Trane XE90 blower problem

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Old 07-30-08, 04:25 PM
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Trane XE90 blower problem

Strange problem,
If I switch my furnace to "heat" mode, it goes through the ignition process, flame lights, and then after a few minutes shuts down from over temp because the blower motor never came on.

But if I switch the unit to AC... it does fine. Blower cycles on each time the thermostat calls for cooling.

And finally, if I switch the thermostat fan switch from "Auto" to "Fan On", the blower does not come on. The only time to blower comes on is when the unit is in the cooling cycle and the thermostat is calling for cooling.

The only thing I know to do is to replace the logic board. I appreciate any suggestions from anyone.
 
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Old 07-31-08, 09:05 AM
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Originally Posted by lwillisjr View Post
Strange problem,
Indeed.... see below..

-If I switch my furnace to "heat" mode, the blower motor never came on.

-But if I switch the unit to AC... it does fine. Blower cycles on

-And finally, if I switch the thermostat fan switch from "Auto" to "Fan On", the blower does not come on.
I find this very odd if the blower does not come in with the t-stat fan switch to ON. Anytime the A/C is called for the stat inside "turns on the blower". Have you used this witch in the past?

At the board, remove the G wire, and jumper between R and G at the furnace. (Door switch needs to be pressed for power.) If the blower does start, then remove jumper and put back the G wire..

At the stat, do the same as above, Remove G wire, and jumper between R and G.. If the fan starts, then you may have a bad fan ON switch at the stat.

As for the fan not starting up in heating mode, You will need to use a meter to see if you have power coming out of the HEAT tap on the board for the blower.
 
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Old 07-31-08, 05:12 PM
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Tried new thermostat

This problem first started with the original thermostat. So without testing, the thermostat was the first thing I replaced (also excuse for new programmable thermostat). But the exact same problem persisted. I will try testing as you have suggested, but I don't think it is the thermostat.
 
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Old 08-02-08, 10:25 AM
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And if you find the heat tap on the board, disconnect that wire to the motor and check that heat winding in the motor for continuity (an actual ohms reading, actually) to neutral, or a short. You can have one winding speed bad in a motor while yet another one works.
 
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Old 09-22-08, 04:42 PM
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Still diagnosing

I greatly appreciate the feedback. Since the fan works on the cooling I've been slow to diagnose this further. Now that fall is around the corner I need to get serious.

Everything tests fine at the thermostat. At the furnace itself I disconnected the "G" wire, and shorted it to "R". I hear the relay on on the controller board "click", but the fan doesn't come on. I disconnected the fan wires and measured both the "cool" and "heat" fan connections with the "R" and "G" tabs shorted on the controller board. I don't measure 115V on either fan connector connector. I also measured the resistance on the fan windings themselves, and measured 2 ohms on one and 1.8 on the other. It would seem to me that something is wrong with the controller board.

Since everything works on the cooling cycle, is it OK to switch the 2 fan winding connections just to make sure that both windings are working?

Also, there are 2 fan wires that are labeled "park" on the controller board. Anyone know what these are for.

Thanks again.
 
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Old 09-22-08, 05:50 PM
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Originally Posted by lwillisjr View Post
Since everything works on the cooling cycle, is it OK to switch the 2 fan winding connections just to make sure that both windings are working?
Yes you can switch the wire around.

Also, there are 2 fan wires that are labeled "park" on the controller board. Anyone know what these are for.
Most motor are multi-speed ( 4 speed) and the board only needs two.. 1-heat, 2-cool. so only 2 of the 4 speed is used, and the unused wire is placed on the "parked" spade (dead)
 
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Old 09-30-08, 02:50 PM
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Thank you !

Jay11J,
Just want to say THANK YOU for this forum and your input. It took some time but all diagnosis for this unique problem pointed to the controller board. I found an excellent website and bought a new one at a great price. I have successfully replaced the controller board and all works now.

Thanks again!
 
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Old 09-30-08, 03:02 PM
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Glad to help out, and thanks for the update..

Stay warm this winter!
 
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