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Thread: Heat pump compressor runs ,has full charge of ref. will not push/pull gas.

  1. #1
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    Heat pump compressor runs ,has full charge of ref. will not push/pull gas.

    Found heat pump compressor runs , system has gas, compressor (scroll) is turning in the correct direction and is not broken. Further inspection found accumulator slogged with oil. Is this oil slogged accumulator the reason for no refrigerant pumping, ie no refrigerant getting past the oil slug back to compressor ,so, no gas back none out and we see no deflection on our high pressure or "true" suction access ports. Further , what caused the oil slug initially?

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  3. Likes townsend liked this post.
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    Unless the accumulator was completely full of oil (highly unlikely) it shouldn't have impeded flow. There is however an inlet screen on the inlet port of the accumulator that can become clogged. The same clogging can also plug up the oil return port in the accumulator J tube. Has this compressor been replaced a couple of times perhaps?

    Not all accumulators have an inlet screen.

    Quote Originally Posted by townsend View Post
    Found heat pump compressor runs , system has gas, compressor (scroll) is turning in the correct direction and is not broken. Further inspection found accumulator slogged with oil. Is this oil slogged accumulator the reason for no refrigerant pumping, ie no refrigerant getting past the oil slug back to compressor ,so, no gas back none out and we see no deflection on our high pressure or "true" suction access ports. Further , what caused the oil slug initially?

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    Discharge sh will tell.
    Ssh? Dsh? Pd?

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    This was its first change , however , the compressor (like the old one) will not pump refrigerant, it appears there is no gas getting back to the compressor so there is not head pressure developing. Also though, we see normal standing pressures (R410) on our; liquid line ,suction line and true suction access ports. Where the "true suction" access port goes directly into the "inlet" of the accumulator but we see no change in pressure with the compressor running ,Iam guessing a blocked or slogged accumulator. PS, we also see no head pressure change (maybe 5PSI). Just an FYI , this is my 40th year in Bus. and have never seen this before. It is also worth note that Iam at about the 47th Parrallell (sth NB) and it is chilly hear.

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    Perhaps , if we could develop any pressure, nothing at suction, nothing at head, it wont pump any refrigerant.

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    3 phase?

    If the accumulator was that plugged, you'd hear the compressor pull into a vacuum.

    Quote Originally Posted by townsend View Post
    Perhaps , if we could develop any pressure, nothing at suction, nothing at head, it wont pump any refrigerant.

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    crmont , I meant to make that point at the first , sorry, no it is single phase.

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    If the accumulator was that plugged, you'd hear the compressor pull into a vacuum

    Quote Originally Posted by townsend View Post
    crmont , I meant to make that point at the first , sorry, no it is single phase.

  11. #10
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    crmont, indeed but we are not seeing this back at the accesses which are all before the accumulator. We are running about 5FLA ( this is a 3 ton so with any load we should be at least 14-16 amps minimally. Mike

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    Triple check the start/run capacitor wiring and the S-R-C wiring at the compressor. Check the capacitors with the meter. Make sure they are labeled right.

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    You mean the suction service port is after the accumulator? Between the accumulator and the compressor?

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    No, the access ports are all "before" the accumulator, so, if there is "suction" developing at the compressor , there is no access to see it, I looked for but couldnt find a 3/4 inch "bronze on" saddle T to put between the comp. and accumulator, largest I found was 1/2 inch.

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    Does the compressor stop instantly or does it spin down?

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    crmont , first, thank you for taking your time with this, second I foolishly thought that there was going to be something silly and quick as an answer. So lets just give out "all" that I have at this point. About 2 years ago a licensed mechanic had inspected this machine and proclaimed the compressor failed. This mechanic (before he could make repairs) took ill and unfortunately passed away. So now to date his customer came to me , I checked his system , still had enough refrigerant for a condensed liquid standing pressure, checked the electricals (capacitor, windings, wiring, short circuits, etc. All looked OK so I started it up. Compressor starts fine but only drawing 5 amps and no change seen on my pressure gauges. I "assumed" my predecessor was correct and the compressor was failed (probably a broken shaft from the motor to the scroll was my guess) . I changed the compressor and of course weighed in a correct charge at that time. Started it up and TA DA , same thing! Bench tested old compressor and it seems to pump fine. rechecked the electrical , all good. I figured no gas getting back to the compressor it would run but not develop any head. It would seem that where I was seeing pressure at the "true suction" access port which is attached just before the inlet of the accumulator but could check on the other side for suction pressure we had a blockage. Next, I unsweated the connection from the accumulator to the compressor ( at the accumulator end) and put nitogen into the true suction access and got a large amount of oil pushed out, One of my techs was doing this , so I dont know how much came out but he said it was a lot.

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    You guessed it , it spins down.

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    Meant to say "could not" check pressures on compressor side of accumulator

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    Quote Originally Posted by townsend View Post
    I unsweated the connection from the accumulator to the compressor ( at the accumulator end) and put nitogen into the true suction access and got a large amount of oil pushed out
    The oil coming out would eliminate the possibility of a blockage in the accumulator.

    While the suction port was open, did your tech start the compressor and see of it pumped?

    If it did, you may have a reversing valve problem.

  20. #19
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    I had that thought but could realize how any thig there would create a situation where we see no pressure changes when the compressor runs. I was thinking perhaps there was a solid column of oil between the compressor and the outlet of the accumulator and with cold temps the compressor will not pull the oil ?

  21. #20
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    That accumulator would have to have 2-3 GALS of oil in it. The compressor holds a qt or 2!

    Is there a senior tech that can help you?

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