Trane XE80 not sending 120v to transformer

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Old 05-27-20, 04:45 PM
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Trane XE80 not sending 120v to transformer

This unit fired up correctly the first couple of times I tried it, but then shut off. I cleaned the flame sensor and from then on the furnace is completely in-active. I put a new flame sensor on it and still nothing works.

the fuse tests good

The LED does not light, ignition sequence does not begin now ... nothing.

I disconnected the transformer wires and fed 120v directly into it ... the transformer works well and puts out a no-load voltage of 26 volts

the wires to the primary side of the transformer have no voltage on them from the board.

anyone got any ideas ??
 
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Old 05-27-20, 05:05 PM
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Welcome to the forums.

Did you check simple things like the blower door safety switch ?
That switch must be in to get 120vAC to the control board.
Check for 120v TO the board.
 
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Old 05-29-20, 05:58 PM
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Things Iíve tried

Yes, I taped the cover switch and then, in case the switch was defective I continuity tested it.

The board is hot on the 120 side, just nothing coming to the transformer so thereís no 24v control voltage.

when I clipped 120 directly to the transformer, I got 26v on the secondary, but I didnít want to try it with the secondary connected to the board. I didnít know if I might blow the board.

the crazy thing is, the first few times I tried starting the furnace, it went through the ignition sequence perfectly. The burner fired right up, but then it shut down. It did that more than once. But not once did it give me an error code (the LED stayed steady). So, I replaced the flame sensor on general principles.

now, since that time the LED does not light or blink.

if one of the flame roll out sensors or the limit control is bad could that trip a relay that keeps 120v from going to the transformer ?

Thanks

Allen
 
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Old 05-29-20, 06:33 PM
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It alright leaving the secondary connected when you power the transformer with alternate power.

The problem is your board. There are typically 4-6 flat slides in a row for neutral and 2-4 for hot/line.
Those terminals are all connected together on the board. There is nothing on the board to keep the
120v off the transformer if the board is powered.

Post the board model number for me.
 
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Old 05-30-20, 06:23 AM
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I replaced the board and igniter. Trane has gone to a 120v igniter. the original was 70v. The results with the old board and the new board are identical. Thatís why I was wondering if something outside the board could be shutting down the board.

here are the numbers on the original board :

D341396PO1
CHT03076
156-5183
 

Last edited by PJsDad; 05-30-20 at 06:47 AM.
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Old 05-30-20, 09:01 AM
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CHT03076
Is that correct ? Should it be CNT3076 ?

I'm not sure what your problem is there. The connections are fairly basic. Look at the picture below.
The five terminals in the white box are all neutral. The devices connected can be in any order. One of the terminals is labeled XFMR N for neutral to the transformer.

The two terminals in the red box are connected together. One is line/hot in and the other is transformer hot..... XFMR H.

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That’s why I was wondering if something outside the board could be shutting down the board.
There is nothing on the board that runs on 120v. It's all run completely by 24v. The 120v to that board supplies the 24v transformer and 120v power to the relays for blower, inducer and igniter.
 
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Old 05-30-20, 05:28 PM
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Suspecting the transformer then

Thanks so much for your insight on the grouping of the connections on the board. Very helpful.

Based on this I think I will put on a different transformer and bring 24v into the board without using any of the original internal wiring.

There obviously is some break in the chain, whether a bad wire or the transformer doesnít function when you put a load on it ... something is stopping 24v from being supplied to the board, so I will wire up a totally fresh 24v power source.

It will be several days before I get back to that property, but Iíll post my results when I do.

Thanks again.
 
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