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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 945
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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What causes a semi hermetic with out a receiver to pump back

Customer Question

what causes a semi hermetic with out a receiver to pump back down?
Submitted: 2 years ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 2 years ago.

Hi I'm Brian and I'm here to help!

Can you clarify your question a little bit more please? Add as much detail as you can e.g. system type, application, size etc...



Customer: replied 2 years ago.
When recharging the system my high side is 150 psi and my low side hits 50 psi it starts to pump down on the low side the the compressor just shuts down, I think it low pressure switch.
Expert:  Brian HVAC Guy replied 2 years ago.

That would be the most probable cause. Since you shouldn't add refrigerant at a fast enough rate to keep the low pressure switch closed, otherwise you'll be adding straight liquid and possibly washing the oil off the bearings of the compressor. This certainly can be a nuisance. What type of system are you working on and how many horsepower is the semi-hermetic compressor? If you can give me the model number, I can look up the literature and perhaps give some better advice.


Customer: replied 2 years ago.
It's a carrier
S# *****
Expert:  Brian HVAC Guy replied 2 years ago.

So this is an 80hp open drive compressor?

Customer: replied 2 years ago.
what can be cause of the problem
Customer: replied 2 years ago.
Did I run out of money time?
Expert:  Brian HVAC Guy replied 2 years ago.

And you're charging the system from flat empty as in from evacuation up through full charge? To answer your question properly I really need to get an understanding of what you're working on. Is this an R22 refrigeration unit, ice machine, etc...? That's a large compressor and will have a very large operating charge in any system it's used in. I'm sure there are operating safeties including a low pressure switch. In a system that large what I would normally do is 1) if there is a liquid line solenoid valve, bypass the control and power it up so the full system was open. 2) disable the compressor motor from starting and 3) Add a liquid charge into the high side until the pressures equalized. 4) Remove the bypass for the liquid solenoid valve and then finally start the compressor. This method gets a large amount of refrigerant in the system. Hopefully to the point where it won't trip out on suction pressure safety. Then all that needs done is to top the charge up to full operating charge. Of course the compressor has to be fully loaded to get the correct charge in.

In short, I would have to venture a theory from what you've told me that yes, it's tripping on its suction pressure safety. More info is necessary to make a sure call on that though.

Let me know if I can clear anything up. Send me the info requested on the application and it will help me understand much better.



Expert:  Brian HVAC Guy replied 2 years ago.

And FYI, we don't have time based billing anymore in this category! We have as much time as necessary.

Customer: replied 2 years ago.
Great thanks, ***** ***** back to you.
Expert:  Brian HVAC Guy replied 2 years ago.

Very good then. Good luck with it and be safe!

Best regards,