Engine Size: 2.5
Refrigerant Type: R12
I got a lot of good advice from this site on how to proceed on getting an operating AC on my 1983 Porsche 944 (under the topic "leak testing an empty system"). Basically, the majority of the advice based on the details I provided was to replace the drier and refill with R12. I am now am considering the refill procedure and thought that a new topic was in order. My questions are:
(1) When I replace the drier, I will measure the amount of oil in it and add that to the new drier. However, I do not know how much oil might have been lost during the removal of the old R12. Any thoughts on how much (if any) additional I should add to cover that? Is the precise amount of oil in the system critical?
(2) I have 12oz cans of R12; should the can be upside down during the refill so liquid enters the low side, or should the can be upright so vapor enters?
(3) The system has a low pressure cut-out switch. I assume I should bypass this during the fill procedure so the compressor is running right from the beginning of the refill. Is this correct?
Thanks for any help!
1) You will need to drill a small hole in the bottom of the dryer, and let it drain overnight. This will not get 100% of the oil out of it - some oil remains trapped by the surface area of the desicant grain. Adding back the volume you have drained plus additional oil is the standard practice. If no oil drains from the dryer, add back two ounces of oil. If you drain more than two ounces of oil from the dryer, refill with the same quantity as drained plus a half ounce for trapped oil. Don't forget to add the UV dye at this point too.
1.1) After adding the proper oil charge, you need to evacuate the system. This is the first leak test as well. Once you have evacuated the system, close the manifold valves & wait an hour. If the vacuum had dropped by more than 5 inches, you probably have a leak. Vacuum again, and re-test.
2) Hopefully you have a 4-port manifold, or have converted yours (check the FAQ's for a step-by-step). If the system holds vacuum, you are ready to charge. With the can tapped, and the valve off you can evacuate the charging hose.
2.1) You will be adding the first can as a liquid through the HIGH side with the engine stopped. This allows a partial fill before starting the compressor, to help move oil back to the compressor. You do this through the high side to avoid washing the oil out of the compressor with liquid refrigerant. Once you have as much of the first can in as it will take, you can close the high side valve. Once you are sure that both manifold valves are closed, you can start the engine, and begin charging Vapor through the LOW side. This is how you will complete the charging process.
3) At NO time should you disable the low pressure switch, or "jump" the compressor. Running the compressor for fifteen minutes with no refrigerant to return oil to the compressor while you add vapor to the suction side sells a lot of compressors. That switch is there for a reason.
Good luck with your project.
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
Thanks! This is what I need to know. The reason I mentioned bipassing the low pressure switch is that the recharge procedure under the "Automotive airconditioning procedures" section of this forum suggested it if the compressor was not running. After adding a can to the high side (engine off), will the pressure now be high enough to activate the clutch, or doesn't this matter? I read somewhere that it may be necessary to warm the freon can to get transfer to the system. In your experience, will this be necessary? Finally, is idle speed OK during the fill, or does the engine have to be run at a higher rpm (say 2,000 that I read somewhere)?
Thanks a lot; initially missed your reply at the end of my questions. I think you answered the remaining issues! I am ready to give it a try.
Sorry, I forgot one other question. I have a TEK MATE leak detector. How does this compare to the UV dye for finding leaks? Given that I have the detector, I was wondering if I should still add the dye.
I would add the UV dye as it does no harm and can aid in "future" leak detection..Hope this helps..
Freedoms just another word for nothing left to lose
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