I charged my car AC with R134a refrigerant about 2 years ago as it was not cold enough during the high temperature of summer days, it kept working well until this summer where it is showed similar signs, so I went to the mechanic to check & we found the coolant mass to be 0.36 kg and oil was 7 ml after vacuuming the AC into his automatic refilling machine (if that name is correct)

He then recharged the AC till 0.5 kg refrigerant & 50 ml oil & then the AC became good again.

My question, how did the coolant decrease within 2 years while (supposedly) there is no leak (if there was it should deplete faster maybe & it wouldn't be possible to have that vacuum, right??)

  • Keep in mind that the recovery machine only pulls out any oil in solution with the refrigerant. It leaves a lot more oil inside the system (the only way of restoring the proper oil level is flushing the entire system, balancing the new oil charge across the system components, turning the clutch hub by hand a certain number of times after installing the compressor and charging the refrigerant, so that it won't try to pump any liquid oil, and letting the engine idle with AC on for at least 5 minutes during the first startup). Too much oil can seriously hamper cooling and damage the compressor.
    – Al_
    Jun 2, 2018 at 17:29
  • Modern cars work with a low refrigerant charge. Not letting the compressor run for a few minutes each month, or even better week, can make the o-rings and compressor shaft seal dry up of any oil and accelerate natural gas leaks (inherent due to the presence of seals) and a little reduction in refrigerant level can, in addition to wear the compressor faster due to lowering the oil circulation rate inside the system, hamper cooling performance especially in very hot weather.
    – Al_
    Jun 2, 2018 at 17:34

1 Answer 1


There are levels to vacuum.

Practically speaking, car A/C systems cannot be 100% leak-proof, which is why service manuals consider a system air-tight enough if it can hold vacuum at a certain pressure level.

What the mechanic should have done was ensure that the system was able to hold sufficient vacuum for a sustained period of time before recharging the system. If it doesn't meet the vacuum specification, the system is leaky enough to lose refrigerant over a couple of years.

Possible sources for leaks include:

  • hairline cracks in system components
  • punctures in the condenser
  • cracked fittings
  • worn/ageing seals
  • Thanks for your answer, the system could hold vacuum for around 10 minutes or more I think, after that he started the refilling. I wonder if I should troubleshoot the system & look for leaking or keep it as is since it could work well for the last 2 years Jun 2, 2018 at 16:57
  • 1
    You can diagnose the condenser by yourself in the meanwhile. Just get a good view of it. Any oily patch means leak. If you can get a blacklight torch and shine blacklight over the condenser, inside the gap between it and the radiator and along any component you can reach (piping, AC compressor body, TXV valve, receiver etc) it's even better because lubricant oil often includes a green UV dye to simplify leak tests (and if there's no dye, you can ask the AC guy to inject it, although the machine usually shows the reclaimed oil in a separate bottle, and dye-laced oil has a light green tint).
    – Al_
    Jun 2, 2018 at 17:47
  • 1
    You're welcome. I still have ice cold AC in my 15 year old car. So cold that i have to turn the fan down and point the vents away from me to not feel sick, especially after thoroughly washing the condenser's fins and restoring the sealing foam between the condenser and the radiator. All that was replaced in these years is the compressor's clutch coil and the receiver-dryer. Take care of your car's AC, and it will take care of you.
    – Al_
    Jun 2, 2018 at 20:28
  • Touch wood ! :) , the problem is that in Gulf it is so hot & ACs work so hard & I think this shorten their life & their performance in time (temperature here reaches 56 degree celsius in summer) Jun 3, 2018 at 17:44

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