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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Just bought a thermostat and half the wires 't match the

Customer Question

Just bought a thermostat and half the wires don't match the colors on the diagram
Submitted: 1 year ago.
Category: HVAC
Expert:  Kcrand36 replied 1 year ago.

Hi Otis, I am Kevin, one of the tech's here on JA.

do you still require help in wiring your thermostat?

Customer: replied 1 year ago.
I do.
Expert:  Kcrand36 replied 1 year ago.

can you tell me what thermostat you had previously, and which one you are installing.

Customer: replied 1 year ago.
The original didn't have a name on it and the one I bought is a honeywell rth3100c
Expert:  Kcrand36 replied 1 year ago.

do you have heat pump? Electric heat backup?

Customer: replied 1 year ago.
K heat pump with em.heat
Expert:  Kcrand36 replied 1 year ago.

I'm sorry, I got called out on a call.. I will open this up for other technicians to jump in and help you out. They will be able to read all conversation, just hang in there for the next available tech.

Expert:  airheatman replied 1 year ago.

Tell me what wires went to what terminals on your old thermostat

Customer: replied 1 year ago.
That's part of the problem I've installed the new thermostat , thought I did it correctly but I have two red wires but the diagram only shows were to put one
Expert:  airheatman replied 1 year ago.

OK it is always a good idea to write down or take a pic before removing but too late for that now.We are going to have to do a little investigating so see what the wires connect to on other end or you will fry the transformer in air handler.

1.I need you to go to air handler and tell me what these wires connect to. If you can take a picture, I can probably help you figure this out.

Customer: replied 1 year ago.
Here you go.
Expert:  airheatman replied 1 year ago.

Need to see where they go n air handler.

Customer: replied 1 year ago.
How do I show you that
Expert:  airheatman replied 1 year ago.

Remove panel on air handler, find the other end of these wires and take a pic so I can see what each connects to.

Customer: replied 1 year ago.
Okay getting a driver
Expert:  airheatman replied 1 year ago.

Take your time

Customer: replied 1 year ago.
There are two white wires that aren't connected and an orange wire that is not connected.
Customer: replied 1 year ago.
a green
Expert:  airheatman replied 1 year ago.

Let me look this over.Sure I will have some questions

Customer: replied 1 year ago.
Sorry it's three white wires, one orange and one green not connected.
Expert:  airheatman replied 1 year ago.

You have a mess here. I have no idea what red is what or what white is what. I can tell you what wires should go where at thermostat , air handler and outdoor if you can figure out what is what.

For example ( Red from air handler and red from outdoor to R at thermostat. Blue from air handler and blue in outdoor and C at thermostat, Green from air handler to G at thermostat,etc).

Customer: replied 1 year ago.
I'm willing to try.
Expert:  airheatman replied 1 year ago.

Give me a few minutes to type

Customer: replied 1 year ago.
Okay, thx
Expert:  airheatman replied 1 year ago.

OK the air handler should have the following control wires from factory:

Red,Green,White(possibly a brown) and Blue.

( Red is power,green is fan,white and brown if you have one is heat kit and blue is common.)

Outdoor unit should have the following:

Blue, White,Orange,Yellow and Red

(Blue is common,White sends signal to heat kit in defrost mode,Orange controls reversing valve,Yellow controls contactors and Red is power.

So heter is what we want:

1. A wire from R at thermostat to RED in air handler and RED in outdoor unit

2.A wire from C at thermostat to BLUE in air handler and BLUE in outdoor unit

3.A wire from O at thermostat directly to ORANGE in outdoor unit

4.A wire from Y at thermostat directly to Yellow in outdoor unit

5.A wire from Aux at thermostat to white, brown if you have one in air handler and white in outdoor unit

6. A jumper at thermostat from E to Aux

7.A wire from G at thermostat to GREEN in air handler.

Now with this stated it makes no difference what color wires you have ran in between the units as field installed as long as they connect to these wires in units.

Let me know if you are able to decipher this and any questions you have.

Since I see you have two reds and 2 whites at thermostat you are going to have to figure which is which in order to know where to put them.

The best thing to do is to run new wires between units containing all of the colors named, but it is possible to use what we have