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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 852
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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I have a Lennox G12Q4-110-4 furnace with 2 issues: 1) Burner

Customer Question

I have a Lennox G12Q4-110-4 furnace with 2 issues: 1) Burner won't stay lit long, 2) Blower fan runs constantly. I think the Camstat FALTS57E-13T-110-160 switch is bad, but I'm not certain. In normal condition, the burner will come on for about 1 minute, then stay off for about 3.5 minutes. This cycle is continuous, and with cold outside temps lately (~20 degF), it can't keep up with the heat loss. I determined that it is the Camstat switch that is cycling the burner on and off. I jumpered terminals 5 & 6 to keep the burner lit. That worked good, and it will operate on the room thermostat. I am concerned about leaving the jumper on, because I don't know if I am actually getting it too hot. I don't think I am, but I want to be certain. After running for 10 minutes or so, the nearest outlet was at 162 degF, with a return air temp of 81 degF. That's a rise of 81 degrees, and the furnace says the air rise should be 45-75 degF. Does this sound like the camstat switch is bad? I pulled it out last night and found it very dirty (a few moths stuck in it), but apparently operable. I would like to replace it, but don't want to waste my money if I should be looking elsewhere.
Submitted: 1 month ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 1 month ago.

Hi I'm Brian and I'm here to help!

It sounds like your fan & limit is doing its job! An 81 degree rise is high. You should check your air filter, your blower wheel and if you have an ac a-coil on your furnace, check that too, check that they are all three clean. With that high of a rise, it sounds like one or more are dirty! I wouldn't leave the limit jumped out, that can be dangerous!

Let me know if I can help further.

Thanks,

Brian