Heat pump thermostat problems

Old 06-30-17, 12:25 PM
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Heat pump thermostat problems

I had what I thought was a simple thermostat installation and have the following problem. Lost 24Vac between the common and red wires/terminals. This is a heat pump with 7 wires with the following terminal - wire list:
G - Green, Y - Yellow, E - Blue, W2 - White, C - Brown, O - Orange, R - Red.
After I connected everything to the new Honeywell terminals and plugged the thermostat; the screen was blank. I called customer service and they said probably not enough voltage to power the new thermostat. I checked voltage between the Common -C and red wire to find no voltage. I reinstalled old thermostat exactly as removed (I have a photo of original) and as expected it doesn't work now because there is no power between C an red terminals. My heat pump is an old Day an Night unit made by carrier. What can be the cause and anything I can do before calling for service?
Old 06-30-17, 12:54 PM
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Check the fuse on the control board in the furnace. If you didn't shut off the power to the furnace you probably shorted the wires.
Old 07-09-17, 08:28 PM
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Check low voltage fuse may be when you try to install the new thermostat you touch by accident common and hot wired by accident and shortage the low voltage I hope this help thanks
Old 07-09-17, 09:11 PM
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Welcome to the forums.

We haven't heard back from the OP in a while so maybe he figured out the problem.

Since he has a heat pump he's not likely to have an actual control board like a furnace would have. He could possibly have a fuse but more likely the transformer has been shorted and is fried.

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