I have a Honeywell model number NHGK076AF01 propane furnace. It is about 15 years old. The problem started when I noticed the breaker had tripped and I had no heat. After resetting breaker, I tried again. Everything goes as it should except when time for blower fan to come on. It doesn’t come on if in "auto" mode but if I put it in the "on" mode, the blower comes on and I have heat.

I replaced the limit switch L170-40 and still have the same problem. There is another limit switch in the blower area L140-40. I checked this one with ohm tester and it seemed OK - it was closed tester beeped. I am scared to let it run too long - two minutes maybe - and when the blower doesn't come on, I set to "on". Another thing is I'm not sure if it would trip the breaker again if I didn’t turn the blower on instead of limit switch turning everything off. I'm not sure what else to try. Funny the blower works in "on" position and not "auto". Thank you for taking the time to read.enter image description hereenter image description hereenter image description here

  • I had a similar problem several months ago - house wasn't warming up much, found that furnace would go on but blower wouldn't and after a few minutes of running, furnace would turn off - presumably due to some high temperature limit being triggered by the heat not being dissipated by blowing air. In my case, it wouldn't run in "fan always on" mode either. I couldn't figure it out and called in my regular HVAC guy. He had to replace a board and for the day before he could do that, he hardwired the blower to stay on, bypassing whatever controls had failed. – manassehkatz-Moving 2 Codidact Feb 8 '19 at 18:28
  • Thanks I have thought that just wanted to see if anyone else had the same problem I believe it either the board or maybe capacitor on blower fan – Lee Decker Feb 8 '19 at 18:56
  • My hunch (but I am not an HVAC pro) is that the fan is fine because it works in "on". And not the thermostat since it calls for heat and at that point the fan is under furnace control. And probably not a limit switch because the system (from what you've described, and similar to what I experienced) runs despite not having the blower running. So that points to a relay or something on the furnace board that is supposed to turn the blower on, but isn't doing its job. – manassehkatz-Moving 2 Codidact Feb 8 '19 at 19:03
  • My hunch (and I'm also not an HVAC guy) is that the blower is a 2-speed motor. On "Auto" the blower uses the low speed, and on "On" the blower uses high speed, and the circuit breaker popping was your low speed windings giving their last farewells. – Duston Feb 8 '19 at 22:07
  • Can you post the wiring diagram for your furnace? Google seems to not be able to find a service manual for it... – ThreePhaseEel Feb 8 '19 at 23:46

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