I need to replace the transformer on my A/C unit (according to the tec).
The replacement looks like this: http://i236.photobucket.com/albums/ff260/wrager46/th_transformer.jpg (http://s236.photobucket.com/albums/ff260/wrager46/?action=view&current=transformer.jpg)

It has two screw terminals for the secondary side. The orginal version has a yellow and red wire that are hard wired. How do I know which color goes to the individual screw terminals?

I need to replace the transformer on my A/C unit (according to the tec).
The replacement looks like this: http://i236.photobucket.com/albums/ff260/wrager46/th_transformer.jpg (http://s236.photobucket.com/albums/ff260/wrager46/?action=view&current=transformer.jpg)

It has two screw terminals for the secondary side. The orginal version has a yellow and red wire that are hard wired. How do I know which color goes to the individual screw terminals?

It doesn't matter. It's AC. Now with all due respect, if you don't know that I would not be poking around inside an HVAC system. For example is the primary voltage 120 or 240v? It's probably 120 but I have an air handler in my HT that is 240v. Also why is the transformer bad? They do fail on their own but there could also be a short on the low voltage system as well. If there is you are just going to destroy the new transformer.

Thanks for the help Glimmie! The only reason I am attempting this is because the service tech diagnosed it ($85) and said the control board and transformer needed to be replaced ($525). I got the new board and transformer for under $200. The board was easy (flip breaker off) , just pull wires from one board, put on new board. The transformer was not exact 1:1 replacement, so that's where I stopped.

I wouldn't try any other repairs, but these two seemed very straight forward. It is 120v primary according to the old transformer.

logically if the take off screws aren't marked in any way then it doesn't make any difference how you hook up the wires.

If it made a difference then they would be marked so you could tell which is which. This advice is worth what I charged and I am not responsible for any damages that may result from following it.

This advice is worth what I charged and I am not responsible for any damages that may result from following it.

hey Big... you mind if i make that apart of my sig...?

Hey BIG, I kind of came to that same conclusion. I appreciate your thoughts. No worries about advice taken...I'm "not that guy."

It's interesting...we (theater DIYers) do all sorts of crazy things that most mortels would never do (like hanging an 180 lb CRT from the ceiling with a dry wall lift), yet delving into HVAC stuff seems crazy. I realize we need to take precautions, but hey, I can read a wiring diagram.

Wiring diagram? In Acworth! Come on.

Dennis! You are too funny!
I credit you with my amazing theater...because of your contributions to this site.

hey Big... you mind if i make that apart of my sig...?
take it, but I reserve the right to claim intellectual property rights at any time in the future.

The only thing that concerns me about the transformer is that I was under the impression the yellow wire was some sort of "standard" (I use that loosely here) for the control wire to an external compressor.

Are you sure there isn't any marking next to either of the screws, like a "Y" or something.

The job of a low voltage transformer is to take 110 volts AC on the primary end, and transform or lower the voltage to 24 volts on the secondary end. That is why on the transformer label, below it has "PRI" 120, 208, 240 and SEC 24V 40VA. The transformer that we sell can be used with multiple voltages either 120 volts, 208 volts or 240 volts. You would hook up the right color coded wire to use the voltage that you have. The color coded voltage wiring directions are on top of the transformer. For example: The white and black wires would be used for 120 volts for most furnaces. The White and Orange wire would be hooked up if you were using the transformer to replace a bad transformer on an outdoor air conditioner or heat pump that uses 240 volts. The Blue & Yellow wire are the secondary 24 volts AC.

http://www.arnoldservice.com/air_conditioning_parts.htm

The job of a low voltage transformer is to take 110 volts AC on the primary end, and transform or lower the voltage to 24 volts on the secondary end. That is why on the transformer label, below it has "PRI" 120, 208, 240 and SEC 24V 40VA. The transformer that we sell can be used with multiple voltages either 120 volts, 208 volts or 240 volts. You would hook up the right color coded wire to use the voltage that you have. The color coded voltage wiring directions are on top of the transformer. For example: The white and black wires would be used for 120 volts for most furnaces. The White and Orange wire would be hooked up if you were using the transformer to replace a bad transformer on an outdoor air conditioner or heat pump that uses 240 volts. The Blue & Yellow wire are the secondary 24 volts AC.

http://www.arnoldservice.com/air_conditioning_parts.htm

This is typical for standard 40va HVAC transformers. But the sample shown is not that type. It looks to be a 120v only unit.

To the OP: Just make sure you don't get the primary and secondary mixed up. That would be quite damaging as well as dangerous.

The only thing that concerns me about the transformer is that I was under the impression the yellow wire was some sort of "standard" (I use that loosely here) for the control wire to an external compressor.

Are you sure there isn't any marking next to either of the screws, like a "Y" or something.

I think you are refering to thermostat wiring. Yesthere is a standard for that. But a transformer secondary has no polarity (well it does, but not relevant in this case). It doesn't matter which way the secondary is wired.

Wow...thanks. You guys have been tremendously helpful. The primary is well identified and a one to one replacement so no issue there.

Thank you, thank you! It's fixed and working now! You guys helped me save $300!

In Georgia ...

All distances (speaker distance, how long to cut the 2x4, distance to Bubba's still, width of door) are always: 'bout, yea'

The common answer by a contractor to a difficult problem, or show stopper (example: screen too big for projector's throw distance, speaker won't fit in cabinet, ceiling height too low in basement, 6" of water on basement floor): 'nah, t'aint nutten, we's got that ol' sledge in the pickem up'