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A/C or Furnace (fan) will not come on

3015 Views 6 Replies 3 Participants Last post by  texas115115
The thermostat is a fairly new digital one that runs on batteries and I have verified that the thermostat is working. I tied the wires on the back of it (to bypass the t-stat) and nothing still came on - fan or A/C unit. I can hear the T-stat click when I lower the temp on it - but that's it. There are no tripped breakers or fuses at the panel. I checked for loose or burnt wires and don't see any.
I am not sure how to verify that everything is getting power as it should. I have a Ducane Gas furnace (blower) that has a Honeywell circuit board on it. I have a multi-meter but am not sure what to test and where.

thanks Rob
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test for incoming power at furnace.Test for control power 24v at control board r-c make sure the door switch is in on ducane i believe all you have to remove is middle door section. no power, test incoming on xmfr 120v and secondary 24v. If power is good leaving xmfr look for a small fuse on board.
Well, I looked at the circuit board and sure enough there was a 5A fuse that was blown. I swapped it out, the unit came on and then immediatly blew the fuse again.
Any suggestions?

good indication you have a low voltage short disconnect all tstat wires and replace fuse
good indication you have a low voltage short disconnect all tstat wires and replace fuse or disconnect all tstat wires from furnace and tstat and ring out wiring with multimeter make sure wires are not touching:yes:
If continues you will need to trace the low voltage circuit further for shorts. You can follow the diagram on panel door.
Qbert is right about wire digram

But I would look at the t-stat wires for bare spots. Although when you installed the new t-stat you probley let two wires touch and just need to space them out. Good luck.
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