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Old 01-11-2011, 06:49 PM   #1
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Testing transformer


Friends blower stopped working. Checked his thermostat and hot red wire was dead. Checked his unit in attic. Blower motor humming bad not spinning and hot. Capacitor checked ok. But this kind of threw me. Looks like a combo transformer and fan relay tied together. Red 24v wire on front is dead. So I'm to assume transformer is dead but was confused because fan was trying to run, reading a dead transformer and thermostat was in off position. Am I reading this transformer wrong and just dealing with a bad fan motor or is it a combo of things happening here. Any feedback is greatly appreciated.
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Old 01-11-2011, 07:53 PM   #2
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Testing transformer


Blower motor humming bad not spinning and hot.

I am not the expert here. But don't try to read too much into this. Blower motors do fail. They aren't that expensive or too much trouble to replace. It humming and being hot should tell you alot. Probably all you really need to know. Shut it down before you have worse problems. Like a fire!
Just my 2 cents worth.

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Old 01-11-2011, 07:58 PM   #3
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Testing transformer


fan relay may be stuck? Transformer may be shot?
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Old 01-11-2011, 08:33 PM   #4
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Testing transformer


The transformer is on these units to lower the (24 volts) voltage to a safer level because of fingers touching the thermostat. Don't want 120 volts in the wrong hands.
If the fan motor is trying to start then the transformer should be doing its job, which is supplying (control only) voltage to the T-Stat.
Sounds like the fan bearings are bad. With the power off can you spin the fan? Does it continue to spin freely for a few seconds?
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Old 01-11-2011, 09:16 PM   #5
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Testing transformer


Quote:
Originally Posted by hvactech126
fan relay may be stuck? Transformer may be shot?
Thanks for the info. Looks like their is a generic relay/transformer I can replace with about $25. Motor easily accessible as well. Thanks again for info.
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Old 01-11-2011, 09:22 PM   #6
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Testing transformer


Quote:
Originally Posted by Know It ALL
The transformer is on these units to lower the (24 volts) voltage to a safer level because of fingers touching the thermostat. Don't want 120 volts in the wrong hands.
If the fan motor is trying to start then the transformer should be doing its job, which is supplying (control only) voltage to the T-Stat.
Sounds like the fan bearings are bad. With the power off can you spin the fan? Does it continue to spin freely for a few seconds?
I did try and spin it and it dont think it spun that well.

I just ran my voltage detector over wire connections at transformer and it read zero. Also zero at thermostat so thought transformer was bad but confused when I saw a two part transformer. Then saw that it was some sort of fan relay built in. Just wanted to double check any other things I should test befor I replace both
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Old 01-11-2011, 11:27 PM   #7
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Testing transformer


24v between r and c. use a meter not noncontact voltage
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Old 01-13-2011, 08:48 AM   #8
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Testing transformer


Quote:
Originally Posted by hvactech126
24v between r and c. use a meter not noncontact voltage
Thank you for all the input. Looks like it was just the blower motor. Transformer and fan relay seem to be working fine now. Whew! Heat again.

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