Oil Information For Your Imperial's Air Conditioning System

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Question from Phil: 

I encountered something new while replacing a seized compressor on a lesser Mopar: there was no oil in the compressor.

While that explains the seizure, it raises the question of how much distributed oil there is left in the system.

The manual states that 2 oz of oil for the evaporator and 1 oz of oil for the condenser should be removed from the 7.75 oz of oil in the new compressor.

Since the system probably doesn't have the normal level of distributed oil, I'm inclined to remove only an ounce or two from the new compressor.

Has anyone had experience with this?


From Pete:

This is definitely the great unknown when servicing an A/C system and I've been struggling with it for years.

Theoretically, a properly operating system will circulate oil continuously throughout the system. Some manufacturers have released specs on how much oil pools in each component after shutdown but these are only approximate values.

At the other extreme, manufacturers recommend a full oil charge be added if the system vents catastrophically (as in a front end collision where a hose/line breaks open).

Unfortunately, neither of these conditions apply for about 90% of the A/C systems I've serviced.

If you got no oil out of the old compressor I'd add the full capacity to the system before recharging. I've always erred on the high side when doing this operation and never had a problem. Some of the faulty R-12 A/C systems I serviced over 10 years ago are still going strong.

Do drain all the oil out of the old compressor, though, since the shipping charge can be many times more than a normal full charge.

From Jim:

I was also wondering what I would do about this when I eventually put the A/C back together on my '73.

I'm pretty skeptical about there being much residual oil in the evaporator and condenser in my case, after sitting around in storage in the attic of the garage for 20 years!!

Anyway, I was thinking rather than guessing how much oil may be left in the components, I would just blow out all the component parts with compressed air to remove all doubt about any residual oil, and then add the full amount of oil to the compressor crankcase as they did at the factory.

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