So I come home today and crank up the thermostat a few degrees and get
on with dinner prep. That's weird, it sure seems a bit chilly when I
sit down to eat my dinner...
Go over to the thermostat, and see that although I hear the blowers
blowing, the red light on the thermostat is not on as it usually is, and
cold air is blowing out the vents.
Trudge downstairs, thinking "ignitor". Poke around there a little, pull
the ignitor but it's solid. Look in the bottom half of the furnace, and
read the "diagnostic" chart, that tells me what the status light on the
circuit board means when it flashes. Re-apply power, both blower fans
go on, but no ignition, and the light is flashing 4 times. The chart
says that means I have an open limit switch. Apparently there are two?
a main and an aux. Try to follow the schematics, and my best guess is
that the main limit switch is connected on red wires, and goes into the
plenum. Pulled it out, and it looks like a tiny little metal drum on a
There are 3 other little drums that are in the front of the furnace,
kind of flush with the bottom, and each has little switches connected to
them. I pressed each one a few times, but that didnt' make a
difference. Light purple wires on those. Aux Limit Switches?
how much more can I DIY before I call in the big guns? Looks like the
mail LS runs about $35? Worth it to just change it out?
this is a Goodman GMP125-4, I'm thinking circa 1996, since the SN starts
thanks for any tips/info.