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Old 07-25-2020, 01:40 PM   #31
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


If the furnace tripped the high limit because the low speed wasn't working (or working well enough) it'll run in high speed until the limit resets and the timer expires. There could still be a problem with the board, but considering how cheap a capacitor is, it doesn't hurt either way. They wear out anyways.

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Old 07-25-2020, 01:46 PM   #32
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


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Originally Posted by supers05 View Post
If the furnace tripped the high limit because the low speed wasn't working (or working well enough) it'll run in high speed until the limit resets and the timer expires. There could still be a problem with the board, but considering how cheap a capacitor is, it doesn't hurt either way. They wear out anyways.

Cheers!
I suppose I can order a capacitor as well. Although not quite sure which one I need... Googling seemed to produce this? https://www.repairclinic.com/PartDet...xoCvoEQAvD_BwE


There are these two but not sure what the difference is despite them having the same 'model number'
https://www.amazon.com/Trane-CPT0097.../dp/B00RZXUZKA

https://www.amazon.com/CPT00977-Tran.../dp/B06XRN2WQY

Last edited by jplee3; 07-25-2020 at 01:49 PM.
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Old 07-25-2020, 02:21 PM   #33
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


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Originally Posted by jplee3 View Post
I suppose I can order a capacitor as well. Although not quite sure which one I need... Googling seemed to produce this? https://www.repairclinic.com/PartDet...xoCvoEQAvD_BwE


There are these two but not sure what the difference is despite them having the same 'model number'
https://www.amazon.com/Trane-CPT0097.../dp/B00RZXUZKA

https://www.amazon.com/CPT00977-Tran.../dp/B06XRN2WQY
Turn off power to the furnace and unscrew the bracket holding the capacitor on the blower. It'll have its ratings on it.

Cheers!
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Old 07-25-2020, 02:50 PM   #34
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


Your furnace just uses the a heating or cooling speed tap (most likely low heat) for continuous fan.

Everything should be thoroughly checked/ruled out and you shouldn't just throw parts at it.

Could be the board, low speed tap used for low heat, weak capacitor.

Your best option is to call a tech out unless you want to spend time learning.
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Old 07-25-2020, 02:52 PM   #35
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


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Originally Posted by supers05 View Post
Turn off power to the furnace and unscrew the bracket holding the capacitor on the blower. It'll have its ratings on it.

Cheers!
There's no label on it, and it looks ancient haha. No idea what the ratings would be but it has numbers on the bottom: "184290" ?




Looks like there's some minor rusting and possible corrosion. Seems like it should be replaced either way. Ughhh, I wonder if I should try to cancel the control board order (if it'll even cancel... I ordered one for $140 off Ebay)
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Old 07-25-2020, 02:56 PM   #36
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


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Originally Posted by user_12345a View Post
Your furnace just uses the a heating or cooling speed tap (most likely low heat) for continuous fan.

Everything should be thoroughly checked/ruled out and you shouldn't just throw parts at it.

Could be the board, low speed tap used for low heat, weak capacitor.

Your best option is to call a tech out unless you want to spend time learning.

Thanks, the capacitor definitely doesn't look to be in such great condition. I tried to do an ohm test against it but it was unresponsive... not sure if my multimeter is faulty though - it's a cheapo harbor freight one.

Was just chatting with RepairClinic and gave my model # and they came back with this capacitor as the correct replacement:
https://www.repairclinic.com/PartDet...T02642/4931109

Wondering if this would work: https://www.amazon.com/Motor-Run-Cap...17&s=hi&sr=1-1

EDIT: (seems like 7.5uf/mfd may not be the best idea if the original was 5uf/mfd, in which case https://www.amazon.com/OneTrip-Parts...dp/B007YWJZQC/)

Last edited by jplee3; 07-25-2020 at 03:08 PM.
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Old 07-25-2020, 03:17 PM   #37
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


OK, looks like the specs per the fan are 5mfd:



It says "CAP 5.00/370v"

I went ahead and ordered this - https://www.amazon.com/gp/product/B008OJMPRK/

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Old 07-25-2020, 04:02 PM   #38
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


UPDATE: I just went back and disconnected the capacitor completely - I was just observing it the first time. I tried using the Voltmeter (setting to 2000k or 200k ohms) to check and it seemed like it would pop up some numbers and jump around temporarily, then back down to 1 or 0 but not consistently. I noticed corrosion on the terminals so sanded it lightly with some sandpaper then popped it back into place then tried again and was getting more consistent results with the numbers jumping around and then going back to 1. Based on watching a couple youtube vids, this seems to indicate that the capacitor may still be functional...? But does that show that the capacitor is necessarily failing or going bad (which it sounds like *could* be attributed to the symptoms I'm observing with the fan not being able to run when called directly versus blowing via heat and cold air)?
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Old 07-25-2020, 04:55 PM   #39
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


ohm meter not very useful for capacitors other than telling that it's completely dead, need a meter that checks capacitance.
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Old 07-25-2020, 05:06 PM   #40
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


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ohm meter not very useful for capacitors other than telling that it's completely dead, need a meter that checks capacitance.
I had a hunch that might be the case - so it's possible that the mfd/uf could be reading something low like 1-2uf which might explain the behavior I'm observing. The replacement capacitor arrives tomorrow so let's hope for the best!

EDIT: what might explain why the fan appears to be running only when the hot or cold air are called btw? I think you mentioned that the fan might be running a lower speed when hot/cold air are running? Or is it something else? Like the fan motor/capacitor are getting 'energized' by the other components called when using heat or cold air but when called on it's own there's not enough power pushing through to it to turn on, etc? I think there were a couple ideas mentioned above but just trying to get a full understanding.

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Old 07-25-2020, 05:38 PM   #41
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


when the furnace is heating in first stage, the fan speed should be low - your board probably uses the same speed for continuous.

if the motor fails to start - just hums and gets hot in low heat and continuous mode, it's possible the capacitor is bad. often you can give it a little push to get it going.

I'm no fan of changing out parts to troubleshoot even though capacitors are cheap.
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Old 07-25-2020, 05:48 PM   #42
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


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Originally Posted by user_12345a View Post
when the furnace is heating in first stage, the fan speed should be low - your board probably uses the same speed for continuous.

if the motor fails to start - just hums and gets hot in low heat and continuous mode, it's possible the capacitor is bad. often you can give it a little push to get it going.

I'm no fan of changing out parts to troubleshoot even though capacitors are cheap.
In terms of stages, isn't my furnace only 'locked' into the first stage regardless since the W2 terminal isn't connected to anything? To my recollection, there seemed to be no difference in terms of amount of air being pushed out between when the fan was working previously and when I would have the hot and cold air turned on. I never realized that the fan could run in a lower speed but maybe I just didn't notice.

As far as the motor, I tried to listen when turning the fan on and couldn't discern if there was a hum or not - I didn't notice anything at least.

What would your method of troubleshooting be in this case? Just checking every part/connection with a voltmeter? I think the only other thing you mentioned was the low speed tap - that's something replaceable? And what does that look like?
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Old 07-25-2020, 05:53 PM   #43
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


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In terms of stages, isn't my furnace only 'locked' into the first stage regardless since the W2 terminal isn't connected to anything?
No - the board brings on second stage after a delay.

Quote:
What would your method of troubleshooting be in this case? Just checking every part/connection with a voltmeter?
See if the board is applying line voltage to the appropriate terminal (likely low heat) and neutral when there's a call for continuous fan (door switch needs to be depressed to do the test).

If the board isn't applying power to blower with 24v ac between G and C t-stat terminals on board, it's bad.

If it is, check capacitor and motor.
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Old 07-25-2020, 06:47 PM   #44
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


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Originally Posted by user_12345a View Post
No - the board brings on second stage after a delay.



See if the board is applying line voltage to the appropriate terminal (likely low heat) and neutral when there's a call for continuous fan (door switch needs to be depressed to do the test).

If the board isn't applying power to blower with 24v ac between G and C t-stat terminals on board, it's bad.

If it is, check capacitor and motor.


So I did the control board/fan blower bypass test where I plugged the fan directly into the switch and depressed the switch - the fan blower turned on and worked immediately. So I think this means that the motor and capacitor should be fine as those worked with a direct 120v connection. At this point, all signs point to the control board no?
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Old 07-25-2020, 06:49 PM   #45
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Re: Trane XL80/Ecobee AC seems OK but Furnace/Fan control not working?


did you use the wire normally connected to low heat?

if yes, ya you're looking at a board replacement.
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