Air Conditioning - No power to thermostat.

Hello all,
Hopefully someone has run across this before and can lend a hand.

I have two goodman heat pumps: 1 ton for downstairs and 2 ton for upstairs.

Recently the thermostat upstairs went dead no power or lights. After reading in this forum a bit I determined that there was no power to the thermostat so I ordered and installed a new transformer, which was located on the heat pump outside just below the control board. I disconnected all power prior to the change. After installation of the new transformer the thermostat is still dead. I changed the thermostat with the identical one from downstairs, which I know works, and it is still dead, further the dead tstat from upstairs works fine downstairs, so I have eliminated the tstat as the problem.

I have checked all connections of the thermostat wire and all wire caps.

My question is could the problem be the control board, or perhaps a fuse I am not seeing?

Additional info: with the old transformer I could force the compressor on by manually tripping the contact points, however this did not activate the blower.

Any info would be greatly appreciated...

Sincerely, Razor :)

Check your indoor unit. You probably have 2 transformers.

Hi Mattison, thanks for the speedy reply....

You are correct, there is another transformer in the air handler itself...

I have a fluke meter, perhaps you could instruct me as to how to check the voltage on the 2nd transformer before I order a new one....

Thanks, Razor :)

Hi,

To finish this post: I went ahead and ordered a new transformer for the air handler in the attic. I shut off all power and installed the new transformer being sure to wire it correctly, powered up and now have full a/c and heat.

Thanks for all of your help...

Rgds/Razor

Good fix. Sorry I didn't catch your earlier question on how to check it.

Hi guys,

After installing a new 24 v transformer in my airhandler and also a new transformer at the heat pump outside, I ran a jumper between the R & G wire at the thermostat and the compressor, fan and blower all ran cooling the upstairs in my home. I was pretty sure that the tstat was gone because it would not light up nor would it activate the heat or ac after the new transformer was installed. I left the jumper wire on over night just to have cool air until I went to home depot in the morning. The next morning the ac unit quit again, ( no power to tstat ) and I am wondering if I burnt out the 24v transformer again....? My son went up and took pictures of the air handler wiring for me but I could not see anything amiss I/E burnt or disconnected wire.

Hopefully there isn't anything else wrong which may be burning out these transformers....

I have 2 goodman heat pumps 1 ton / downstairs and 2 ton upstairs both with its own air handler.

The existing thermostat has 6 wires R, G, W, Y, Blue, Brown



Any info is greatly appreciated....

Sincerely, & thanks in advance,
Razor

From what you say you have on the tstat you cant have two transformers. that run the system. You could have a RH power from one trans. and a RC for cool power. You only need one . 6 wires I take it you have a heatpump.
Look on the blower door should have a wire schermatic there for the unit . with the power on a cheap meter will read 24V at the trans.

Hello again,

Regretably, this seems to be an ongoing problem for us . . .

After going without air upstairs for a while, we were able to order a new 24v transformer and thermostat.

We shut down all of the breakers inside the house, and at the heat pumps outside, and in the attic as well. We installed the digital ( Rite Temp ) thermostat and the new 24v transformer in the airhandler as well. We swapped the wires one by one from the old transformer to the new.

We then reset all the breakers, switched the thermostat to cool, and set it for 70 degrees.

The AC kicked on and cooled the upstairs for the next 2 days and . . . again now no AC....

The blower is not running and the heat pump fan is not spinning.

I guess the next question is what might be causing these transformers to blow ?

Is there another component in the air handler or heat pump itself that may be the culprit?

System Info:

2 goodman heat pumps outside 1 ton for downstairs and 1.5 for upstairs.

Both pull double duty heating and cooling each floor.

I did replace the contactor in the heat pump for upstairs, as well as replaced the 24v transformer twice. The large capacitors in both heat pumps were replaced as well.

I apologize if I havent given enough information, this is not my area of expertise, however, I can post pictures if necessary.

Any insight would be greatly appreciated....

Sincerely,
Razor

Hello again,

I just wanted to add that the new tstat has a jumper between rh and rc. All of the other wires are connected to their respective posts. Y to yellow, W to white, Green to G, Blue to B, Red to RC, and the last wire is a light brown connected to O.

The old thermostat was a mercury one and had only an R terminal not Rh and RC.

I hope that helps...

Thanks again...

Razor.....

You have a heat pump? Reason I ask is that you said O wire...

Hi Jay,

Yes, I have two heat pumps the larger one is for the upstairs that is not working. The O wire was connected to the O terminal on the old mercury thermostat, so I attached the O ( brown wire ) to the O terminal on the new thermostat.

I should have a fluke meter here later today to check the 24v at the thermostat. I would also like to install an inline 5 amp fuse on the transformer if it is still good or on a new one, however I do not know which wire to install it on or on which side of the transformer to do it.

I have enclosed this picture of the transformer

http://img.photobucket.com/albums/1003/straightrazor/STUFF/transformer.jpg

I hope that is what you meant, and thanks for the reply...

Thanks, Razor

Hello All,

Here is a better picture of the transformer. The specs are more easily read.

http://img.photobucket.com/albums/1003/straightrazor/STUFF/TRANSFORMER2.jpg

I have jumped the r & g wires at the tstat with no result so evidently there is no power getting there. Thats about all I can do until I get the fluke meter here.

Thanks for all of your assistance....

Sincerely, Razor

Hello Again,

After reading many posts here, we went out to Frys and purchased a:

50VA Multi-Mount, Multi-Tap Fuse Protected Transformer
Primary 120/208/240VAC/24VAC Out
UET150

This would bring our transformer from 40va to 50 va and it would be fuse protected as well.

Here is a picture of the new transformer

http://img.photobucket.com/albums/1003/straightrazor/STUFF/product_controlTransformer.jpg

It has two 24v screw terminals on the front below the fuse and 4 wires coming from the back: Black, White, Red, and Tan.

Here is a picture of the old transformer and wiring

http://img.photobucket.com/albums/1003/straightrazor/STUFF/TRANSFORMER2.jpg

If someone could tell me how to wire the old to the new It would be greatly appreciated.

Thanks in advance for your assistance....

Sincerely, Razor

Not enough information---The wire colors of the new transformer really don't tell me anything. Look at the instructions (of the new transformer) and use the wires designated for 240 volt operation.

It sounds like you have an intermittent short somewhere in your low voltage wiring. It could even be a bad contactor coil pulling too many amps. You need to carefully check all this wiring. A common place for low voltage shorts is at the condensing unit. Frequently, the insulation breaks down or is damaged by weed eaters or animals.

Hello Jim,

Thanks for the reply.

Part of the problem is that the new thermostat didn't come with directions. I have done an exhaustive search on the internet and found nothing including at the manufacturers website. I have written to them for instructions.

I will check at the heat pump for shorts i/e weed wacker damage etc.

I did make a wiring atempt on the new thermostat based upon advice from " someone knowledgable ". I removed the thermostat face plate as a safety measure and when I threw the breaker there was a small pop in the air handler. The 5a fuse did not blow, but obviously the wiring was not correct.

Now I'm wondering what else may have been fried...

It may be time to call someone in, as much as I hate to do that, it may be necessary...

Thanks, Razor

Thanks to everyone for all of your assistance and replies.

We went to Frys and purchased a 24v transformer that had 3 wires coming from the primary ( white, red, and orange ) and two 24v screw terminals on the secondary.

Based upon the rating stamp on the bottom, the orange wire was for the 240v application I needed and the white had a neutral value. We wired it that way and put a 5 amp inline fuse on each 24v secondary terminal.

Ac is blowing cold , thermostat acting fine and for now at least all is well :)

Thanks again all for your help..

Sincerely, Razor