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My 1999 Suburban's A/C started to lose its cooling capacity last fall. In late fall it stopped cooling completely (there was a mechanic involved with other parts of the vehicle at the time). This spring it still does not cool, although antifreeze levels are good.

I'm planning on checking refrigerant pressures -- there might be a slow leak and the levels might be low.

If the pressures are low, we're going to start with a full recharge. I plan to evacuate the system completely and properly dispose of the old refrigerant, then recharge the system. I will also add some fluorescent dye.

Currently all the A/C parts are still OEM original. Since there was no parts replacement, would that eliminate the need to add oil? Or should I still include oil during the recharge of the A/C?

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To answer your question you put back in the same amount that came out when you evacuated the system. If none came out I usually add 1 to 2 oz depending on the size of the system.

To address another part of your question why would you dispose of the old refrigerant? Most recovery machines also recycle the old refrigerant, by that I mean that they remove any moisture, air and contaminates. Deposing of if cost you money, plus the cost of refrigerant.

Pressures alone will not tell you if the system is charged correctly, while it can give you an idea you won't know for sure without measuring it, especially if non-condensable gas (air) is in the system.

If you have a recovery machine it will tell you the amount of refrigerant removed and you can compare that with what is suppose to be in it.

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Thanks, this is helpful. –  musicwithoutpaper Jun 28 at 16:37

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