# HVAC transformer wiring question



## nap (Dec 4, 2007)

what do you mean by "out"


in a 24v transformer where neither terminal is grounded the terminals outputs are interchangeable.


----------



## user_12345a (Nov 23, 2014)

Some circuit boards may be picky about polarity. In theory it shouldn't make a difference, as it's ac.

The transformer may have a little schematic on it to tell you which side is hot vs neutral.


----------



## zappa (Nov 25, 2011)

What is your common in? There shouldn't be one unless you are talking about the ground wire. Take your pick on the 24 volt output as it doesn't make a difference.


----------



## nap (Dec 4, 2007)

user_12345a said:


> Some circuit boards may be picky about polarity. In theory it shouldn't make a difference, as it's ac.
> 
> The transformer may have a little schematic on it to tell you which side is hot vs neutral.


there is no neutral on the secondary of a 24vac transformer.

and a neutral is not the same thing as a grounded conductor although most people believe they are. Not all grounded conductors are neutrals and not all neutrals are grounded conductors.


----------



## xcom (Jul 28, 2015)

nap said:


> what do you mean by "out"
> 
> 
> in a 24v transformer where neither terminal is grounded the terminals outputs are interchangeable.


Thanks. This is exactly what I was looking for.


----------



## user_12345a (Nov 23, 2014)

nap said:


> there is no neutral on the secondary of a 24vac transformer.
> 
> and a neutral is not the same thing as a grounded conductor although most people believe they are. Not all grounded conductors are neutrals and not all neutrals are grounded conductors.


All I know is that there's a load side and a secondary side, that at least on some modern furnaces is tied with ground.

Neutral is the wrong term i guess.


----------



## nap (Dec 4, 2007)

user_12345a said:


> All I know is that there's a load side and a secondary side, that at least on some modern furnaces is tied with ground.
> 
> Neutral is the wrong term i guess.


yes, neutral would be the wrong term

additionally using "load side" and "secondary side" would also be incongruent.


you can have a primary and secondary side _or _a line and load but a load side and a secondary side are one and the same.

unless the transformer in hand has a bond to the frame from either of the terminals which terminal is grounded is irrelevant/ I cannot say I have run across a transformer with an integral ground yet.


----------



## Bob Sanders (Nov 10, 2013)

xcom said:


> My transformer has 2 OUT (yellow and blue) cables. But on my old Transformer the colors are black and red. any advice?


Doesn't make any difference which one you use for the "R" and "C". The secondary (24volt) side is isolated from the primary side. There is no "hot" or "Neutral", Positive, or negative. Just make sure that once you pick one as the "C" wire, it stays the common wire throughout your design.


----------



## xcom (Jul 28, 2015)

Bob Sanders said:


> Doesn't make any difference which one you use for the "R" and "C". The secondary (24volt) side is isolated from the primary side. There is no "hot" or "Neutral", Positive, or negative. Just make sure that once you pick one as the "C" wire, it stays the common wire throughout your design.


The two 24v wires go down to the thermostat R and C? yes/no?

If yes, does it matter if they are swapped on the thermostat? If I have my R on the C and my C on the R for example. Or the only important thing is that they don't cross.


----------



## zappa (Nov 25, 2011)

xcom said:


> The two 24v wires go down to the thermostat R and C? yes/no?
> 
> If yes, does it matter if they are swapped on the thermostat? If I have my R on the C and my C on the R for example. Or the only important thing is that they don't cross.


Yes, R and C.

You can't swap them at the thermostat. R has to stay on R because the thermostat switches that signal.


----------



## xcom (Jul 28, 2015)

zappa said:


> Yes, R and C.
> 
> You can't swap them at the thermostat. R has to stay on R because the thermostat switches that signal.


well that might be a problem. How does R and C normally traverse the circuit board. How can I identify one over the other. I'm using pre-existing wiring with different color coding.


----------



## zappa (Nov 25, 2011)

xcom said:


> well that might be a problem. How does R and C normally traverse the circuit board. How can I identify one over the other. I'm using pre-existing wiring with different color coding.


Maybe I'm not understanding what you are doing. Are you just replacing a bad transformer?

Take the old one out and wire in the new one. The two 24 volt wires coming out of the transformer have no polarity so it doesn't matter which one gets connected to R and which one is connected to C.


----------



## xcom (Jul 28, 2015)

zappa said:


> Maybe I'm not understanding what you are doing. Are you just replacing a bad transformer?
> 
> Take the old one out and wire in the new one. The two 24 volt wires coming out of the transformer have no polarity so it doesn't matter which one gets connected to R and which one is connected to C.


sorry I thought someone was implying on the thermostat side the R and C were connected to the same R and C on the transformer. I misunderstood. I think it's cleared up for me. really appreciate everyones help


----------



## zappa (Nov 25, 2011)

xcom said:


> sorry I thought someone was implying on the thermostat side the R and C were connected to the same R and C on the transformer. I misunderstood. I think it's cleared up for me. really appreciate everyones help


Well yes, they usually are. They are also connected to other things inside of the unit which means that you can't go to the thermostat and switch R and C around. C is also grounded to the chassis in many cases.

Don't overthink this. The transformer output wires have no names until it gets hooked to R and C which means you can't hook it up wrong.


----------



## zappa (Nov 25, 2011)

You never answered my question about why you are changing the transformer. Let me add that they are usually pretty reliable and don't often fail for no reason. It's possible that your unit has a problem and could take out the new transformer as well.


----------



## xcom (Jul 28, 2015)

zappa said:


> You never answered my question about why you are changing the transformer. Let me add that they are usually pretty reliable and don't often fail for no reason. It's possible that your unit has a problem and could take out the new transformer as well.


I was trying to change out the thermostat and I crossed the blue and red wires. The HVAC guy said I blew the transformer. I bought a new one and it didn't fix the problem. Thankfully it's only $22 bucks. It ended up being a tiny fuse that I blew when I crossed the wires. I replaced the fuse and I'm getting 24v at the thermostat on the red wire.

Here's my problem now.

When I test... I hookup the red wire with the green and my fan turns out. great I have air coming out of the vents. I include the yellow wire and the heat pump outside turns on (I hope I'm saying this right). I can hear the compressor kick in for a few min then it sounds like a hissing noise and shuts off. It continues on this short cycle of turning on and off. I feel the valves and they are warm coming in AND out from the heat pump. I thought one would be cold and the other hold with the AC on.

I tested the capacitor and the delay fuses at the heat pump and both were in good shape. I'm a bit worried but I've done a lot to troubleshoot. any tips or suggestions? I can take pictures of all my equipment and model numbers if it helps. I can also take images of the wiring inside the carrier box in the attic.


----------



## xcom (Jul 28, 2015)

Forgot to add. Yellow, green, red result in hot air /heat


----------



## zappa (Nov 25, 2011)

xcom said:


> Forgot to add. Yellow, green, red result in hot air /heat


1) Was there any problems with the cooling before you shorted the wires?
2) Are you jumping wires wires together to make it run or using a thermostat?
3) Is it hot at your location?

Most heat pumps need the reversing valve (O) energized to put it in cool mode. If you run it in "heat mode" in summer temperatures the head pressure sky rockets. The hissing may be the pressure bypass or it's shutting down on high head pressure.


----------



## xcom (Jul 28, 2015)

zappa said:


> 1) Was there any problems with the cooling before you shorted the wires?.


 No. We had just bought the house and was demolishing and repainting so I took everything off the walls not thinking to take pictures of the wiring on the thermostat. now I'm not sure how they all go back.



zappa said:


> 2) Are you jumping wires wires together to make it run or using a thermostat?


 Yes, I'm jumping wires together (no thermostat). I Figured until I can confirm it's working properly I won't involve the thermostat.



zappa said:


> 3) Is it hot at your location?


 Yes I live in California




zappa said:


> Most heat pumps need the reversing valve (O) energized to put it in cool mode. If you run it in "heat mode" in summer temperatures the head pressure sky rockets. The hissing may be the pressure bypass or it's shutting down on high head pressure.


What color would the reversing valve be? I have red,blue,yellow,green and white.


----------



## zappa (Nov 25, 2011)

Probably the blue wire...


----------



## xcom (Jul 28, 2015)

zappa said:


> Probably the blue wire...


ok. so my next test will be red+green+yellow+blue. stay tuned for my results


----------



## xcom (Jul 28, 2015)

xcom said:


> ok. so my next test will be red+green+yellow+blue. stay tuned for my results


test was a success. RGYB has cold air coming out. Would you happen to know why when I connect red and white my fuse blows every time?


----------



## Bob Sanders (Nov 10, 2013)

xcom said:


> Would you happen to know why when I connect red and white my fuse blows every time?


White is probably your C wire.

You're shorting out the transformer. Don't do that. R and C are not meant to be connected directly together without some kind of load between them.


----------



## zappa (Nov 25, 2011)

White is normally auxiliary heat and there may be something wrong with the circuit. It's also possible that it is being used as common (C) which would explain the short circuit. Does your thermostat run on batteries? If not, it must be the common.


----------



## xcom (Jul 28, 2015)

zappa said:


> White is normally auxiliary heat and there may be something wrong with the circuit. It's also possible that it is being used as common (C) which would explain the short circuit. Does your thermostat run on batteries? If not, it must be the common.


the old thermostat is "NOT" run on batteries. My new one does.


----------



## zappa (Nov 25, 2011)

xcom said:


> the old thermostat is "NOT" run on batteries. My new one does.


Do you want the new one to run on batteries? The white is common and can power thermostats so you might have the option not to use batteries depending on the new stat.


----------



## Bob Sanders (Nov 10, 2013)

zappa said:


> White is normally auxiliary heat and there may be something wrong with the circuit. It's also possible that it is being used as common (C) which would explain the short circuit. Does your thermostat run on batteries? If not, it must be the common.


I'm not sure we should be folowing color schemes here.

In one statement he says

"test was a success. RG*Y*B has *cold* air coming out."

and in another one he says:

"Forgot to add. *Yellow*, green, red result in *hot air /heat*"

Is it possible for you (OP) to give us a picture of the thermostat connections along with the air handler and heat pump connections?

We could clear this up pretty fast with some good pictures.


----------



## xcom (Jul 28, 2015)

I took a picture of my new thermostat. it's battery operated. Any help with wiring it up would be greatly appreciated. I have a couple jumpers too just incase.


----------



## zappa (Nov 25, 2011)

Bob Sanders said:


> I'm not sure we should be folowing color schemes here.
> 
> In one statement he says
> 
> ...



His colors are just fine Bob. He didn't have the reversing valve energized.


----------



## xcom (Jul 28, 2015)

Bob Sanders said:


> I'm not sure we should be folowing color schemes here.
> 
> In one statement he says
> "test was a success. RG*Y*B has *cold* air coming out."
> ...


 

With RG - only fan
With RGY- fan + hot air
With RGYB- fan + cold air
With RW - blown fuse

I thought W was heat so I connected it to Red. that's how I blew that fuse the first time around. But my old thermostat was not battery operated so it would make sense that W in this case is the common.


----------



## xcom (Jul 28, 2015)

Now that I know W is common plugging W into "W" of the thermostat would be a big no no........ 

As far as wiring. I believe I'm understanding this to be.

Blue wire - "O" terminal
Red wire - "R" Terminal with a jumper into Rc
Yellow Wire - "Y" Terminal
Green wire - "G" Terminal
White Wire - No terminal. Cover with electrical tape.

Is that accurate?


----------



## zappa (Nov 25, 2011)

> Is that accurate?


Yes...


----------



## yuri (Nov 29, 2008)

W on the thermostat is always for a gas furnace. If you have elec strip heaters and a air handler then the wiring may be different.

Post the brand and model # of the air handler and heat pump and whether it has strip heaters. A pic of the terminal strip and control board of it also helps.


----------



## xcom (Jul 28, 2015)

I want to take a moment to thank everyone who posted in this thread. you're all the hero's in my book. My AC is now fully functional and the new thermostat in place. Being a new home owner this is yet "Another" lesson I've learned in life. The first one was throwing out old doors without using them to template the new doors. Good lord that was interesting.


----------



## zappa (Nov 25, 2011)

You're welcome. Thanks for keeping us posted with the outcomes and not just disappearing.


----------



## xcom (Jul 28, 2015)

*heat never tested*

NP Zappa. So the summer was great. AC was working like a champ. Now it's getting a bit colder and I'm realizing that the heat never worked since the cold was fixed. I attached an image of my connections.When I hookup the white wire to the "W/aux" it blows the small fuse. When I put a volt meter to the white wire and touch yellow I don't get 24v. (I was curious if it had current running across it, "it does not"). I'm pretty sure the blue wire is the heat pump reversing valve or the cold would not have worked all this time. thoughts?



zappa said:


> You're welcome. Thanks for keeping us posted with the outcomes and not just disappearing.


----------



## beenthere (Oct 11, 2008)

Disconnect the blue wire from the O terminal, and see if you get heat. if so, either the thermostat is not set up properly, or its defective.


----------



## xcom (Jul 28, 2015)

beenthere said:


> Disconnect the blue wire from the O terminal, and see if you get heat. if so, either the thermostat is not set up properly, or its defective.


Blower is active but the heat pump is not on.


----------



## xcom (Jul 28, 2015)

It's possible I have it configured incorrectly. Trying to understand if I should be set to 0 or 1.

* Function 1: System Type​ 0 Heating & cooling:​* Gas, oil or electric heating with​
central air conditioning or heat pump without auxiliary/​ back-up heat.​* 1 Heat pump with auxiliary/backup heat:​* Outside​ 
compressor provides both heating and cooling.

==============

*update*

changed function 1 to "1" for heat pump

Also changed my heating cycle rate from oil/gas to electric. Don't know how I missed that in the original setup.


----------



## xcom (Jul 28, 2015)

heat and cool works now. thank you!


----------



## beenthere (Oct 11, 2008)

Your welcome.


----------



## roughneck (Nov 28, 2014)

Is this a heat pump?


----------

