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  1. #1
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    Compressor running with a bad capacitor?

    I saw something strange yesterday that I need an explanation for. I was on a service call for cooling on a Lennox 10ACC-042-230-02 unit made in 2008. Main problem was a bad capacitor on the indoor fan motor. I was certainly glad I didn't have to replace the motor in a 110 degree attic! After I got the system up and running and checked the operation of the indoor unit I went outside and checked the condenser. When I opened up the unit I saw a familiar sight, the dual capacitor was completely covered in rust, to the point where you could no longer read the ratings printed on it. Why is it always like this with the caps Lennox uses?
    Luckily for me a previous tech marked the panel with the ratings, 45-5 370 volt. Someone put a single 5 microfarad capacitor on the fan motor, I assume due to a failure on the dual capacitor. When I tested the dual capacitor both sides were dead!! The compressor was running! The unit was equipped with a Supco two wire hard start kit, was this cheap hard start doing the job of the dual capacitor?

  2. #2
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    A duel cap is exactly that 2 caps. One is for the fan motor one for the comp. In your case yes the Supco was running the comp. Replace the Supco with a 45/440 if thats what it takes.

    never trust what someone else wrote on the cabinet, verify. Contact the supply house and have them look it up.

    A good read on Motors & Capacitors:
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  3. #3
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    Quote Originally Posted by pecmsg View Post
    A duel cap is exactly that 2 caps. One is for the fan motor one for the comp. In your case yes the Supco was running the comp. Replace the Supco with a 45/440 if thats what it takes.

    never trust what someone else wrote on the cabinet, verify. Contact the supply house and have them look it up.

    A good read on Motors & Capacitors:
    Thank you for the reply and recommended reading. I understand the purpose of the dual capacitor and I figured that the Supco was responsible for the compressor being operational. I just have never been this happen before, I think I remember finding compressors not running with a bad capacitor and hard start equipped.

    It's definitely time for me to refocus on A/C work for the short cooling season we have here in NY. I have had nothing but hydronics and combustion analysis on my mind for months now.

    I love this site, very knowledgeable members here. Great to learn from. 11 years in the field and I will never stop learning until they pry the nut driver from my cold dead hands!😀

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  5. #4
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    Quote Originally Posted by HVAC_Dave_NY View Post
    Lennox 10ACC-042-230-02 unit made in 2008.
    Luckily for me a previous tech marked the panel with the ratings, 45-5 370 volt.
    As previously stated by "pecmsg", never trust what it written on the cap.

    Lennox parts is showing this should be a 40 + 7.5 MFD, 440volt capacitor. Assuming the original compressor and fan motor are still in the unit.
    Instead of learning the tricks of the trade, learn the trade.

  6. #5
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    Quote Originally Posted by rundawg View Post
    As previously stated by "pecmsg", never trust what it written on the cap.

    Lennox parts is showing this should be a 40 + 7.5 MFD, 440volt capacitor. Assuming the original compressor and fan motor are still in the unit.
    Fan motor wasn't original and I made sure that it requires a 5 microfarad. I should have checked the compressor. I installed a 45/5 440 volt.

    Some guys say it's good to put a higher microfarad capacitor in, but I always like to install what the manufacturers specifications require. Except I always use 440 volt.

    Any thoughts on effects of using a higher microfarad capacitor? I've heard guys say "it's old, it's needs a bigger one." Lol.

  7. #6
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    Never change the MF rating.
    Due to the cheapening of parts I only stock 440 vac caps.

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  9. #7
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    Does a higher microfarad capacitor have the potential to damage the start windings?

  10. #8
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    Yes

  11. #9
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    Caps do their job by providing a phase shifting effect that needs to match the amount of phase shift built into the start winding. Too high or too low of a phase shift leads to excessive slip against the start winding, which causes it to heat up and draw more amperage, which accelerates system wear. As an aside, this sort of thing is accounted for in commercial static phase converters by switching banks of capacitors in and out of the circuit as the load changes. Don't know why I thought of that just now, was just interesting to me.

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  13. #10
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    Quote Originally Posted by rjk_cmh View Post
    Caps do their job by providing a phase shifting effect that needs to match the amount of phase shift built into the start winding. Too high or too low of a phase shift leads to excessive slip against the start winding, which causes it to heat up and draw more amperage, which accelerates system wear. As an aside, this sort of thing is accounted for in commercial static phase converters by switching banks of capacitors in and out of the circuit as the load changes. Don't know why I thought of that just now, was just interesting to me.
    Excellent explanation. Thank you sir!

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