this is not another "passenger vents blowing warm" or "how to recharge the ac" questions.

I've been having problems with my AC holding a charge for a few years now. I use a manifold gauge set to recharge/check the system a few times a year. I put dye in the system and could not find an obvious leak although i suspect the evaporator may have a leak where i can't see. Also noticed sometimes the engine fan won't kick on when the a/c is turned on and i have seen the high side pressure spike way up. I believe that the relief valve on the compressor may bleed off refrigerant during these pressure spike also contributing to the problem.

My main concern is that i now have no idea how much oil i have in the system since its leaked out and been recharged so many times. I always use pure R134a to charge the system and have added a small amount of oil to account for any that leaked out. Now the compressor is starting to make noise when the clutch is engaged and runs very hot. So i would like to start all over so to speak and evacuate, disassemble and clean, fix any leaks, and recharge the system with the correct amount of oil before the compressor blows up.

First i was thinking of pulling a deep vacuum on the system to see if there is a leak in the evaporator or elswhere. I really don't want to pull the dash out because at this point it seems like i may as well replace the heater core and all the HVAC doors while i'm in there and i really don't want to do this (since there not broken yet). If it holds a vacuum i was thinking of flushing out the system (with the correct flush fluid of coarse), replacing the orrifice tube/line and dryer, o-rings on lines, and then recharging the system and adding new oil (its 4oz i think). Would this work? Can you drain the oil out of the compressor and if the rest of the system is flushed then is it safe to assume there is no oil in the system and add the full amount?

And does the a/c system run when you have the heat on? For this winter if i pull the a/c system could i run a shorter serp belt for a non a/c truck and have the heater work ok and not risk being stranded if the compressor locks up?

Thanks for any advice!!

 

You'll never get the oil out by vacuuming it. You might not get any. The only sure way is to remove the parts and pour it out. The dryer will have to be replaced, especially if you have to open it up for more than just a brief moment. You might as well bite the bullet and change the evap and heater cores. When I dug the one out of the 99, I was shocked as to how much gunk was caked on it by just a small film of oil leaking. I'm not even sure how air was passing thru it. there was no other oil in the case. Just the film on the face of the core itself, with dirt stuck all over it. And when you have a leak, very little oil is being lost, unless it's a gusher. A small leak will let out only enough oil to collect a film of dirt. They'll be more than that left behind in the container you initially measure with to fill it.

If it were me, especially with the heat breaking, I would take that belt off that compressor before it grenades and fill the system full of debris. Yes, you can run a non ac belt. Just find a pic of the diagram and follow it and put it on. The drawback is not having the ac on in defroster mode. Part of that process is drying the air with the ac before it's blown over the glass.

Also get three ball valves and setup an H bypass system with the heater hoses. That's what GM tried to do years ago but the valves would rust away and everyone got rid of them. Think about it. Your taking air, passing it over the heater first, which is right a 190, then your asking the ac to cool that to about 45 or 50. That's alot to ask these ac systems to do, but it's what's going on. Stopping that 190 plus water from going in there will feel like a massive ac upgrade. The valves will allow you to turn the heat back on quickly and also circulate fresh coolant into the heater to keep it from corroding away.

 

I was at a Napa auto parts dealer a while ago. There was a salesman there with an chemical injection kit for your a/c system that causes freon to coagulate if it contacts air. It was only out for the last year and not many a/c shops carry it. He said it will seal very small leaks which are hard to detect. Maybe this will help. Also check all connections for signs of oil on them. And most a/c connections use o-rings so don't over tighten or it could distort them causing a leak. A good a/c shop will have an electronic sniffer device that may detect the leak. The compressor seal is a possible culprit.
A small leak won't really shed any oil, but if you were to cut a line or quickly open a fitting, a mass evacuation would take place and carry out a lot of the oil. This is similar to opening the water drain valve on a compressor. I agree that if there is a bad noise when the a/c is activated, don't run it. An a/c system contaminated with compressor debris will give you years of headache even after being repaired. There is a tiny orifice which through freon passes. One piece of debris in it greatly reduces efficiency, and plugged stops the a/c completely and will require mechanical disassembly each time.

 

How high is the high side pressure getting??? Enough to kick out the compressor?? Good chance your orifice is plugged, While running the a/c are your low side and high side pressures the same? I would do some more troubleshooting. What are small amounts of oil-- 2 oz of oil per comp. I think and everyone might prove me wrong is that you need to pull the vacuum for at least 30 mins, stop the vacuum and monitor for at least 15 mins. Also make sure your sherder valves are not leaking. Use soap and water. Sorry If this is elementary to you.