No power to thermostat - what's wrong?

Question

I have a pair of 10 year old Ruud Model UPLA-024JAZ heat pumps. The thermostat for one of the units stopped working the other day. I tried switching to Heat, AC, Emergency Heat, Fan - nothing works. On my upstairs thermostat (which works) there is 24 volts between the blue and red wires but there is no voltage between blue and red or any other pair of wires on the thermostat that is not working. The heat and AC breakers were not tripped but I turned them off and on again anyway with no effect. I took the cover off the heat pump that is not getting turned on by the thermostat, and I depressed the button on top of the relay where the power cable comes into the unit and the heat pump turned on (as long as I held the button down). I thought there might be a fuse blown someplace but I cannot find one. I looked inside the blower in the garage (model UBHA-14J11NFAA) and did not find a fuse or in the heat pump on the box mounted on the side of our house by the heat pumps (it has a piece that you can slide out to discnnect power but no fuse).

Any ideas what might be wrong or where I need to look?

Thanks

Tom Esker

ransley · Accepted Answer

Bad thermostat battery, circuit breaker looks set but is in facttripped, a reset breaker on your heater unit board, get out a V meteror call a pro, im not a pro but a HO!

Speedy Jim · Answer

Each unit has its own 24V transformer.

The transformer in the non-working unit may have burned out or it has a fuse (24V side) that is open. Or the Line voltage side of the transformer is not getting power for some reason.

Locate the transformer and use voltmeter to find out.

Jim

Eric9822 · Answer

Do you have voltage where the thermostat wiring originates?  If soproblem wth field wiring.  If not problem with heat pump controller.

rfofaky · Answer

This is something you need to have a pro look at. If you checked the basics such as breaker, emergency switch, etc. and can't find anything wrong, save yourself a headache and have somebody who knows what they are doing look at it.

tesker · Answer

Thank you very much to everyone who replied. I measured 120 volts AC on the 2 wires going into the transformer but zero volts between the two wires coming out of the transformer (red and brown). Guess that confirms that the transformer is blown - unless I'm missing something.

Question: Can anyone guide me to where I can get a replacement transformer? The current one says Bassler Electric A9831 Class 2 XFMR and also BE25558001 06A and also 46-23115-82. Not sure which of these is the part number so I searched the web trying all three and did not find anything. (also tried Bassler's website with no luck). I found replacement Ruud blower transformers at

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but I have no idea which one of these I need. I know it's 24 volts on the output but I don't see anywhere on the transformer where it says how many amps (I guess that would be the other key piece of information). Any suggestions?

Also, Is it likely that something else is wrong that caused the transformer to blow? I was thinking it might be normal for it to blow on a 10 year old blower.

Thanks much

Tom Esker

EXT · Answer

Call your local Ruud dealer, and have him replace the transformer, or call to see if he will sell you one for you to install if you are capable.

Thank you very much to everyone who replied. I measured 120 volts AC on the 2 wires going into the transformer but zero volts between the two wires coming out of the transformer (red and brown). Guess that confirms that the transformer is blown - unless I'm missing something.

Question: Can anyone guide me to where I can get a replacement transformer? The current one says Bassler Electric A9831 Class 2 XFMR and also BE25558001 06A and also 46-23115-82. Not sure which of these is the part number so I searched the web trying all three and did not find anything. (also tried Bassler's website with no luck). I found replacement Ruud blower transformers at

formatting link

I have no idea which one of these I need. I know it's 24 volts on the output but I don't see anywhere on the transformer where it says how many amps (I guess that would be the other key piece of information). Any suggestions?

Also, Is it likely that something else is wrong that caused the transformer to blow? I was thinking it might be normal for it to blow on a 10 year old blower.

Thanks much

Tom Esker

Speedy Jim · Answer

> but I have no idea which one of these I need.  I know it's 24 volts on   Dirt common item at local hardware or Big Box: one that is roughly the same physical size andyou'll be good.Jim

tesker · Answer

.I found a generic transformer at a local electric supply place for$15.00 and it fixed the problem - thanks much!!

No power to thermostat - what's wrong?

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