Trane system troubleshooting help needed

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Old 10-15-17, 03:46 PM
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Trane system troubleshooting help needed

Hi,
Earlier this week I noticed that my home got very warm right before I went to bed. I checked the thermostat and everything looked normal, except the temperature, but I did not hear the blower running. I went into the attic and saw that the coolant line was frozen solid all the way from the attic to the compressor.

I killed the power and let it thaw for about 24 hours. When I tried it turned everything back on, The outside compressor would cut on but the blower would not run. The blower motor and the capacitor are probably less than 5 years old as I remember replacing them not to long ago.

I hooked up the fan directly to 120 and it fired right up. I assumed that the relay on the board had gone bad so I hooked up the fan to the door switch and ran it like that for a few days until I could get the part. It cooled fine and the compressor would cycle on and off with the thermostat without issue, of course the fan would run continuously.

My new control board, a White Rogers 50A55-843, arrived and I installed it this morning. It seemed to be a fairly easy install. When I put the unit back together I noticed that the blower motor is running continually regardless of what the thermostat is set to or turned on or off.

I noticed that I am getting a diagnostic code of 5 flashes which indicated flame rollout detected. Of course with this new control board, I get no heat or cooling. If I plug up my old board then I can get cooling but the blower motor will not run unless I wire it straight to 120 volts.

I do not seem to be getting a rollout error on the old board since the compressor will turn on, but I am nto sure as the diagnostic LED on the old board does not light up.

I checked the transformer and I think it is working. I am getting 110 volts into the transformer into the and I am getting 28 volts on the output. I seem to be getting about 40 ohms resistance on the high side of the transformer and about 20 ohms on the output side. Although the low side seemed to fluctuate down to about 2 to 4 ohms occasionally but I am using an expensive meter instead of a Fluke so that may not be very accurate, but the high side was always consistent.

I am showing about 4 ohms resistance on both thermal sensors but I do not show any voltage running across this.

I am also not showing any voltage on the thermostat connections inside the furnace or at the thermostat itself. I am guessing that the thermostat is working as I could activate the compressor with it when I had the old board installed.

I also need to disclose that the replacement control board was an open box unit as that was all that was in stock at the moment.

Can someone give me any advice as to what I should check or look at next? I am suspecting it is a 24V problem but I wanted to check with someone who knows more than I do.

Thanks,
William
 

Last edited by Saxy13; 10-15-17 at 03:49 PM. Reason: Formatting
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  #2  
Old 10-15-17, 03:59 PM
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Welcome to the forums.

Too much information.

If your getting a diagnostic light blinking.... the transformer and low voltage is fine. Since you are getting a high heat sensor code..... you did not hook up the sensor lines correctly to the new board.

This will not be an easy thing to diagnose thru the internet. The conversion from your old board to your new board should have the correct wiring info on it. You will probably need to double check it,
 
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Old 10-15-17, 04:55 PM
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Thank you for the welcome to the forums and for the quick reply.

I am sorry to dump so much information. I knew it was a lot but I wanted to make sure I told the whole story. I went back and checked the sensor connections to my new board. It is a yellow wire that seems to connect between all of the sensors. This wire connects to the control board a plastic 12 wire connector. This connector can only be plugged up into one place and in one orientation. I seem to have continuity on that circuit from the top pressure switch all the way to the pin that plugs into the system board.

When I switched the boards I moved the wires over one at a time and they all seem to be plugged up to the right spot as best I can tell. Is there another sensor wire that plugs up somewhere else that I should be looking at?

Thanks,
William
 
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Old 10-15-17, 05:17 PM
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The pressure switch is on it's own line.
There is a different line for the high heat and rollout switches.
 
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Old 10-15-17, 07:40 PM
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Pete,

Thanks for your assistance with this. I have solved my issue. I had to put a jumper wire in to connect ro1 and ro2 on the 12 pin connector as my furnace is older and does not have these wires. Unfortunately this was not listed in the instructions. Once I put the jumper wire on, everything is working correctly.


William
 
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Old 10-16-17, 11:28 AM
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Great job. Thanks for letting us know how you made out.
 
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