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Old 11-12-2012, 09:22 PM   #1
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Air conditioner & heater sometimes won't turn on

Trane XE90
White Rodgers 50A50

I just moved into a house this past spring and noticed the central air unit sometimes will not turn on the air conditioner or furnace. When the unit doesn't click on, sometimes an old-fashioned smacking or fiddling with the wire harnesses will get it to work. When it does turn on, the control unit relays will click multiple times. And sometimes when it's running, it will just cut out and everything will stop.

With the original control unit, when the system does not work, the LED will be off. I believe constant flashing means it's working. At least that's what it does when the system works. A couple times I got a 4-flashing LED code, but I don't have the manual for this unit.

Because the relay clicking didn't sound right, I decided to replace the control unit with a universal model, White Rodgers 50A55. With this unit, the fan will constantly run and the LED will flash 5 times which the manual says is an open rollout switch. Visual inspection of the 2 rollout switches look OK. But would this cause the AC not to work, too?

Misc notes:
- I tried 3 different thermostats and got the same results.
- The installer apparently hardwired the door safety switch. So I thought maybe that was getting periodically disconnected somewhere. But I can't even find the darned wire.. It looks to be internal to the unit.
- When replacing the control unit, I inspected all the wires and connectors and they looked OK.
- With the replacement control unit, the smacking and wire harness jabbing methods didn't work anymore. So I put the old control unit back.

Anyway, does this sound like a rollout switch problem? I'm wondering if the problem is something else (like the door safety switch), since I have the same problem when trying to use the AC.

Thanks in advance for your help.



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Old 11-12-2012, 09:36 PM   #2
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Does your gas valve look like this, with two wiring harness' that connect into it, ignition and control?


Doc Holliday is offline   Reply With Quote
Old 11-13-2012, 12:40 PM   #3
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I don't think that's it. Here's a pic of my gas valve.

Btw, typo on top-- the model is Trane XE 78, not 90.
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