Coleman 9420-381 RV Thermostat Voltage Drop: Complete Repair Guide & Solutions
Pulled the same wire swap trick that fixed my old analog RV thermostat's voltage drop, but this new Coleman 9420-381 digital replacement is behaving completely different. Everything worked great all summer with the AC, but now that heating season is here, I'm having major problems.
The furnace keeps short-cycling terribly - the burner fires for maybe 3-20 seconds, shuts off, then the whole cycle repeats. I've already ruled out the furnace itself (replaced the board, checked sail switch and limit switch). Through testing, I discovered the furnace is steady at 13.4V, but when the thermostat calls for heat, the voltage it sends back slowly drops from 13V down to around 10V, then the burner shuts down.
If I short the two furnace wires directly, the furnace runs perfectly. I suspect the thermostat's solid state components are failing. I'm wondering:
1 Has anyone else seen this issue?
2 Are others using this 9420-381 thermostat without problems?
I really like the digital features, but need a reliable solution. …more
The furnace keeps short-cycling terribly - the burner fires for maybe 3-20 seconds, shuts off, then the whole cycle repeats. I've already ruled out the furnace itself (replaced the board, checked sail switch and limit switch). Through testing, I discovered the furnace is steady at 13.4V, but when the thermostat calls for heat, the voltage it sends back slowly drops from 13V down to around 10V, then the burner shuts down.
If I short the two furnace wires directly, the furnace runs perfectly. I suspect the thermostat's solid state components are failing. I'm wondering:
1 Has anyone else seen this issue?
2 Are others using this 9420-381 thermostat without problems?
I really like the digital features, but need a reliable solution. …more