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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I installed a Wi-Fi thermostat but didn't keep track of the

Customer Question

I installed a Wi-Fi thermostat but didn't keep track of the two wires from exterior unit one red one white. Not sure where on the schematic they belong can you help the ac won't engage and is heating up.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.
I need 2 photo's of the thermostat wire connections where they attach inside the furnace, that also shows red and white wire that runs to the outside unit.
We can go from there.
Customer: replied 1 year ago.
Here's a picture of the inside the unit like I said the red and the white I was unsure of where it hooked up and that's where I have it set right now. If you need I can also open the unit outside and show you where those two wires hook up to
Expert:  Phil replied 1 year ago.
Hello again.
Look that over please, we can go from there.
Customer: replied 1 year ago.
The bottom wire is a C wire. The color is green it is attached to the C spot at the thermostat. When I measured all of the parts only are has 24 the top spot that says twin measures 14 and the rest is nothing. I also did try going straight from Y to C and there was no current as well
Customer: replied 1 year ago.
R had 24 twin had 14 everything else had nothing
Expert:  Phil replied 1 year ago.
Hello again. thanks for data on the C terminal.
It is important to understand that you must measure voltage ***Between** two points with a multi meter for the read to be valid.
I only need to know one thing right now, what read do you get between C and Y with the thermostat set for cooling and down to 55F or at least 5 degrees cooler than the room.
Tell me please which color wires are attached to each terminal on the thermostat please.
We can go from there.
Customer: replied 1 year ago.
Yes 24-26 volts
Customer: replied 1 year ago.
I reversed the polarity at the board from the outside unit and it feels like that may have fixed my problem.
Expert:  Phil replied 1 year ago.
That would be fortunate, but quite unusual, lets dig a little deeper in order to avoid future problem or burning out the the electronics on the printed circuit board or thermostat.
Next tell me you get the same 24-26 volt read where those two wires connect inside the unit outside... if you do and the outside is not running, either the power is off to the outside unit, or the unit has tripped its high pressure cut out switch or other overload, or the contactor coil has failed open.
The other issue, and it is a important issue is that the C terminal has a green wire connected to it, that is supposed to be connected to the G terminal if the themostat is wired standardly... if you got that wrong. you would have created a dead short inside the thermostat between R and C and destroyed the thermostat.
That would have also, blown the fuse in the printed circuit card, and precluded a 24v signal between C and Y that you reported.
I need a photo of the wire connections at the thermostat... that allows me to see the terminal markings for R,W,Y, G, and C
We can go from there.
Customer: replied 1 year ago.
This is not wired standard however the ports on the thermostat match the motherboard so at least they did that
Expert:  Phil replied 1 year ago.
It is wired incorrectly in several aspects
Blue Y from the thermostat should go to Y on the terminal strip... the blue wire at the thermostat obscures which ever marking is there, check that for me please.. do not change anything, that can lead us off into the tall weeds.
I cannot see the terminal letter on the thermostat behind the green wire, can you tell me what that is?
There is no wire on the thermostat from G to G on the terminal strip in the furnace. Hopefully there is a spare wire you can use, if not you need to pull one.
We can go from there. Take your time and be a specific with your wording as possible.
Customer: replied 1 year ago.
white is w green is C Blue is Y and red is r. I do not have any extra wires in that line. On the motherboard there is a jumper wire between y and g
Expert:  Phil replied 1 year ago.
Thanks, ***** ***** non standard but is should work.
If you have 24v between C and Y at the printed circuit board, next step to see if you have 24v between those two wires at the outside unit.
I need a well focused photo of the wiring diagram at the outside unit showing all of the controls and contactor etc.. I can mark that up for you with coaching instructions.