My Trane furnace lock out, transfomer sec is 56V. Need help!!


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Old 10-31-13, 11:19 PM
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My Trane furnace lock out, transfomer sec is 56V. Need help!!

I have Trane furnace UE080A936. Several days ago, I switched the Thermostat from Cool to Heat. The furnace would not respond. The AC is fine, but the furnace won't work. The blower is on, when I put the fan in ON position in heating mode, The red diagnostic LED only flash one and hear one click sound form the control board, when I switch the main power to ON. Then the LED is off all the time. I did check IN (LINE) and OUT (XFMR) of the main power source to control board is good (120V). But the output (TH and TR) of the transformer is 55V. The voltage of terminal W & C is zero, but the R & C is 55V. I had replaced control board around several months ago (from White Rodgers Model 50A50-571 to 50A55-843). Will the 55V from the transformer locked out the furnace? (I did check the resistance of the transformer, Pri is 19 ohms and sec is 0.8~0.9 ohms. Is it still good?) (When AC is running and work fine when I check the voltage between Y & C terminal (55V))
 
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Old 10-31-13, 11:40 PM
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If you're sure that the readings are accurate, change the transformer - odds are that the board will need to be replaced after being subjected to 56v instead of 24v.

Other low voltage electrical components may need to be changed including the t-stat. (especially if it's digital/electronic)
 
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Old 11-01-13, 02:39 PM
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Personally I'd check very carefully to determine if the voltages you report are measured correctly. Sometimes digital voltmeters can give erratic results, or you might be measuring the voltage incorrectly in some way.


I'd be a lot more suspicious of one of these as the cause of the measurements you report than a transformer that is actually putting out 56 volts. Could be, of course --- but very unlikely in my experience.
 
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Old 11-01-13, 06:46 PM
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I too suspect an error in measurement. Are you sure you are measuring AC volts?
 
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Old 11-02-13, 06:40 AM
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Thank you for the responds!! You all are right. I made the wrong measurement (put in DC mode). The correct readings are as below.

I have Trane furnace UE080A936. Several days ago, I switched the Thermostat from Cool to Heat. The furnace would not respond. The AC is fine, but the furnace won't work. The blower is on, when I put the fan in ON position in heating mode, The red diagnostic LED only flash one and hear one click sound form the control board, when I switch the main power to ON. Then the LED is off all the time. I did check IN (LINE) and OUT (XFMR) of the main power source to control board is good (120V). But the output (TH and TR) of the transformer is 28V. The voltage of terminal W & C is zero, but the R & C is 28V. I had replaced control board around several months ago (from White Rodgers Model 50A50-571 to 50A55-843). Will the 28V from the transformer locked out the furnace? (I did check the resistance of the transformer, Pri is 19 ohms and sec is 0.8~0.9 ohms. Is it still good?) (When AC is running and work fine when I check the voltage between Y & C terminal (28V))
 
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Old 11-02-13, 09:01 AM
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To see if the furnace or the thermostat (including interconnecting wiring) is at fault, install a jumper between R & W at the furnace. If the furnace fires, the thermostat or wiring is the problem.
 
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Old 11-02-13, 12:17 PM
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Hi Grady,

Thank you so much for your advice. I did put jumper between W & R, The furnace run as normal. So, how can I test the Thermostate or faulty wiring?
 
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Old 11-02-13, 02:55 PM
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Not Grady, but since he isn't on and I see you are, go to your stat and remove the cover and do the same jumper there. If it runs normally, that tells you the wiring is ok. Then it's the stat IMO.
 
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Old 11-02-13, 07:46 PM
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Hi Tinmantu,

Thank you for your advice. I did what you said and found out the problems were from Thermostat. I had replaced a new one this evening and my furnace is run as normal. I hope the problems are solved.

Thank again to all who gave the advices.
 
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Old 11-03-13, 04:36 PM
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Good deal. Glad you got it fixed.
Thank you, Tinmantu for covering for me. That's' exactly what I'd have told Chester168 to do. Good Job.
 
 

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