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

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  • #31
    You might like to check out this PM thread on relubing an oilite bearing:

    https://www.practicalmachinist.com/v...earing-213850/

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    • #32
      Originally posted by PStechPaul View Post
      I notice that the diagram shows an oil charge of 12 fluid ounces. I've never changed the oil or the refrigerant, and I assume both are for the compressor.
      Don't ever mess with the refrigerant charge in these small units. When the factory charges them they pinch close the charge port and solder it closed for good measure. It is almost never the refrigerant. The old refrigerant systems that used Freon and mineral oil were unbelievably bullet proof. There's an interesting story on this - there's a lighthouse on the Oregon Coast nicknamed "Terrible Tilly" It was decommissioned in the mid 1950s the government was tired of people dying or going insane when being posted there. In the mid 1970's some nutcase with more money than brains bought it and owned it for a couple years before selling it to someone else even nuttier than he was. Anyway he landed on the thing with a helicopter in 1973 and supplies and a generator. The story goes that when they plugged in the refrigerator left there from 20 years earlier and turned it on it still ran. This in a building that periodically got flooded with salt water. Here's a pic of the thing on a NICE day....I'd like to see an A/C unit or refrigerator manufactured today survive THAT for 20 years....

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      • #33
        As a kid growing up in the '50s, we always had the same refrigerator, which I think was a "Hotpoint" brand. I think my parents bought it before I was born (1949). After several moves it was still in my parents' house when they died (1983 and 1996). The only maintenance needed was a new gasket and replacement of the freezer drip tray, and my father made one from plexiglass. After kicking my brother out and buying the house back from the courts in 2003, the refrigerator was horribly filthy and smelly after having been left with food in it and without power for a year or so. I had a contractor fix damages to the house, and planned to junk the old fridge, but the contractor said they had cleaned it up and it still worked. But I had my own refrigerator in my house so I told them to get rid of it. So that was about 55 years of continuous use.

        Looks like maybe I should have kept it. Here is perhaps the identical 1948 model, unrestored, for $4800!



        Last edited by PStechPaul; 08-06-2020, 04:36 PM.
        http://pauleschoen.com/pix/PM08_P76_P54.png
        Paul , P S Technology, Inc. and MrTibbs
        USA Maryland 21030

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        • #34
          I took apart the bearing retainer for the troublesome end:

          Click image for larger version

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          The bore does not appear to be badly scored, but the armature shaft definitely shows signs of scoring. But it turns pretty smoothly after a quick cleaning, so I think I'll try using some lightly abrasive Scotch-brite The bearing appears to be steel, so I think just some good light oil should suffice. I don't know if I should try to add any sort of packing as was present in the original unit. I'm not sure how it would help keep it lubricated if soaked with oil, but perhaps the axial motion of the shaft against the springs causes oil to squeeze out onto the shaft.
          Click image for larger version

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          This is the other end bell, which seems to be OK, although the packing is dry and falling apart.
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          The stator looks pretty good:
          Click image for larger version

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          Click image for larger version

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

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          • #35
            Well, I cleaned up the various parts of this A/C and I used the lathe to smooth out the rotor shaft ridges. Then I put the motor back together, figured out how to connect the wires to the switch and run capacitor, and gave it a try. It ran OK in high speed, but I found the pow speed winding was open (actually about 14k). I took it apart again and carefully examined the stator windings, but didn't see any sign of damage or overheating, although there was what appeared to be some varnish on the laminations and some of them appeared to be separated a bit. I cleaned that up, reassembled, and it ran very smoothly on high speed. It also ran for a few seconds on low speed before stopping. Perhaps there is a resettable thermal overload in the windings that has become intermittent?

            At this point I think I'll put it all back together and just use it on high speed when I need it. This past week has been cooler, 85-90F, and I'm enjoying fresh air with an open patio door and an oscillating fan. I am considering making a single phase VFD to run the fan with variable speed, but that's a bigger project than I want to tackle right now. However, I'm considering making a cirvcuit which applies every other half-wave of 120 VAC, effectively providing 60 VAC at 30 Hz. Shouldn't be difficult, and might be useful for other applications.
            http://pauleschoen.com/pix/PM08_P76_P54.png
            Paul , P S Technology, Inc. and MrTibbs
            USA Maryland 21030

            Comment


            • #36
              Electrolytics can be had in many different tolerances. Some can be as tight as 5% or even 2% or 1%. The cheap ones for appliances will have much larger tolerances. This keeps the price down by making almost every one that comes off the assembly line within tolerance.



              Originally posted by Jim Stewart View Post

              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
              Paul A.
              SE Texas

              Make it fit.
              You can't win and there IS a penalty for trying!

              Comment


              • #37
                I remember when I was younger and got a bargain AC unit for $10 or $15. It needed some work, but it kept my wife and I cool for several summers. I was in the Army at the time and money was tight. IIRC, the capacitor was one of the items I had to replace.

                I say go for it.



                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!
                Paul A.
                SE Texas

                Make it fit.
                You can't win and there IS a penalty for trying!

                Comment


                • #38
                  I thought a bit more about how to make an easy 30 Hz waveform for low speed. If I use a simple series SCR or TRIAC switch, I would have to turn on a full cycle and then turn off a full cycle, which would probably be noisy. But it is simple enough that I might try it. The same thing can be done with a full wave bridge and a single SCR.

                  Another way would be a full wave bridge to get a rectified AC signal, and then four SCRs in a bridge, which could apply every other half wave to the load which would be something like a modified sine wave at 30 Hz. But that requires the full rectifier bridge as well as four SCRs that need to be triggered.

                  Going that far, I might as well just rectify the AC into a bus link capacitor and use four MOSFETs or IGBTs as a proper VFD. I could then use a simple modified sine wave or go with a proper high frequency PWM.

                  I just tried using a Variac, and the motor will actually start on 40 VAC and run at 20 VAC. I wonder if just a step-down transformer or phase angle variable control would work?
                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

                  Comment


                  • #39
                    Originally posted by tlfamm View Post
                    You might like to check out this PM thread on relubing an oilite bearing:

                    https://www.practicalmachinist.com/v...earing-213850/
                    I was taught to soak oil bearings in hot oil overnight, just heat up, drop in bearings, let cool and soak overnight. Always worked well for me.

                    Comment


                    • #40
                      I think perhaps it would be best to first soak them in solvent, like brake or carb cleaner, maybe also in an ultrasonic cleaner. Then thoroughly dry, heat, and drop into oil. But I found that these are actually steel. The motor does spin smoothly and quietly now, without the fan and blower.

                      [edit] It is back together and blowing cold air on high fan. I'm not going to fool with making it run slow - maybe later.

                      [edit2] After running a while, now it seems that the low speed fan is working again. So, probably a thermal overload that finally reset.
                      Last edited by PStechPaul; 08-10-2020, 12:59 AM.
                      http://pauleschoen.com/pix/PM08_P76_P54.png
                      Paul , P S Technology, Inc. and MrTibbs
                      USA Maryland 21030

                      Comment

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