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Old 12-13-2008, 10:34 PM   #1
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No Power to Thermostat


Okay I need to know what to do next. This morning I woke up to fine our digital thermostat does not have power. The circuit breakers check fine. I have two identical thermostats, so I changed them. After the switch in confirmed it is not a thermostat issue, so I am trying to figure out why I am not getting power. The wiring looks good at the thermostat. There are no loose wires outside at the compressor or inside in the air handler. Any ideas as to what I may do next?

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Old 12-13-2008, 11:00 PM   #2
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No Power to Thermostat


Check the transformer that feeds the thermostats. If they have battery backup the batteries are bad. Still need to fix transformers.

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Old 12-13-2008, 11:18 PM   #3
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Originally Posted by TazinCR View Post
Check the transformer that feeds the thermostats. If they have battery backup the batteries are bad. Still need to fix transformers.
Where are the transformers generally located. I did not readily see a transformer near the air handler or compressor. Does the transformer look similar to what is used for a doorbell transformer?
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Old 12-14-2008, 06:58 AM   #4
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No Power to Thermostat


It is in the air handler.
It may be good, and the low voltage fuse may have blown.
Meaning you have a short, that needs to be found and repaired.
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Old 12-14-2008, 07:07 AM   #5
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Originally Posted by beenthere View Post
It is in the air handler.
It may be good, and the low voltage fuse may have blown.
Meaning you have a short, that needs to be found and repaired.
I did see a five volt fuse in the air handler that was okay last night. Would that be the fuse to which you are referring? If that is okay then maybe I am not experiencing a short.

I guess I will pull the panel off again and find the transformer to check it out.
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Old 12-14-2008, 07:26 AM   #6
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No Power to Thermostat


That would be the fuse.
Its probably 5 amp, not volt.
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Old 12-14-2008, 04:24 PM   #7
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Originally Posted by beenthere View Post
That would be the fuse.
Its probably 5 amp, not volt.
Sorry about that yes, it is a 5 amp fuse and it is good.

I did check and both sides of the 120 and both did register 120. However the 24 volt side showed absolutely nothing.

I have a two story so I checked the other air handler and it was showing the the two 120 and the 24 volt on the other side. It does look like the transformer is at least not working.

I will have to pick one up tomorrow when there is a supply house available.

Could there be any other issues?
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Old 12-14-2008, 05:04 PM   #8
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No Power to Thermostat


Need to check what caused the transformer to burn out.
You don't want to install a new one, and watch it smoke.
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Old 12-14-2008, 07:24 PM   #9
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Need to check what caused the transformer to burn out.
You don't want to install a new one, and watch it smoke.
Exactly I do not want to install it and watch it fry, but I am at a loss as to what to check at this point.
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Old 12-14-2008, 09:51 PM   #10
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No Power to Thermostat


All teh low voltage wires for shorts, and the low voltage componets.

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