0'0" Gas burner on
Hi limit area temp: 57F
Time: 3' 59" Gas burner off
Hi limit area temp: 204F
Time: 5' 41" Gas burner on
Hi limit area temp: 154F
Time: 8' 20" Gas burner off
Hi limit area temp: 206F
Time: 10' 10" Gas burner on
Hi limit area temp: 154F
Time: 13' 20" Gas burner off
Hi limit area temp: 204F
Test over.
With blocking the ports more completely, the system will cycle the burner on and off as it should.
The furnace is now ready to install back in the camper.
Thanks again everyone.
John
