Hey guys,

I will try to get to the point and then give the background.

The question: after evacuating a system that has not had any components replaced and had dye, do you need to add any oil or dye when you recharge it?

The tip for other people with AC issues: when my system "worked" it was never very cold (about 60F). I just found last year that the temperature control cable makes a switch behind the glove compartment and was out of adjustment. Since the switch shuts a valve to prevent hot radiator coolant from going through the heater core I was always reheating my ac air. After adjusting how the cable makes the switch the vent air dropped 15F. That adjustment is near the center counsel temperature controls on the cable. I paid 3 mechanics to work on the system over the years and no one ever got really cold air out because they never fixed this issue. One was an AC shop but maybe there are just too many variations out there for them to properly trouble shoot every issue.

The background info: I have owned my vette for 34 years and my brother bought it new 38 years ago. The AC has worked for about 15 of those years. I got it working again last year. I payed an AC shop to convert it to R134a about 20 years ago and it only worked for about 1-2 years. Last year I checked and it had no freon. I evacuated it and found a leak in a schrader when I removed the gauge set. I fixed that and charged the system adding dye. My system originally required 3.75 lbs of R12 or 60 ounces. I understand that you should use about 80% that amount of R134a or 48 ounces. Since I wasn't sure if the system would work or I if I fixed all the leaks I put in 3 cans and some UV dye. The compressor started cycling a little after 1 can. It stayed on continuously when I had 3 cans in. It worked better than ever since I had made the adjustment in the tip above. It put out about 48F air and I think it would do better if I added the 4th can but I wanted to wait and look for leaks. The dye showed I still had 2 slow leaks. One was in the other schrader and the other was the o-ring on the pressure switch on the back of the compressor. No AC shop wanted to just recover the R134a (they wanted to repair and recharge) so I enjoyed it during the summer and hoped the sealer in the can would stop the leak. It didn't and the system is empty again a year later. I bought a compressor O-ring kit from a place in Arizona and will now make the repairs and evacuate it again but I want to know if I should add more dye and oil. I don't think the oil comes out with evacuation and I am thinking the liquid dye may not as well but am not sure. Thanks!

 

based on others asking the same type of question most of the oil should remain but you can add 1 to 2 ounces. Again based on other posts, the dye should be OK.

 

It’s hard to say how much oil is in the system at this point. The oil does not evacuate when vacuuming down.
Too little oil and the compressor can be damaged, too much oil and it reduces the performance of the AC.
For filling I would use a gage set and set it at or near the lowest low pressure reading that keeps the compressor running. Over filing also reduces performance.
If still using a mechanical fan for cooling be sure to jack the rpm to 1200 to 1500 rpm while charging, this insures adequate airflow through the condenser.

 

My .02 if this were my car;

1) AC system is old, 2) started out life with R-12, 3) now has R-134, 4) 3 different mechanics have worked on the AC system.

First I would pull the pump and drain/flush all oil out of it, second I would flush the entire system out than replace the dryer. During this process I would inspect / test all components to ensure they were in good working order.

Once all that was complete I would install the pump, pull a vacuum and add the proper amount and type of oil and charge with R-12.

GM Air Cond systems are not all that complicated but do require proper tools and equipment to service them. I a tool ***** and trust no one but myself when it comes to stuff like this because I will go the extra mile where most AC shops will not.

Hope this helps.

 

Depending on what compressor you have, they will all hold a certain amount of oil (the oil is there to lubricate the compressor to begin with).
When you remove the old compressor, drain what ever oil is in it and measure it.
That should get you close to what would need to be re-added (unless you have a new compressor, which typically already have oil in them).

 

Haynes produced some great automotive AC manuals back in the 80's, look around for one of those. Very detailed and informative for all makes.

 

Thanks. I may add an ounce to be safe as you suggest.

 

Thanks Mr. D. I agree that your suggestions are the best way to get the best performance and know I have the right amount of oil. I don't think I will go this far since it was working and it looks like a pain to get out the dryer. I think I will save that work for when I need a new compressor. I haven't quite gotten to the point or capability of doing all my work myself but am heading that way too. I can just spend more time to do it right (when I figure out what that is!).

 

personally i have done many levels of ac work.
from short cuts to full disassemble.

all i can say is that i have come to the belief that a total
disassembly and solvent flush is the best way to work.

all new seals, shrader valves, and flush of parts to remove all oil.

pull a hard vacuum and weigh and measure oil and freon to add.

good luck

 

I've done like 3 R-12 to R134a conversions and installed my Hot Rod A/C on my vette. If it was mine and I just wanted to get through the next summer, then I would do a good evacuation, get a can of that oil pressurized with R-134a and put that in....that should be sufficient to address any incidental loss. Add R-134a to the estimated requirement (careful not to overfill), and then just get through the season. I am assuming you have the equipment to evacuate and recharge.

ALSO - while you have it emptied out fix these 2 things. It's easy and cheap to buy the schraeder valve and the R-134a compatible o-rings:
"The dye showed I still had 2 slow leaks. One was in the other schrader and the other was the o-ring on the pressure switch on the back of the compressor."