Thermostat/Furnace/Heat Pump not working

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Old 02-11-15, 01:05 PM
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Thermostat/Furnace/Heat Pump not working

Hi and thanks in advance for the help!

We noticed a few days ago that our heat pump and furnace weren't working. The thermostat, said "Aux heat" but the furnace would not be on. The problem was discovered while I was trying to find the cause for a breaker to have tripped (and kept tripping) that controlled most of our finished basement's ceiling lights. I don't know if the problems are related, but I was able to locate the short (a faulty wire in our crawl space) and now the lights are back on, but the heat is still off.

My gut says it's either a problem with the thermostat wire or the thermostat. The furnace and pump's power supplies are both working, though we currently have the breaker located on the furnace turned off as it keeps blowing a fuse whenever we turn it on.
I get no voltage reading with my analog multimeter on the thermostat wire (I do not consider myself an expert multimeter user, but I must have been using it correctly because it helped me diagnose the faulty wire the other day), and when I check resistance it seems to show a short. When testing the thermostat on the round battery-looking thing on its board, that seems to show a short as well (in this instance, I'm not sure I'm doing it correctly).

When checking resistance on the thermostat wires on the furnace, they all seem to be showing a short.

I believe both furnace and heat pump are Carrier and the thermostat is a honeywell. I'm attaching pictures of all of the stuff I think may be related.

Thanks again.

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heat pump interior
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seems corroded, possible issue?
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heat pump wiring
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heat pump info sheet
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thermostat wiring
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thermostat interior
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where I tested for continuity
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furnace/thermostat wiring
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furnace info sheet
 
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  #2  
Old 02-11-15, 01:15 PM
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we currently have the breaker located on the furnace turned off as it keeps blowing a fuse whenever we turn it on.
If the main (60A?) breaker on the furnace is tripping, then I would say the problem is with the furnace. You may have fried the control board. Maybe the transformer is toast, which would be an easy fix.
 
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Old 02-11-15, 02:20 PM
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I should clarify, neither the breaker on the electrical panel nor the breaker on the actual furnace trips, only a fuse on the furnace blows out.
 
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Old 02-11-15, 07:06 PM
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Update:
I spoke to an HVAC guy who said that I was so close, that he'd just walk me through the rest. Basically, he had me take all of the thermostat wires out of the furnace, replace the fuse and then put them in one by one until I found the one with the short. I did and it was the red. He had said to then pick an unassigned wire of a different color and put it in the appropriate places in the thermostat and the heat pump. I did the thermostat and furnace and, sure enough, the furnace started working! A few minutes later I replaced the wire in the heat pump (I saw a small spark when i initially touched the new wire to it's new home, but not when I screwed it in). When I went back inside, the furnace was no longer on and the fuse has blown again (breakers had not tripped).
I don't know where to go from here.
 
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Old 02-11-15, 08:55 PM
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That's a battery.... nothing to check for there.

He was on the right track....almost. When checking using that method.... you disconnect all the wires but the red wire and then you connect them one at a time. I'm going to guess and say it's the yellow wire for the compressor.

It's pretty rare for the thermostat wiring to have a short. It is very common for the wiring to the outdoor unit to have a short.

Identify the cable going to the outside unit..... disconnect the red, black and yellow wires at the air handler.... not outside and try the system again. This will temporarily disconnect the outside unit.
 

Last edited by PJmax; 02-11-15 at 09:16 PM. Reason: added troubleshooting info
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Old 02-12-15, 08:46 PM
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Thanks for the info. Apparently, my defrost panel is fried and i need to get a new one. Oh well....
 
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Old 02-12-15, 08:54 PM
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At least you know what the problem is now. It's worse not knowing and guessing.
 
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Old 02-12-15, 09:34 PM
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Exactly. The HVAC guy I had come over said that he had never seen anyone troubleshoot like I had so he just told me what I needed to get and that I'd easily be able to replace it myself and it would be cheaper for me to find one online than for him to order it.
How often does THAT happen?
 
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