blown transformer --> how to check/verify?

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  #1  
Old 01-20-10, 04:39 PM
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blown transformer --> how to check/verify?

I didn't power off EAU at breaker when replacing Honeywell T8085D thermostat with Lux 1500 (possibly shorting the blue to the red wires). Now, I couldn't get the fan, A/C nor the heating started. I have a Comfortmaker furnace using a White Rodgers Main Control Board 50E47-130.

My questions are:

1. Power at the breaker is good, but couldn't measure power from the wirings. Is this confirmation that the transformer is fried?

2. Transformers are on the ones on the White Rodgers control board, correct?

3. What terminals to measure from the control board to verify the transformer is gone?

4. Do I need to replace with the exact same White Rodgers control board? Or, can I replace with another control board model (that is newer, better, cheaper?)

Thanks in advance.
 
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  #2  
Old 01-20-10, 09:05 PM
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It is unlikely that your control board is damaged.

Measure for 24 volts AC between R and C.

Turn off the breaker(s) to the air handler and check the control board in the air handler for a popped low voltage fuse. (Usually a 3 or 5 amp blade type automotive fuse)

This is a York example...


If a fuse is not present the transformer probably requires replacement.



 
  #3  
Old 01-20-10, 09:08 PM
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Not sure of your control board, but the transformers I have seen look like door chime transformers and are often mounted on the outside of the furnace. If you have a volt meter, you can check the secondary (low voltage) side for somewhere between 16 - 24 volts A.C..
If you do not have voltage when the breaker is on, you probably fried the transformer.
 
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Old 01-21-10, 05:34 AM
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Take a reading between R and C. Your board does not have a transformer.. The transformer should be by itself. So, the board should not be needed replacment.
 
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Old 01-21-10, 04:23 PM
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Is the picture below the secondary transformer? It measures 22V across. Is the primary transformer on the controller board?



However, there is still no voltage when measuring across R and C wires.





The link below is my White Rodgers controller board:

http://www.white-rodgers.com/wrdhom/...pg0278_281.pdf

When measuring across TH & TR of the control module, it does not have any voltage reading. L1 and TH measures about 125Vac.

Please advise where to go from here. Thanks.
 
  #6  
Old 01-21-10, 06:27 PM
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That is the transformer for your doorbell.
The furnace transformer is behind that furnace control board.
(Near the blower)

Zoom out some with your camera and post a bigger picture for better assistance.
 
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Old 01-23-10, 02:48 PM
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R and C measured no voltage. Does it mean the transformer is bad? Where can I find the transformer?





 
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Old 01-23-10, 02:53 PM
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zoom out pictures of furnace are below:





 
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Old 01-23-10, 04:47 PM
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The transformer is inside of the electrical box mounted in front of your blower. C and R on that terminal block connect to it.
 
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Old 01-23-10, 06:38 PM
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Originally Posted by samvee View Post
Where can I find the transformer?

Should be behind this the silver cover when the t-stat wires meet up.

Did you make sure you pressed the cover switch (top left) when you tried taking a reading?


The photo above, I don't like the ideal of the gas flex line going into the metal hole..... it's waiting for the metal edge cut the gas line.....
 
  #11  
Old 01-24-10, 12:20 AM
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I measured 24V across the transformer on the right side (with the cover switch pressed), but C and R terminal still has no voltage. With the transformer working, how come there's no reading across C and R?

What is the black box on the left side?





Where should I go from here?
 
  #12  
Old 01-24-10, 12:23 AM
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I measured 24V across the transformer on the right side (with the cover switch pressed), but C and R terminal still has no voltage. With the transformer working, how come there's no reading across C and R?

What is the black box on the left side?





Where should I go from here?
 
  #13  
Old 01-24-10, 04:56 AM
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Block on the left? Looks like it's a fan relay for your fan to run in "ON" mode when you switch the t-stat to "ON".

Make sure the wire from the transformer is in place on the strip/terminal on the back side of the cover where the R and C t-stat wire hook up is.
 
  #14  
Old 01-24-10, 07:23 AM
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I believe you mentioned that you were replacing the thermostat. Always go back and ask "what's changed?". It is possible that the two are shorted together somewhere. (Just an FYIshorted low voltage will not neccissarily cause a fuse to pop.) I recommend you disconnect the wiring to the thermostat (at the furnace first and the thermostat 2nd) to see if you now have voltage. If voltage present when disconnect wiring at furnace, then short in thermostat wiring or thermostat.
 
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Old 01-25-10, 02:09 AM
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The secondary voltage measured zero from the transformer, so that is why I am not picking up power across R & C. I measured the wrong wire from the transformer the night before...

Will stop by local hardware store to get a replacement transformer to try.

In regards to air filter for the furnace, what is the best kind? I heard that electrostatic filter will stress the system too much. Any truth to that?

Thank you ALL for your help!!
 
  #16  
Old 01-25-10, 06:05 AM
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I suggest the cheaper plete air filter. Not the 3M' ones.

Not sure what your hardware has, but Home Depot has the 3 pack NaturalAire that runs about $8 for 3.

Seeing your photo, looks like the air filter is not fitting right?
 
  #17  
Old 01-27-10, 10:56 AM
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Yea... the current filter the service guy previously jammed in there was 24x24x1. Our air filter size of 22x24x1 is not one we typically find instore. Know any reputable place online where they sell for cheap?
 
  #18  
Old 01-27-10, 12:06 PM
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I have not ordered any filters from online for custom size. Search around and find what you feel will be a good site.

sorry couldn't help you out there.
 
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