Replacing AC capacitor

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Hey guys,

I need to replace the 27 year old capacitor on my home AC compressor unit. Unfortunately, the model is no longer manufactured. So I need a direct replacement.

What factors do I need to look for? It's a three blade "Aerovox Z26P4440W" which is an MPP film, 2.5" round can, 440 Volt AC voltage, 40mF capacitance, dual rating section type.

Any ideas?
 
Try an HVAC shop or a a company with internet service called Digikey, another internet option is Mouser. The unit is probably a standard part.
 
Actually, it goes even beyond that. You can use a 440V cap in place of a 370V - but not the other way around. You can also use HIGHER capacitance (microfarad) ratings, just not lower. Of course, as stated above, it needs to physically fit in the space.
 
Originally Posted By: Alfred_B
27 year old capacitor on my home AC compressor unit.


How did you get your unit to last 27 years?!?!?

10 years is about all they can take in Texas
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Originally Posted By: Crispysea
As long as the rating is the same, the terminals are the same, and it can physically fit, it will work. I see a matching one on Home Depot's site, so it's a common part. There should be a second rating for the other section, probably 5mF.


on the label is says 35+5 mF

Is it this one you found on HD?

http://www.homedepot.com/p/Packard-440-V...FD355/204415834
 
Originally Posted By: DBMaster
Actually, it goes even beyond that. You can use a 440V cap in place of a 370V - but not the other way around. You can also use HIGHER capacitance (microfarad) ratings, just not lower. Of course, as stated above, it needs to physically fit in the space.


Thanks, very good information to have.
 
Yes, you're right. It's safe to use higher voltage rated capacitors, but they often cost more. I restore antique radios, and they usually contain at least one can capacitor like this.
 
Originally Posted By: Crispysea
Yes, you're right. It's safe to use higher voltage rated capacitors, but they often cost more. I restore antique radios, and they usually contain at least one can capacitor like this.
I do Drake and Collins, what do you restore?
 
Originally Posted By: DBMaster
You can also use HIGHER capacitance (microfarad) ratings, just not lower.


It depends where in the circuit the cap is used, what component(s) are draining the cap. E.g. if its for AC rectification generally a bigger cap will do a better job of smoothing, if its for noise suppression you do not want to change the cap value much.

As this is a capacitor normally used as for a motor its important to keep to a close capacitance as to correctly regulate the amount and timing of current to the AC fan and compressor motors.
 
I'm guessing this is the starter cap on the compressor? If that's the case you want to find one with as close to original capacity as possible.
 
How did you get your unit to last 27 years?!?!?

10 years is about all they can take in Texas
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If north of the Mason Dixon line it only needs to work a few months a year. I have only needed the AC to pull humidity this summer 5 days. Maybe tomorrow it may get to 85 with good chance of storms so will start the unit to pull water and keep the dogs happy.
My folks have a original install unit that was put in in 1975
 
Definitely not 40uf. It is a dual section cap with a 35uf section and a 5uf section. 35uf for the compressor, indicated by the terminal that should be labeled Herm (hermetic compressor). The 5uf section is for the condenser fan and should be labeled Fan. The "C" terminal is the common for the two sections. I would run a Titan HD cap. They are made in the USA and good quality. Titan HD
 
Jim_Truett

When the compressor shuts off and won't come back on, that's usually because the capacitor is worn out; correct?
 
I had a problem with my AC blowing warm air. The compressor would come on, the AC blew like normal for hot second, then the AC would blow warm air. I went out to the exchanger, figured out quickly the fan wasn't coming on and the compressor was overheating and shutting off. After allowing it to cool down, I had my wife turn it on, then I gave the fan blade a starting assist with a stick. It then worked like normal, so I concluded the exchanger fan motor capacitor was bad.

Ordered another dual capacitor, then took the old one out and tested it after googling the procedure. The fan side was bad, as the simple test with a Volt Ohm meter indicated. This is a smarter test than using a stick, but I never said I was the sharpest tool in the shed.

Here is a good video on testing the capacitor: https://www.youtube.com/watch?v=PBoOx8YzD_s
 
I ordered a $14 capacitance tester on eBay - from Korea. It works very well and makes testing easy!
 
I had my capacitor fail on an outdoor heat pump compressor/condenser/fan cube unit before. Old one was bulged like a soda in the freezer.
Installing the new one was as easy as anything I've ever done. And it was cheap too. I checked the part number of the old one, got an interchange number, ordered one off Amazon or eBay (forgot which), and a couple of days later the system was up and running again.
 
Originally Posted By: Linctex

How did you get your unit to last 27 years?!?!?
10 years is about all they can take in Texas
21.gif



Last week, a distant neighbor had his outdoor compressor replaced because it finally seized. It was a Friedrichs and was originally installed in 1978.
I know Kansas doesn't have the length of summer that Texas has (I've lived in both states, BTW), but we get some heat here also, as last Saturday was 105 degrees.
Anyway, your older R22 units lasted a lot longer than your newer R410a compressors and indoor coils. One step forward and two back. Or, in this case, three steps back.
 
^agreed. My outdoor unit is now 12 years old. It's a 10 SEER R-22 unit. I work it hard, 71 degree setting in summer. I clean the outdoor coil once a year. I've cleaned the indoor coil once in 17 years. I sealed around the filters with rubber weatherstripping so I found the evaporator coil stays clean enough. I'm not sure if it's high efficiency designs that hurt longevity or the sourcing of the cheapest components possible.
 
Originally Posted By: Merkava_4
Jim_Truett

When the compressor shuts off and won't come back on, that's usually because the capacitor is worn out; correct?


Does the condenser buzz when it doesn't restart?

The capacitor causes the motor to rotate due to a phase shift on one of the windings. Capacitor failure generally causes the motor to stall at startup and trip a breaker or blow a fuse. You should be able to hear the 60hz buzz coming from the compressor. The cap is due for replacement at its age. It sounds like you should investigate the contactor as well. Check the coil for 24vac from the thermostat when it is calling for cooling, and make sure you are seeing contact closure and 120vac to ground through both poles when commanded to run.
 
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