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How do I decide how much oil?

befuddled on Wed July 16, 2008 9:15 AM User is offline

Year: 2000
Make: Nissan
Model: MAxima
Engine Size: 3.8
Refrigerant Type: 134
Ambient Temp: 75
Pressure Low: 0
Pressure High: 0
Country of Origin: United States

The maxima had a properly working and trouble free air conditioning system until the compressor clutch bearing failed, destroying the clutch. I could not get a replacement clutch. So I got a rebuilt unit. I could not transfer only the clutch as it was a different inside bearing diameter. So I replaced the compressor. The new compressor was shipped dry. No oil drained out of the old compressor. I put two ounces of oil in the new compressor before installing it. The system is supposed to take 6.75 ounces of oil, 25 ounces of R134a.

Do I add any more oil to the system? I suppose I could flush everything and change the dryer, but it is an old car not too much longer for this world, and expense is an issue. There was no other failure of the system. The system was open to the atmosphere less than five minutes. And 134 is cheap. So I hope to merely recharge it and move on.

Thanks for your thoughts.

TRB on Wed July 16, 2008 10:22 AM User is offlineView users profile

Good luck, its always just a guess when doing this type of repair. Might try and drain the oil from the old compressor and see how much you can get out of it. Add that amount back plus an ounce.

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befuddled on Wed July 16, 2008 5:34 PM User is offline

Nothing drained out of the old compressor when I tipped it up. Maybe I should take it apart. Given the choice, I suppose I would rather have too much oil than too little.

iceman2555 on Wed July 16, 2008 6:37 PM User is offlineView users profile

The 'nothing' out of the old compressor is probably the root cause of the clutch bearing problem. The increased resistance of compressor rotation due to the lack of sufficient lubricant resulted in an increase in clutch slippage....thus the excessive heat that destroyed the bearing. The compressor, is more than likely, trashed.....had the new clutch been installed...the same failure would have occurred.....another 'burned' clutch.....another warranty return....yet....the true cause of the failure was not the clutch itself....but the simple fact the system has been operated with an insufficient amount of refrigerant to adequately supply lube to the compressor.
This vehicle uses a Calsonic CWV618, vane type compressor.
If the system is not prepped for the new compressor.....get ready to do it again.
Not only should we 'fix' the problem...but always look for and repair the cause.
But all in all....Good luck with the repair!!!

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

iceman2555 on Wed July 16, 2008 6:38 PM User is offlineView users profile

Opps..forgot...no more than 2 oz added to the suction side of this compressor.....rotate a couple dozen turns....this will lube the vanes and contact surfaces/bearings.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

befuddled on Wed July 16, 2008 11:01 PM User is offline

Interesting observation iceman. So maybe I lucked out in having to change the whole unit. I dumped oil in both ports, and rotated it in both directions a couple of dozen times. A several turns one way, several turns the other way and so on.

The old compressor turned rather easily by hand, no indication of anything dragging inside. I will now definitely take it apart to see what it looks like in there. It never occurred to me that compressor drag could have been the root cause of the failure. Or it could have just been 187,000 miles.

I really appreciate your insight on this issue.

befuddled on Thu July 17, 2008 1:30 AM User is offline

Ok, I have disassembled the compressor. Clever little contraption. It was spotless inside. There were some graphite like stains on the reed valve plate at the tops of the piston's bores. Seemed pretty normal to me, and it was well positioned there by the oil. The pistons, bores, and all of the internal components looked as good as the day they were born.

So about the oil. Considering the stickyness, the fact that every surface was covered, and there was about a half an ounce in some of the nooks and crannies of the case, I have no doubt that there was two ounces in there. And it is pretty clear why nothing drained out. It was either stuck to a surface, or in a cranny that just would not allow it to make its way to the exit.

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