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OT: Old air conditioner - needs dual run capacitor 17.5/7.5 330V

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  • OT: Old air conditioner - needs dual run capacitor 17.5/7.5 330V

    I have an old (1970s) "portable" air conditioner (it has a handle) that I bought from a friend for $35 around 1979. It has worked pretty well during the times I had it installed. I haven't used it for about 5 years but today it hit 97 degrees and I felt it was time to use it. It probably weighs 50-60 pounds and it was about the limit I could handle with my back being supported by rods and screws, but I hefted it into the window and got it running. It took about an hour to bring the temperature in the bedroom down from 89 to 82 degrees, and humidity from 65% to 55%, and it felt good. Then I heard the compressor kick out and just the fan was running. But a few minutes later, it tried to start, and kept tripping the thermal overload. Even after turning it off for 20 minutes and trying again, it did the same thing.



    So I took the cover off:



    Wiring diagram:



    I pulled the capacitor and measured it. One side was OK, reading about 7 uF. But the other side was basically shorted. And it was fairly hot:



    Should be a pretty simple repair, but I can't find that exact value. Home Depot has a 15/5 uF capacitor for $11, but it's a round can 2" diameter and 4" long. The original is 1-3/4" x 2-3/4" x 5-1/4". It should fit.

    http://www.homedepot.com/p/TradePro-...5440/300839430

    I also found a 15/5 uF flat can for $4.96 and a 20/5 for $5.49.

    http://www.hvacpartsource.com/DUAL_R...ORS_s/1942.htm

    I think any of these will be OK. I like the price and selection from hvacpartssource.com, but there will be shipping costs. I can order the HD part to be shipped to store free, but delivery would be at least June 19. I probably have a couple of single capacitors of appropriate value, but it would be an ugly kludge.

    [edit] Also found a 20/5 oval capacitor at HD, 2" x 2.5" x 4", $11:
    http://www.homedepot.com/p/TradePro-...5440/300839440

    and 25/7.5, 2" dia, 4" long, $14:
    http://www.homedepot.com/p/TradePro-...5440/300839425
    Last edited by PStechPaul; 06-14-2017, 12:04 AM. Reason: links
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

  • #2
    If it were me I would divide and conquer. Find individual replacements for each value and tie wrap them together.
    Location: Long Island, N.Y.

    Comment


    • #3
      It just has to be reasonably close. These caps are not terribly high tolerance to begin with.

      Comment


      • #4
        Graingers, Johnstone Supply or any HVAC supplier would have a suitable replacement. In this heat why would you be screwing around with a mail order supplier?

        Comment


        • #5
          Originally posted by macona View Post
          It just has to be reasonably close. These caps are not terribly high tolerance to begin with.
          Seems like tolerance isn't usually listed on electrolytic caps, but last time I looked into the issue I found that standard tolerance was -20% to +100%. That was 20-25 years ago, so probably applies to your '70s capacitor.

          -js
          There are no stupid questions. But there are lots of stupid answers. This is the internet.

          Location: SF Bay Area

          Comment


          • #6
            But those are motor run caps, possibly 10% tolerance.

            The fan might be OK at 5, although that is 60% of nominal, but the compressor may want better due to the load on it.
            1601

            Keep eye on ball.
            Hashim Khan

            Comment


            • #7
              I question that they are run caps, more likely start caps. The schematic even shows the cap connected to the "S" terminal on the hermetic compressor. (start winding)

              The 25/7.5 home depot cap is a good choice.

              Comment


              • #8
                It's a permanent split capacitor compressor motor. Both are run caps. You could leave the 7 which is for the fan and just add the 27 if you have room.

                Comment


                • #9
                  I found a 7.5 uF 280 VAC capacitor and several 12 uF 280 VAC capacitors. I installed the 7.5 and one of the 12 and it runs fine. The 7.5 uF can read 7.0 uF and the 12.0 uF cans both read very close to 12.0. The motors must be PSC type. I'm waiting for the room to cool down before I do a better job of installing the cans and closing it up. It's ugly as it is now:

                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

                  Comment


                  • #10
                    With the low value of 12 in place of 17, it may run hotter than it should. Torque will be low, which is bad for compressors.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      I applaud people fixing things instead of just dumping them. However an air conditioner of this vintage I would not have saved. Air conditioners back then were big, heavy and sucked energy. Huge advances have been made in this area and a single room 5000 btu airconditioner is like $129 and weighs 35 lb. using just 4 amps at 120 vac. Just think of your back savings alone!

                      Comment


                      • #12
                        That is so.

                        But he HAS that heavy and hungry unit, and does not have the new unit. Thee is much to be said for using what you have.

                        Replacing it may become not an option, but a necessity at a later time if it fails, but meantime, it cools rooms.
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #13
                          Originally posted by garyhlucas View Post
                          I applaud people fixing things instead of just dumping them. However an air conditioner of this vintage I would not have saved. Air conditioners back then were big, heavy and sucked energy. Huge advances have been made in this area and a single room 5000 btu airconditioner is like $129 and weighs 35 lb. using just 4 amps at 120 vac. Just think of your back savings alone!
                          Problem with those units,and I have had several,is they contain digital electronic items that go poof and can't be replaced.So is it more efficient to keep the old school one running,or expend possibly several times the energy loss building a new "modern" unit every couple years?Just sayin.
                          I just need one more tool,just one!

                          Comment


                          • #14
                            Another thing to consider is that I will probably only use this A/C occasionally, when it's unusually and oppressively hot and humid. It would make much more difference if I would use it more often, or if it were larger and I used it to cool more rooms, or the whole house.

                            It seems to me that the smaller capacitor would draw less current, but that also depends on the BEMF of the motor and the characteristics of the secondary winding. It starts and runs well, so I don't think it will be a problem. I have a "Kill-A-Watt" that I will use to see just how much power it's using.

                            The only small A/C in stock at Home Depot is $139, and weighs 47 pounds.
                            http://www.homedepot.com/p/GE-5-000-...05LV/206685276

                            Walmart has one for $112 that weighs 41.5 lb:
                            https://www.walmart.com/ip/Haier-5-0...XCR-L/49229367

                            And this one, with a remote, about 42 lb, for $134:
                            https://www.walmart.com/ip/Haier-5-0...XCR-L/49229370

                            I can't find one that is only 35 pounds, but not all models list the weight.
                            http://pauleschoen.com/pix/PM08_P76_P54.png
                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030

                            Comment


                            • #15
                              Originally posted by reggie_obe View Post
                              Graingers, Johnstone Supply or any HVAC supplier would have a suitable replacement. In this heat why would you be screwing around with a mail order supplier?
                              You would think, but I only managed to find ONE 17.5/7.5 dual run capacitor (round) listed anywhere- and it was rated for 440 volts. Yeah, it would work just fine but I would really hate to see how much they wanted for it! I would have just gotten the two separate caps and been done with it.

                              When working with really old stuff with outdated parts, you can't expect everyone to have it in stock.

                              Comment

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