Trane XL 1200, click, hum no start

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  #1  
Old 05-26-19, 02:03 PM
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Trane XL 1200, click, hum no start

Trane 1200 XL, 1992 mfg. Date. Model TTX024C100A

So, I am fairly good with electrical items but if I can avoid it I will.
Bought my first house last year knowing that I would have a several years left in the hvac possibly.
Had an issue last year with it not turning on at one point but at the same time it would not kick the blower on. Quick couple resets at the breaker and it fixed the problem whenever it cropped up. I suspected a control voltage issue maybe but didnt do anything with it at the time. Replaced my house thermostat with a Nest unit and did not have the problem since.
Now since last year the first time I am trying to run it, the unit will not turn on....
The system obviously thinks it did as the blower is coming on for the house.
opened the panel for the unit and all fuses are good, get a good click from the unit as it gets the signal to turn on, and I see the contact move etc.
There is a humming that starts to build for the first 20ish seconds then it will stay at that volume.
The fan spins freely no issues there.
My first thoughts are the starter relay and the associated caps, am I skipping over something more obvious? Should I try to force start the fan etc? Trying to source parts for this hopefully wont be too bad. Looking like less than 70 bucks for the 2 caps and starter.





 
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  #2  
Old 05-26-19, 02:11 PM
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Welcome to the forums.

If the contactor closes and you hear humming..... it could just be a capacitor problem. If the fan doesn't start immediately the compressor will shut down on high heat. Don't leave it cycling like that as it's hard on the compressor. You could try giving the fan a push with a stick to see if it takes off. If it doesn't try the cap(s) first.
 
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Old 05-29-19, 06:54 PM
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So just an update. Pulled the system apart and did some further investigating...its apparently not the 2 caps I thought nor the stater relay. Suspected the 3rd cap...now but doesn't appear to be it...

Checked with my Fluke 179 meter

Starter Cap - 144uF (135-155)(resistor removed, re-soldered on after check) - checked ohm as well good as expected.
2nd Cap - Resistance slowly climbed as expected of a good cap (not sure on rating - not labeled)
3rd Cap - 4uf 370VAC (Z97F5504) - checked...came out good, very corroded at terminals, poor connection possible.
Starter Relay - GE 3ARR3J4A4 - Check the 1-2 poles, closed, resistance at 0.1-0.2 ohms when checked across. Open when unit is turned on.

Cleaned the terminals of the 3rd cap but still heavily corroded, ordered a replacement ($9) just incase.

Put new wire ends on several wires due to corrosion (more so on the 3rd cap), checked the remaining connections with nothing evident.

Contactor is a bit noisy still even though it moves, still cannot force the compressor/fan on.

Last items to eval is the contactor and the internal thermostat relay. May just order a contactor to be safe ($11)

Sigh...
 
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Old 05-29-19, 08:03 PM
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The 4uf capacitor is the one for the fan. The other two are for the compressor.

With everything connected as normal..... check the voltage at the top and bottom of the contactor. They should be the same...... +/- 240vAC with the contactor closed..
 
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