Thermostat wiring on A/C unit

[R Bob]

You are correct. color does not matter, but in A.C. only......Y at the t-stat,or relay goes to the compressor, R (RC for cooling)is hot, RH is heat (isolated at the sub-base to prevent any bucking) W is common, B is common, but used in heat pump rev. valves, G is fan.

Never had any electrician do my control wiring....

It has been my experience that:

For the sake of simplicity, color does matter...that's why there are different colored wires. (Technically, color doesn't matter as long as all of the terminations are correct.)

"R" is power/control power source. "RC"=power/cooling and "RH"=power/heating.
"RC" and "RH" are, in fact, isolated @the sub-base to prevent bucking of 2 different power sources.
If there is only 1 control power source(which is typically the case), "RC" and "RH" on the T-Stat are jumpered.

"W" is typically a call for heat...not common, even though it may be switched through common.

"Blu" is typically common/control power source.

"B" and "O" are typically used for the reversing valve on a heat pump. Which one you use depends on the mfgr. One energizes the reversing valve in the heating mode and the other energizes the reversing valve in the cooling mode.

"G"=fan.

 

[LarryFine]

In case you're wondering, the colors come from the evolution of HVAC. 2-conductor T-stat wire is red and white for heat, whether 24v or micro-volt (thermo-couple generator); 3-c is red, white, plus green for the fan, because forced-air blowers came next; 4-c adds the yellow for the A/C when it came out; and so forth.

 

[jaylectricity]

In a cooling only setup you only need two wires to the condensor and two or three to the thermostat. I can't say which ones or which way to connect them without seeing the setup.

On a side note. Why do guys around here let the HVAC guys do this wiring?

Aren't we the electricians? Don't we do wiring?

I hear this from guys all the time. Both electricians and HVAC guys. I don't get it. I always do all of the wiring on an HVAC system.

Yeah, I figured out three to the thermostat...I ran five, just in case they add heat to that air handler someday.

But yeah, it's kind of why I asked the question...I want to do the wiring every time now. I used to be happy passing it off to whoever was willing to do it.

Funny thing, while talking to the customer today he conveyed his belief that he'd rather have a licensed electrician do all electrical wiring in his house because: "They are electricians!"

From now on I will make it a point to learn this stuff...maybe take a class for my continued education requirement.

 

[jaylectricity]

Ok, first off...celtic: I don't see an address to send you anything...so...NO SOUP FOR YOU! or baked goods as we may.

Second of all...concerning the colors...Thermostats are fairly simple. The terminals are labeled R, G, Y, B, W and your typical 18/5 is Red, Green, Yellow, Blue, White...

So why are the air handler wires colored in such random fashion? Usually the red is red, but in this particular case, the blue wire coming out of the handler was the secondary wire off the transformer to complete the circuit on the condenser. So I have a red and white wire to my compressor and I had to hook the yellow wire from the Tstat to the red wire to the condenser and the the blue wire from the air handler to the white wire to the compressor.

To make it worse, the leads in the compressor were blue and yellow.

Is there an 18/2 cable that has a blue and yellow conductor? Because that would help a LOT!

 

[hurk27]

On a side note. Why do guys around here let the HVAC guys do this wiring?

Aren't we the electricians? Don't we do wiring?

I hear this from guys all the time. Both electricians and HVAC guys. I don't get it. I always do all of the wiring on an HVAC system.

Because many of us have liability insurance that only covers us doing electrical building type work.

If an appliance has water or Gas ran to it, it's off limits to us to hook up gas, water, or controls, as if something was to happen, our insurance would not cover it. HV (120/240v) supply to it, and that is as far as it goes.

 

[quogueelectric]

I learned the color code in 85 as white heat ist stage/ red common/yellow cooling ist stage /green fan has served me well for for 24 yrs.

 

[celtic]

Ok, first off...celtic: I don't see an address to send you anything...so...NO SOUP FOR YOU! or baked goods as we may.

Just PM me your CC info ~ I'll handle the rest.

 

[electricmanscott]

Because many of us have liability insurance that only covers us doing electrical building type work.

If an appliance has water or Gas ran to it, it's off limits to us to hook up gas, water, or controls, as if something was to happen, our insurance would not cover it. HV (120/240v) supply to it, and that is as far as it goes.

I find that very hard to beleive.

What do gas and water have to do with anything here?

 

[iwire]

Because many of us have liability insurance that only covers us doing electrical building type work.

If an appliance has water or Gas ran to it, it's off limits to us to hook up gas, water, or controls, as if something was to happen, our insurance would not cover it. HV (120/240v) supply to it, and that is as far as it goes.

Uh, I am an electrician, I can, and do wire controls.

 

[hurk27]

Uh, I am an electrician, I can, and do wire controls.

Yea I know it sounds dumb, but back a few years ago, we had one of our guys, miss wire the controls to a furnace, and some how caused the gas burner to fire continually and did some damage, and the insurance adjuster pointed out a clause in the policy stating something like " it does not cover the internal control wiring to a furnace without a HVAC certification" we are allowed to run the T-stat wiring, but can't do the final connection to a furnace with out being under the supervision of a certified HVAC person.:roll: