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tl;dr - What should I be searching for in documentation to find the correct capacitor for my outdoor AC unit or what inputs do I use to calculate the appropriate capacitor?


My AC has an intermittent issue where everything is fine, all of a sudden the air coming out is not hot anymore (or maybe it came on that way). The panel thinks cold air is being provided, but the fan on the outside unit is not spinning.

I had a company listed on the manufacturers website come out and look at everything on the outdoor unit and on the furnace. They saw no electrical issues, no refrigerant issues. Everything was working as it should. We were not able to get them to replicate the issue while they were there.

There were two techs. One said he thought the issue was probably because my capacitor was too big; however, the other one said he thought it was correct and it wasn't going over the max value (forget which value he said, I believe it something divided by or from the capacitance measurement). His rationale was that the capacitor was oversized and would cause the motor to overheat. He said there was rust on the fan motor and that this could be the reason why. The first guy called the office and someone told him he was right. The second tech said that the panel said it was correct; however, the first guy said that the chart on the panel is only for 440 not 220 and you need to divide (I did notice writing this up that the capacitor itself says 440V AC on it). The first tech said some other things which made me doubt him. My concern was that the capacitor is an easy thing to change and then bill for, and maybe it is not really needed?

Currently installed on the outdoor unit is a 75 uF capacitor. There is no bulging or discharge issue with the capacitor itself. This has always been there and I believe it is an OEM part (it's not a multi-option thing). The tech who wanted me to change, said it should be 35 uF. He also said it was a 3 ton model, but based off of the model number I believe the model-code maps to a 5 ton so that made me loose some confidence.

This thing is still under warranty so I said I wanted to check to see what the manufacturer said is correct - what shipped from the factory? Maybe the installers switched it up or the factory made a mistake? Seems unusual for it to be so off when no one has ever changed it. This unit is less than 5 years old and came with a new-construction home.

The manufacturer refused to tell me anything saying they don't troubleshoot problems and said I should contact one of the companies on "this list". The company I called was on that list. This doesn't seem like an opinion question or troubleshooting... there is either something standard, something in the factory record for my serial number, or at least a chart to calculate the correct capacitor based on some factors, right?

I would appreciate if anyone could either help me figure out from documentation what I need or tell me how I would go about taking in various factors to calculate the correct capacitor. Is 75uF generally way off? I have second unit that is slightly different model with a 45uF and he said that would be better with a 35uF as well.

PS - This is the follow up to my post about the AC not calling, where I tried to figure this out on my own. If you are so inclined, please feel free to let me know if this capacitor problem is or is not likely associated with this as well.

Model AC I have: Carrier CA13NA0600NG

which according to this manual page I found means:

  • CA13 = 13 SEER Air Conditioner with Puron Refrigerant
  • N = Electrical Supply 208/230-60-1
  • 060 = Nominal Capacity 060 = 5 Tons

The capacitor is 75/5 uF. There are a bunch of numbers on it, but the one I see twice with a barcode is HC98KA076. Here is a photo:

photo of the capacitor

UPDATE 1 - Additional Photos

Okay, It looks like they were looking at the label on the motor itself (see photo 2). The label says run cap: 75 mfd / 440 VAC it also clearly says 230V, 60hz... which would seem to imply that this motor is designed for this electrical system and the 440 is the maximum voltage as noted in the comments. I also checked the other unit's motor label, it clearly says run cap: 45 mfd / 370 .

Is it really as simple as the capacitor needs to match what the motor says? Does anything else in the system impact what should be there. Sounds like I dodged the bullet by not letting them change anything.

Photo 1: Confirm this is three terminal 75 + 5 as noted in comments:

photo of the capacitor showing terminals on the top

Photo 2: Photo of the label on the motor itself

photo showing run cap 75 uf

Photo 3: The Side label on the unit

photo of air conditioner unit label

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  • What did the manufacturer install?
    – keshlam
    Commented May 4 at 0:24
  • @keshlam - Not sure. This is what has been there since I took ownership of the house, 1st owner, and it was installed by the builder a few weeks prior. No one has ever come out to do maintenance or repairs- i.e., this is what was "installed" by the manufacturer or the installer. When I asked the manufacturer "what capacitor should have come with my unit from the factory" they responded they could not diagnose problems and I need to call a contractor... the more or less refused to answer even after confirming I wasn't looking for diagnosis, just what should be there.
    – HelpEric
    Commented May 4 at 0:29
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    Well, the Capacitor's voltage is NOT a reason to "divide by 2" - a capacitor has a value of capacitance, and it has a Maximum Voltage it's rated for. If you operate it below the maximum voltage the value does not change. The excess voltage rating is simply a safety factor, and may in some cases be required to be more than the supply voltage due to transients on startup and shutdown. Incidentally, that's not a 75 uF - its a 75uF and a 5 uF in the same can, and should have 3 terminals (sometimes 4, but two are joined)
    – Ecnerwal
    Commented May 4 at 2:10
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    Can you edit in a picture of "the chart on the panel?" Likely your best bet is to call a different company on the approved list and hope for more competent techs, given the manufacturer response. You might also drop them a line about the apparent incompetence of at least one of the "approved" techs that were sent (or they would have agreed) and your original installer if the "wrong size" one is correct.
    – Ecnerwal
    Commented May 4 at 2:14
  • @Ecnerwal For << Capacitor's voltage is NOT a reason to "divide by 2" >> He said it would have been 75uF if the line was 440 instead of 220...but I believe the model code means its only ever for regular residential.
    – HelpEric
    Commented May 4 at 17:46

1 Answer 1

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I would trust the label on the motor over the tech that's bad at following technical information.

Note that the motor label states 208-230V supply (not 230/460 dual voltage, just usual could be 240 single phase or 208 one phase of 3) and 75uF/440V capacitor, and you have the stated capacitor (and supply.) If swapping it out, replace with the same values.

The tech is talking out the wrong orifice, and is frankly incompetent to be doing the job they are in. It is exceedingly normal for motor capacitors to require rating considerably above the supply voltage.

More basically, the motor label is "manufacturer instructions" and code says you follow those.

One possibility with your symptoms would be that the compressor motor is fine, and the outside unit fan motor (which appears to be separate) is not running sometimes, so the compressor overheats and shuts down.

I'm a bit confused on the state of your warranty if you have to use their list of (not always competent, it seems) techs but the parts would be charged for on a unit supposedly under warranty that you're trying to keep in force. Probably weasely details of weasely warranty language, but anyway - I would lodge a complaint with the manufacturer that the tech sent from their list was demonstrably incompetent. I suppose you could also complain to the company in question if it's not just the two guys you were sent. That's a VERY basic thing to Dead Wrong about.

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  • << confused on the state of your warranty if you have to use their list >> No idea, Carrier is a major manufacturer, but you don't even open a warranty claim with them, they tell you to call your installer or an authorized company. This is what they actually state on their website: << Your local Carrier expert (dealer) can provide additional details on your coverage. Connecting with your local dealer is the fastest way to get your equipment running. >>
    – HelpEric
    Commented May 5 at 14:19

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