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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I just installed a new honeywell WiFi thermostat. I didn't

Customer Question

I just installed a new honeywell WiFi thermostat. I didn't have a c wire for the thermo so I moved the g to c on both the thermo and the furnace. I also jumped the g to y with 18 gauge wire. The blower will kick on but the outside compressor will not turn on. Any ideas why the compressor won't turn on?
Submitted: 2 years ago.
Category: HVAC
Expert:  Phil replied 2 years ago.
Hello, By moving G to C you caused a direct short from the + side of the 24vac source transformer to the -(minus) side for lack of better terms, that would have blown out the printed circuit board inside the NEST thermostat in most cases... we will have to do some tests on that.... it would also have blown the 3 amp automotive type fuse on the printed circuit card mounted to the furnace blower. (most have that fuse). Put the G wire back on G, look for a blown fuse in the printed circuit card for now so we can keep track of it all, remove the jumper between Y and G. If we are lucky, you can get this going by running a wire from C on the printed circuit board and C on the thermostat... look on the thermostat wire bundle for one or two unused wires that might be cut short or wrapped around the end of the bundle. Let me know what you find, we can go from there.
Customer: replied 2 years ago.
Furnace blower fuse does not appear to be blown. I don't think it's a blown fuse causing an issue.
Expert:  Phil replied 2 years ago.
Hello again, It may very well not be a blown fuse causing the issue, it is just one the many things we must look at... it would be crying shame to spend an hour checking a bunch of things, only to find out we had not verified the fuse. Did you find any spare wires in the thermostat wire bundle that ends up inside the furnace... if not, you are going to have to pull one by fishing it through the wall most likely. Let me know about that, we can go from there.
Customer: replied 2 years ago.
I can't find any extra wires.
Expert:  Phil replied 2 years ago.
Thanks for looking,
If you can post a photo of the thermostat wire bundle as it enters the furnace I can take a look for an extra wire myself. I need to see the wire from the point it enters the furnace until each wire in the bundle attaches to the printed circuit card.
Use the 'attach files' link at the bottom left to do that with.
Your other option is to pull the extra wire... tell me how far the thermostat is from the furnace or air handler so that I can coach you on how to do that if needed.