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Espy 11-18-2008 01:55 PM

Trane XE 80 Problem
White-Rodgers 50A65-475 circuit board. LED is continuously off indicating no power. However, the fan runs continuously.

My suspicion is that lightning may have fried the circuit board. Everything *was* working before. It is possible that the A/C is working but I'm not 100% certain; the temperature does drop though slowly, perhaps. However, the heat never starts and again, either way, the fan runs continuously.

The LED is supposed to flash once when power is first turned on as it does its self-check but now nothing happens.

I don't want to replace the circuit board (50A65-475) until I can absolutely confirm that is the problem. I am a little confused that the fan runs continuously when power is on to the system. Is that on a different circuit with a default of "on"? The thermostat fan setting is "auto", not "on".

Is there an obvious test I can try (with a multi-meter, perhaps) to verify the circuit board needs to be replaced? Is there something else that might be the issue here?

If I do have to replace the circuit board, will any 50A65 do? It seems the 475 model has been superseded. Finally, where's the best place to get a replacement? I found a 50A65-843 on an HVAC website for about $190. Should I be able to do better than that?

Many thanks in advance for all help.

biggles 11-18-2008 05:20 PM

if you have a good 24V at the board on power into it the board is shot.....that fan cconstantly might be a relay within that works on having power to open the fan control (relay) in auto.

kennzz05 11-18-2008 05:31 PM

look at the wireing diagram and look for the limit circuit many times if the unit is in the middle of a heating cycle and power goes out as in a storm it causes the furnace to overheat and trip a limit especially if its a downflow unit most limits reset automaticly however some have to be reset if youre savy enough with a meter you can read the entire limit circuit at once thru the wires (diagram)

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