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After piecing together several threads i was able to successfully fix my AC this morning... Just a THANK YOU to the forum... And I decided to contribute the details of my experience on the off chance it might help others...

PROBLEM: Upstairs zone not cooling... Compressor motor was running and was making a hissing sound as if a pressure release valve was open... the fan motor was NOT running and was VERY hot...

DIAGNOSIS 1: Assumed it was a bad capacitor... the capacitor (a 35/3) looked fine but i replaced it anyway (hoping i would not need a new fan motor)... after that, the fan started (hard) but the AC seemed to be otherwise working fine... of course, the fan motor died some time later with same symptoms...

DIAGNOSIS 2: I replaced the old 3 uF motor (the HVAC guy gave me a 5 uF motor and new 35/5 capacitor)... the fan motor was the issue and everything worked great after replacing it... needless to say, replacing a motor is a LOT trickier than replacing a capacitor...

LESSONS LEARNED:
1) Wiring can be confusing... my old motor had 3 wires, easy as pie... the new universal replacement motor had ~9 wires (supporting features like variable speed, reversible rotation, single/dual capacitor) so there was some sorting out to be done on the wiring side...
2) Retrofitting is a hassle... it was a pain to fit the motor into the old unit... had to flip the bolts, buy new nuts & caps, cut the shaft and heat/hammer out a dome in the grill to retrofit the new motor (i probably could have bought longer OEM motor bolts for a cleaner job, but who knows for sure) ...
3) Changing a capacitor can be confusing... I was worried about the change in dual capacitors given the change in fan motor (i thought i might need to wire in the 35/3 for the compressor and the 35/5 for the fan, but after verifying that the 35 side was for the compressor and the 5 side was for the (new) fan, i just wired the new 35/5 capacitor (and wrote off the new 35/3 capacitor)...
4) Wiring the fan motor can be confusing.... ignoring the variable speed wires was easy enough... wiring COM and HERM was easy too... but the FAN wiring was confusing because i had Brown AND Brown/White fan wires... I connected Brown to FAN and taped off the Brown/White (since it is apparently not needed in dual capacitor applications)... Of course, I needed to change the direction of rotation, so flipped the orange/yellow factory spades...

BOTTOM LINE: The AC is working great now... Not sure this was really a DIY type project... I spent almost $100 in parts, an hour on the road, 90 mins of labor, another hour researching online... i wonder what a tech would have charged... but no matter, i enjoyed the project and have a much better appreciation for HVAC work...
 

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Registered
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2,362 Posts
After piecing together several threads i was able to successfully fix my AC this morning... Just a THANK YOU to the forum... And I decided to contribute the details of my experience on the off chance it might help others...

PROBLEM: Upstairs zone not cooling... Compressor motor was running and was making a hissing sound as if a pressure release valve was open... the fan motor was NOT running and was VERY hot...

DIAGNOSIS 1: Assumed it was a bad capacitor... the capacitor (a 35/3) looked fine but i replaced it anyway (hoping i would not need a new fan motor)... after that, the fan started (hard) but the AC seemed to be otherwise working fine... of course, the fan motor died some time later with same symptoms...

DIAGNOSIS 2: I replaced the old 3 uF motor (the HVAC guy gave me a 5 uF motor and new 35/5 capacitor)... the fan motor was the issue and everything worked great after replacing it... needless to say, replacing a motor is a LOT trickier than replacing a capacitor...

LESSONS LEARNED:
1) Wiring can be confusing... my old motor had 3 wires, easy as pie... the new universal replacement motor had ~9 wires (supporting features like variable speed, reversible rotation, single/dual capacitor) so there was some sorting out to be done on the wiring side...
2) Retrofitting is a hassle... it was a pain to fit the motor into the old unit... had to flip the bolts, buy new nuts & caps, cut the shaft and heat/hammer out a dome in the grill to retrofit the new motor (i probably could have bought longer OEM motor bolts for a cleaner job, but who knows for sure) ...
3) Changing a capacitor can be confusing... I was worried about the change in dual capacitors given the change in fan motor (i thought i might need to wire in the 35/3 for the compressor and the 35/5 for the fan, but after verifying that the 35 side was for the compressor and the 5 side was for the (new) fan, i just wired the new 35/5 capacitor (and wrote off the new 35/3 capacitor)...
4) Wiring the fan motor can be confusing.... ignoring the variable speed wires was easy enough... wiring COM and HERM was easy too... but the FAN wiring was confusing because i had Brown AND Brown/White fan wires... I connected Brown to FAN and taped off the Brown/White (since it is apparently not needed in dual capacitor applications)... Of course, I needed to change the direction of rotation, so flipped the orange/yellow factory spades...

BOTTOM LINE: The AC is working great now... Not sure this was really a DIY type project... I spent almost $100 in parts, an hour on the road, 90 mins of labor, another hour researching online... i wonder what a tech would have charged... but no matter, i enjoyed the project and have a much better appreciation for HVAC work...
I would have had you up and running, along with checking the refrigerant and cleaning , in half hour to 45 minutes. Would have been double the cost though so good job.
 
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