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Refrigeration question......

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  • Refrigeration question......

    I have a dehumidifier that has a small unit motor/pump.

    The pump is not working. When I investigated, I found that the 1/4" faston connections to the pump are corroded, and the wires leading to them have melted insulation. It has an over-temperature cutoff, which is outside the case, adjacent to the connections.

    The pump case does not look in any way overheated.

    But obviously there is a problem.

    The question is whether the issue is due to the corrosion making bad connections, or due to the pump itself overheating. I suspect the cutoff would have shut it down well before melting wires if it were the motor..

    Other info:

    The motor needed a new capacitor a couple years ago, the old one opened up. After replacement, it worked fine. That replacement cap is fine still.

    I can fix the wire problem, but prefer not to take the trouble if the motor is likely to be bad.


    Is it fairly common to have corroded connections in an otherwise working unit? Being a dehumidifier, there is always water around it, so it seems reasonable.

    Does the melted insulation suggest anything past the lousy connections?

    Can these motors be effectively measured in any way that indicates damage? I can measure resistance, insulation to case, etc. I found no issues so far with what I would consider reasonable tests..

    It's a pain to reassemble to working condition just for a test, and there is a broken standoff for the relay PWB, for which the glue is drying now, and I'd rather not assemble the unit for a test of function until later.

    I'd also rather cut my losses if there is an obvious symptom of failure.. I can replace it, but I prefer to fix if that is reasonable (a new pump is NOT reasonable). But I know little about refrigeration type unit pumps and their common failure symptoms.

    CNC machines only go through the motions

  • #2
    The corrosion created high resistance in the connections and therefore overheated the wires.
    12" x 35" Logan 2557V lathe
    Index "Super 55" mill
    18" Vectrax vertical bandsaw
    7" x 10" Vectrax mitering bandsaw
    24" State disc sander


    • #3
      One of the best ways of testing a motor is to measure the running current and compare it to the nameplate spec. You need a clamp-on ammeter, but H.F. carries them, starting at $15.00:


      • #4
        Got plenty of ammeters, and agree that corrosion may be the culprit..... both for not running, and for heating of wires,

        What I do NOT know is if the corrosion issue is common on these things, and whether or not it suggests some other problem. I just do not deal with these much, and do not know the common symptoms etc. That is the basic issue.

        I can handle the repair, and since it was working a day or two back, it may well not be anything more than the corrosion/bad connection. But, since refrigeration is not my thing, I thought I would ask before sinking work into the unit.
        Last edited by J Tiers; 07-10-2021, 07:51 PM.
        CNC machines only go through the motions


        • #5
          Originally posted by J Tiers View Post
          ...What I do NOT know is if the corrosion issue is common on these things...
          Apply dielectric grease to the connections after cleaning and before reconnecting.
          12" x 35" Logan 2557V lathe
          Index "Super 55" mill
          18" Vectrax vertical bandsaw
          7" x 10" Vectrax mitering bandsaw
          24" State disc sander


          • #6
            Slap some temporary jumpers on and see if it goes back to working fine. If it does, put in the extra work to make permanent connections.


            • #7
              J Tiers,

              When you say pump, Are you talking about the compressor, or is there a pump to remove water from the dehumidifier? I have a free standing one in my basement that has a compressor and a fan but no pump, it catches the condensate in a bucket built into the bottom and we have to dump it when if fills up and shuts off the unit.

              If the compressor leads are at issue I like EKretz's suggestion of jumpers and apply power just to see if it runs, only has to be a few seconds. The compressor is a reciprocation or scroll motor that moves the refrigerant gas and compresses it from low to high pressure before it moves on to condense into a liquid before cooling to remove the moisture in the air which then goes through a defrost cycle and then starts the cycle over again.

              Click image for larger version

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              Probably TMI, but maybe it will help other readers.

              Mr fixit for the family


              • #8
                Finally got one of the connections off the pump. The post on the pump, and the "faston" used for the connection are both rusted (weird, since I don't think both are steel). The usual round ost with a small tab welded on to fit the faston.

                I am not sure what order things happened... the 3rd post, for the capacitor wire, is not rusted, suggesting that the heat occurred when the original cap failed, and that the heat damaged the plating so that the two main motor lead connections corroded.

                Do these things typically short to the case if they do overheat? No sign of that so far.

                I don't have a crimper for flag type fastons, so I may have to modify the cap assembly that covers the terminals, and holds down the overtemp sensor, to take straight terminals.

                "Pump" is the unit compressor, yes. That's what we called them at a prior employer. (we designed some stuff for them, but did not repair them, so no idea on symptoms).

                I'll hit it again later today.
                Last edited by J Tiers; 07-11-2021, 01:09 AM.
                CNC machines only go through the motions


                • #9
                  Compressor manufacturers list winding resistances by model numbers usually in repair manuals. Service people refer to these as a guide. You should know start from run winding. Measure largest resistance across two of the three compressor terminals. This is start and run in series. The third terminal is common. Measure common to each of the other two. The larger resistance is start and the remaining is run. Usually the terminals are round with a moulded connector to fit over all three. Corrosion is fairly common. About all you can do is clean terminals and give it another go if the winding resistances are within specs. Meg terminals to copper refrig. line with no more than 500 volt megger. About 100 Meg is minium and infinity is better. Many times wires melt from sticking current type start relay when it doesn't come off start winding. I only mention all this because like many on here you want to repair things rather than toss them on the junk heap. In a way we are all relics that live in a throw away world and we still want to fix things when the economics are against it. You may waste a few hours and it will be for nothing. Good luck.


                  • #10
                    If it’s a shop dehumidifier the condensate can also be somewhat chemically contaminated depending on what’s airborne to add to the mysterious case of the dehumidifier, sound like an old columbo film .


                    • #11
                      Those compressor connectors are a common failure, even with whole house AC units. For larger compressors they make a repair kit which consists of screw on lugs to attach to the compressor terminals, the original connector (on the wire harness) is cut off. Basically, instead of a crimp connector end they use a lug that bolts onto the pin coming out of the compressor. Like I said, its a common failure with compressors in whole house AC units, not sure about small compressors the currents are tiny so it may not happen as often (although it sure appears it happened to you).

                      Here is a example of a repair kit for larger compressors, such as house AC units, but the concept is the same

                      Overtemp cutoffs are typically internal to the compressor. On those tiny compressors they commonly have the run/start relay incorporated right into the plug that mates with the compressor, this is how your typical household refrigerator is configured. The run/start relay is typically a potential type relay, actuated when the voltage drop to the start winding decreases (same type relay commonly used in home brew phase converters for automatic starting)

                      Worth noting that the pins extending out of the compressor have seals where they pass thru to the internals of the compressor. Its not uncommon if those pins get very hot from bad connections that the seal fails and freon is discharged violently as a result. I note this to discourage soldering wires or such directly to the compressor terminals/pins, there is 100+PSI on the other end of those pins.

                      A commercial refrigeration supply house would probably have a repair kit for your compressor terminals. Your typical heating/air conditioning supply house does not carry supplies for tiny refrig units like this, you need a refrigeration supply house. Be advised, these supply houses often stop DIY'ers right at the door and will not sell to them. In any event, do not refer to it as a "pump"if going to a supply house, that will trigger a huge red flag immediately.

                      Good luck, it should be able to be repaired.
                      Last edited by Sparky_NY; 07-11-2021, 07:35 AM.


                      • #12
                        I recall a funny incident with a clamp on meter. A qualified electrician who should have known better bought a cheap clamp on meter from Lidl and tried it out on the power cable to one of the mills, single phase 230V. It did not seem to work, so I suggested that he tried it on a single conductor at a time rather than positive, neutral and earth together.


                        • #13
                          No one-piece connector here, the round pins have welded-on flat pieces to convert them to faston terminal compatibility. I've seen a LOT of similar units.

                          We did consulting for a local A/C manufacturer, and all the ones we dealt with had faston compatible terminals, although the unit compressors were several times larger. (We designed some special soft start units for them, among other things, special because the customer required low current starts.)

                          I am aware of the "to the trade only" routine. They won't have anything I need anyhow.

                          CNC machines only go through the motions


                          • #14
                            Originally posted by J Tiers View Post
                            I am aware of the "to the trade only" routine. They won't have anything I need anyhow.
                            You don't want to spend $82 for 3 wires & connectors either (

                            "Faston" - generically known as spade connectors.


                            • #15
                              Very common 1/4 spade connector in HVAC. Sometimes you go into an older control panel and half of them are cracked. They need about 10 lbs of force to pull them off with needle nosed pliers. If not they need to be replaced. The ones for compressor terminals are a heavy duty version. At times the spades on the compressor are rusted off. There are repair terminals that tighten with an allen wrench.