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  1. #1
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    Pumping down scroll compressors

    I have to move three condensers for a customer next week. I haven’t looked if they are scroll compressors, but they are less than 3 years old. I worry about damaging a scroll compressor by pumping it down and am planning on evacuating all three systems. Am I being too cautious?


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  2. #2
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    Don’t run them into a vacuum and you will be just fine. The IPR may open before that point anyway. Good luck.

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  4. #3
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    Quote Originally Posted by knave View Post
    Don’t run them into a vacuum and you will be just fine. The IPR may open before that point anyway. Good luck.
    I never ran into a pump down issue until just yesterday actually. It was a 5 year old Goodman I think it was a scroll. On a pump down obviously I close my discharge, shortly after it's not pumping down and seems to be in equilibrium. Is that what the IPR does? What is IPR?

  5. #4
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    Never had an issue pumping down a scroll; just leave enough positive pressure in it to keep you out of the green. The scrolls rattle a bit as you near the end. Open the electrical panel so you can push in the contactor if it has a low pressure switch.

    The Internal Pressure Relief valve should not open unless the pressure differential becomes quite great - on the order of 500 or more psi on Copelands, if I recall correctly. If it opens during a pump down, it is far too weak and failed.
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  7. #5
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    Some manufacturers are using small diameter condenser tubing which makes pump down very difficult if not entirely impossible.

    I would caution about partial pump downs on R410A systems. Since its an azeotropic mix you never know in what relation you actually pumped down each component. Same is valid for leaks. Therefore I alway recover entirely and never have an issue.

  8. #6
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    I would also caution on pushing in a contactor.

    Seen three blow up over the past five years.

    All 460, so maybe okay on a resi thread.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

  9. #7
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    Yoo can pump a scroll down.Dont pump it into a vacuum.scrolls pump down all the time on refrigeration units.

  10. #8
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    Some scrolls have another internal protector that works off compression ratio. When it exceeds 16:1 or even higher I can’t remember, the scroll plate unloads.

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  12. #9
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    Quote Originally Posted by Hvac talker View Post
    I would caution about partial pump downs on R410A systems. Since its an azeotropic mix you never know in what relation you actually pumped down each component.
    Please
    post Documents supporting this statement!

  13. #10
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    I will also add this info.You need to have your high side gauge hooked up.If you go off on high head before you get pumped down ,your condenser may not be big enough to hold the complete charge.This is not usually a problem with a line set run of 25 feet or less.If you have a long line run, you may only pump down to 10-20 PSI ,then head pressure is over 300.your condenser may not be big enough to hold the extra charge.if you are stuck at a low pressure of say 15-20 PSI,and wont pump down any further, your condenser is probably full.You have to recover the rest.Some residential units have High Pressure controls, some don't.Anyway,If you can't pump down any further .Recover the rest.If you pup down to 0-2 PSI,your good to go!!!

  14. #11
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    Quote Originally Posted by Gleng View Post
    I will also add this info.You need to have your high side gauge hooked up.If you go off on high head before you get pumped down ,your condenser may not be big enough to hold the complete charge.This is not usually a problem with a line set run of 25 feet or less.If you have a long line run, you may only pump down to 10-20 PSI ,then head pressure is over 300.your condenser may not be big enough to hold the extra charge.if you are stuck at a low pressure of say 15-20 PSI,and wont pump down any further, your condenser is probably full.You have to recover the rest.Some residential units have High Pressure controls, some don't.Anyway,If you can't pump down any further .Recover the rest.If you pup down to 0-2 PSI,your good to go!!!
    High side gauge does no good unless you can get it on the inside of the condenser. If you put it on the service valve, its the same as it being on the suction.

    You can pump a scroll down


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  16. #12
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    I was not aware the relief was based on pressure ratio. I had always just figured those little scrolls had no balls. I still believe the later to be true but thanks for the info.


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  17. #13
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    Quote Originally Posted by Hvac talker View Post
    Some manufacturers are using small diameter condenser tubing which makes pump down very difficult if not entirely impossible.

    I would caution about partial pump downs on R410A systems. Since its an azeotropic mix you never know in what relation you actually pumped down each component. Same is valid for leaks. Therefore I alway recover entirely and never have an issue.
    410A has almost no glide. I wouldn’t worry at all about pumping it down or topping it off.

    Scrolls pump down just fine, they are common on pump down refrigeration systems. Sometimes they rattle a bit as the pressure gets close to zero.

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