Gas Furnace Inducer Fan Cycling

[jazz4cash]

The inducer motor on our 20 yr old gas furnace runs intermittently (like 30 seconds every 2 minutes) and cycles back off....as if the pressure switch has failed to signal the burner that is it OK to ignite. I also notice the circulation fan is running constantly while this occurs. At the time the programmable t-stat is set to "auto fan". "cool", temperature set to 77' and room temp is 76'. Compressor runs and cools normally when I change setpoint to 75'. I'm not sure yet if the inducer is cycling like this when the AC is running.

I see several videos and forum posts about problems with the pressure switches but I haven't found any explanation for why the gas starting sequence is being activated in the middle of summer. I did notice this occurred last summer too, but I never got around to doing anything about it. The heating worked fine all winter.

 

[travelover]

I wonder if it is a thermostat problem as in the cool mode it seems like the furnace should not be energized and therefore not go through a sequencing.

 

[Telly]

I agree with travelover.

Either at the thermostat or at the furnace, whichever is easier, you could temporarily disconnect the wire that calls for heat. If the proper color code has been followed, it should be the White wire.

If this stops the draft inducer motor from starting up and running the purge/vent-check 30 second cycle, then the thermostat is the problem.

 

[jazz4cash]

Ok I’ll fool around with the t-stat. Your suspicions are consistent with some speculation on the HVAC expert forum wrt the t-stat draining power causing ghost signals (yeah I know how that sounds). Plus I see the batteries were last replaced in ‘09! Yeah I put them date on ‘em back then I guess. It’s a great tstat-one of the first programmable stats available and I’ve had ‘em in my last 3 houses with no problems. It’s a Lux.

 

[Sunset]

My A/C stopped working, because my t-stat batteries were old.
At first I thought it was a big issue, then I found the batteries, and replaced them and everything worked well.

Now I stick a piece of paper in with the batteries so I know how old they are.

 

[jazz4cash]

Sunset, did your tstat use battery backup or was that the main power source? All ours are hard-wired so the battery is for backup.

 

[Sunset]

Sunset, did your tstat use battery backup or was that the main power source? All ours are hard-wired so the battery is for backup.

My batteries are replaceable, normal AA batteries.
Not hard wired in.