View Full Version : 24v transformer rewiring.

08-15-2007, 02:19 AM
:) Hello All,

Im new here and would like to ask a question. I'm hoping it is in the right place here.

I am trying to wire in a new 24v transformer into my airhandler.

Here is a picture of the old 24v transformer which is fried.


The replacement is a :

50VA Transformer
120/208/240VAC/24VAC Out

Here is a picture of the replacement:


The new transformer is fuse protected as you can see, and has 4 wires coming out of the back, Black, White, Red, and Tan.

This is to power the thermostat for the Air Conditioner, so for now no ac....

If more info is needed please let me know....

Any assistance is greatly appreaciated

Sincerely, dmlf57

08-15-2007, 02:44 AM
What is your question?

08-15-2007, 03:08 AM
do u want to wire the transformer or simply connect it?

08-15-2007, 03:56 PM
:) Hi All,

Thanks for the replies,

I guess what I am asking is that the new transformer has 4 wires coming out of the back and I am unsure as to which one would use to have it function with 240 volts. It should be 240 in the back to 24vac in the front on the screws. With 4 wires, ( and it didnt come with instructions ), I am unsure as to which to use.

I thought maybe someone here may have seen this before.

Thanks in advance for your help....

Sincerely, dmlf57

08-15-2007, 03:58 PM

Hi again,

In the first picture, of the old transformer, there is a red wire on the top right and a black wire on the top left, both of those have to be connected to 2 of the four wires on the back of the new transformer. The bottom two wires on the old transformer, I believe, go to the screw terminals as 24vac on the front of the new transformer. I hope that helps...

Rgds, dmlf57

08-15-2007, 05:11 PM
the replacement model looks very much like the type that mounts to an electrical box by the flanges, which when doing so will confine the higher voltage connections (208 or 240 vac in your case) inside the box, and leave the 24 vac connections outside the box. they usually come with a special box cover that accepts those flanges. hth

08-15-2007, 05:37 PM
i really m clueless about this one.
hope some1 has worked with these kinds here who can help u.

btw it wud be easy too determine the wires if u can conduct a open cicuit test on the transformer using a autotransformer or dimmerstat.
for safety sake keep the voltage below 24 volts even if conducting on high voltage side. (a couple of days ago i fried a smps and capacitor dielectric came out with explosion )

P.S -for some reason i cud not see the image in my mozilla ff , anybody else
experiencing similar problems?

08-15-2007, 07:20 PM
Each wire is a lead to the transformer primary. The wires are color coded to the different voltages (neutral, 120, 208, 240). I could guess on the color code, but I'm not sure. The screw terminals are the 24V secondary.

08-15-2007, 11:03 PM
I found that model number here but the link on their page is borked. This is a direct link to it. Eh, Icanhasfooskillz?
And UEI's

Bah, worthless crap.
Does the label on top have the color codes?

08-17-2007, 04:56 PM

Thank you everyone for your efforts and replies, they are very much appreciated.

Cb83's post about each wire on the primary handling a different voltage began to make sense to me then it all came together.

Please look at the picture below . . .


This is a replacement transformer I bought at Fry's yesterday which has 3 wires coming from the primary, White, Red, & Orange.

Based upon the rating stamped on the bottom, and cb83's post I was able to reason out that the orange wire handled the 240 volts which I needed and the white wire had a neutral value.

We wired it that way and placed 5 amp in-line fuses on the 24v side to protect the transformer.

Now the AC upstairs blows cold air like in a bowling alley :)

Thanks again for all of your help.... You guys ROCK :)

Sincerely, dmlf57