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HVAC Condensor fans stalls during cycle

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  • Sep 1st, 2020 5:30 pm
[OP]
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Jun 21, 2003
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Stoney Creek, ON

HVAC Condensor fans stalls during cycle

I am at my wit's end here trying to figure this out. The fan on my A/C condenser unit is stalling out mid-cycle and I can't seem to figure out what further to test. My wife and I have both been off for months due to COVID so I'm trying my best to solve the issue to get us through the last few weeks of use with the intent of a full A/C + furnace replacement when we are working again. My daughter's room gets too hot (~76-80 during the day in to night, even when the rest is 4 degrees lower) in our home due to afternoon sun so unfortunately we need to try and get this running for a bit longer.

It starts no problem and the issue only seems to pop up after running for awhile.

Things I've done:
-Tested that the caps charge from a multimeter (I don't have a capacitance meter)
-Topped up the 2 oil ports in the fan motor (it's an old unit)
-Verified the shaft can spin no problem
-Measured resistance on the leads, and they appear OK. (Black to yellow: 45.5, Black to brown: 93.7, Yellow to brown: 138.5 -- No connection on any lead to ground)
-Verified 240V at the unit.

I have no idea what more could possibly be checked with this stupid thing. If I understand correctly the capacitor ONLY applies during the start up correct, so even if it is dying (can't confirm the condition due to lack of capacitance meter) and the fan can start that shouldn't be the problem right ? Any other thoughts on things to take a look at ?

EDIT: I sat at the unit while it ran and waited it out until it stalled. While everything is running fine the voltage between black (common) and brown is 225v. When I started to hear the fan slow down I measured again and the voltage had dropped to 89V, and stayed at 89V when the fan stalled
Last edited by ChicoQuente on Sep 1st, 2020 9:30 am, edited 1 time in total.
12 replies
Deal Addict
Jun 16, 2009
3054 posts
1400 upvotes
Woodbridge
Capacitor also stabilizes the voltage and helps running the fan. Ofcourse the main function is to start the fan. Possibility of having a defective cap cannot be ruled out from the description you have given above. However it seems that your motor is dying as when it gets heated after running a short while, it stalls. If you have access to dual cap, than replace it regardless as even with a new motor, it should be replaced ( I am not advocating this to be DIY job unless you know what you are doing 100%. AC runs on 220V so one has to be extra cautious).
ChicoQuente wrote: I am at my wit's end here trying to figure this out. The fan on my A/C condenser unit is stalling out mid-cycle and I can't seem to figure out what further to test. My wife and I have both been off for months due to COVID so I'm trying my best to solve the issue to get us through the last few weeks of use with the intent of a full A/C + furnace replacement when we are working again. My daughter's room gets too hot (~76-80 during the day in to night, even when the rest is 4 degrees lower) in our home due to afternoon sun so unfortunately we need to try and get this running for a bit longer.

It starts no problem and the issue only seems to pop up after running for awhile.

Things I've done:
-Tested that the caps charge from a multimeter (I don't have a capacitance meter)
-Topped up the 2 oil ports in the fan motor (it's an old unit)
-Verified the shaft can spin no problem
-Measured resistance on the leads, and they appear OK. (Black to yellow: 45.5, Black to brown: 93.7, Yellow to brown: 138.5 -- No connection on any lead to ground)
-Verified 240V at the unit.

I have no idea what more could possibly be checked with this stupid thing. If I understand correctly the capacitor ONLY applies during the start up correct, so even if it is dying (can't confirm the condition due to lack of capacitance meter) and the fan can start that shouldn't be the problem right ? Any other thoughts on things to take a look at ?
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[OP]
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Jun 21, 2003
4802 posts
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Stoney Creek, ON
newlyborn wrote: Capacitor also stabilizes the voltage and helps running the fan. Ofcourse the main function is to start the fan. Possibility of having a defective cap cannot be ruled out from the description you have given above. However it seems that your motor is dying as when it gets heated after running a short while, it stalls. If you have access to dual cap, than replace it regardless as even with a new motor, it should be replaced ( I am not advocating this to be DIY job unless you know what you are doing 100%. AC runs on 220V so one has to be extra cautious).
As you posted I added an edit. Also starting to think it's the cap since the voltage dropped.

I think the overheat and stall is a result of that voltage drop and it trying to pull more current to compensate.

Also, I'm an electrician so completely comfortable safely swapping parts. I'm just rusty on the electronic components theory like a capacitor.
Last edited by ChicoQuente on Sep 1st, 2020 9:44 am, edited 1 time in total.
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Jun 16, 2009
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I am glad to provide you helpful diagnostic and little relieved to know that you wont electrocute yourself in the whole process.
ChicoQuente wrote: As you posted I added an edit. Also starting to think it's the cap since the voltage dropped.

Also, I'm an electrician so completely comfortable safely swapping parts. I'm just rusty on the electronic components theory like a capacitor.
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Jun 12, 2007
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Is this a multispeed condenser fan?

(i.e. the fan speed speed switched from low to high, but high speed is screwed up)
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Woodbridge
Even though OP can answer precisely, my assumption is its a single speed condensor fan. The new gen 2 stage AC's with various speeds do not have capacitors.
l69norm wrote: Is this a multispeed condenser fan?

(i.e. the fan speed speed switched from low to high, but high speed is screwed up)
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newlyborn wrote: Even though OP can answer precisely, my assumption is its a single speed condensor fan. The new gen 2 stage AC's with various speeds do not have capacitors.
I'm thinking about some of the older units with a 2 speed condenser fan motor that is controlled by a temp switch. Those still use a capacitor. If the temp switch contact is screwed up, the fan won't spin at that speed but the voltage on the winding (that does still work) drops from 220V to like 60-80V instead of 0V due to induction

Example :
(*** Note *** this is just an example, the OP wiring might be totally different)

Yellow to brown is high speed , black to brown is low speed.

When the unit starts up in low speed, black to brown (low speed) = 220V.

When the unit switches to high speed, yellow to brown (high speed) is 220V, but black to brown (low speed) doesn't drop to 0V, it's around 60-80V due to induction

Edit - older Trane units had a 2 speed condenser fan motor controlled by a temperature switch:

Image

trane part number THT00741

When the outside air temp is lower, the condenser fan runs at slow speed = less noise. When the outside air temp starts getting hot, the condenser fan switches to high speed
Last edited by l69norm on Sep 1st, 2020 9:54 pm, edited 1 time in total.
[OP]
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Jun 21, 2003
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Stoney Creek, ON
l69norm wrote: I'm thinking about some of the older units with a 2 speed condenser fan motor that is controlled by a temp switch. Those still use a capacitor. If the temp switch contact is screwed up, the fan won't spin at that speed but the voltage on the winding (that does still work) drops from 220V to like 60-80V instead of 0V due to induction

Example :
(*** Note *** this is just an example, the OP wiring might be totally different)

Yellow to brown is high speed , black to brown is low speed.

When the unit starts up in low speed, black to brown (low speed) = 220V.

When the unit switches to high speed, yellow to brown (high speed) is 220V, but black to brown (low speed) doesn't drop to 0V, it's around 60-80V due to induction
I can confirm this is single speed. There is nothing to control speed at all, confirmed visually and with the schematic.

My wife reached out to an old friend that happens to be I. HVAC and they are grabbing me the 2 capacitors at their account pricing. Hoping to get them today as it is quite toasty in here. Fingers crossed that is the fix. It's pretty much the only paid repair we're willing to do at this stage as we have every intention of replacing it.
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May 30, 2010
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I vote for the capacitor too. Might as well replace it first and then troubleshoot the rest. It's an open circuit to DC, and a resistor to AC, as more current flows, it heats up the dielectric material, as the dielectric material ages, it's more prone to drop it's resistance, hence the drop in voltage after start. It's a common failure point, and regardless of the final repair, a new capacitor would be included anyway.
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Mar 13, 2004
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Ontario
Interested in the result/fix of this. But as others have said Capacitor would be the first thing to try (as it seems like you already are)
[OP]
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Jun 21, 2003
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Unfortunately after replacement it still stalled out after 15-20 minutes. I guess at this point the only thing left is the fan motor.
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No harm done. Capacitor needed to be replaced regardless when changing the motor. If you need me to source one for you, let me know, I try to help tradesman ( at no cost).
ChicoQuente wrote: Unfortunately after replacement it still stalled out after 15-20 minutes. I guess at this point the only thing left is the fan motor.
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