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I have a carrier furnace 2008, just changed my old thermostat to new nest thermostat, forgot to turn off the power. Now I have no power on my r line, checked short fuse still good, red light in front of furnace still on, I am not sure why I lost power to the r line. My furnace was working fine yesterday. Checked with nest supporting line, nest base was not a problem. Help

  • If you jumper R to W, does the furnace run? – ThreePhaseEel Dec 2 '16 at 12:48
  • How are you checking for "power"? Do you mean that the thermostat does not turn on, or that you're not measuring 24 volts on the wire? How did you wire the new thermostat? Does the thermostat need a C wire? If so, did you hook up a C wire? – Tester101 Dec 2 '16 at 15:52
  • I crossed the r and c wire, furnace did not turn on, – Trien Dec 3 '16 at 2:02
  • Yes I need the c wire. I connected the wire to the thermostat correctly. The r wire has low voltage. The red light in the control panels blink when I crossed the r and c wire. The blinking frequency usually tell how to trouble shoot for the problem. – Trien Dec 7 '16 at 14:54
  • Do you mean you're crossing R and W @Trien ? – ThreePhaseEel May 18 '18 at 22:36
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check for 24 volts at the furnace. Some carrier boards will have a lit led even if the 24 volt circuit is non functioning. I don't recommend using a contact probe. I always recommend using a muti-meter. Check from R to C. your looking for 24 volts. if no voltage, then check 3/5 amp fuse on board. If fuse is good, check voltage from transformer. If you do have voltage From R to C. put a jumper from R to G and see if the fan comes on. if fan comes on, then you know the issue is at the thermostat somewhere.
I hope this helps..

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