Curious, how would you know if your compressor has oil? When I got into an accident the condenser had to be replaced, but I left it empty of freon because it was cold back then. I had it recharged with freon (ok, R12) but I now think I didn't have the oil checked, so how do I know?

I rarely use my AC but I'd like to know I'm not killing the compressor by running it without oil...

Edit: car is 1983 300D

Also, receiver/dryer glass isn't as clear as it's supposed to be. Your thoughts?

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Putting the right amount of oil back into a refrigeration system after it has been leaking is a black art unless you completely flush the entire system and put the correct amount into an empty system.

To make it worse, the location of the leak will have a lot to do with how much oil gets out with the leak.

Did you replace the condensor? Did you have it repaired? If either of these questions get an affirmative answer, you probably need to add about two ounces of mineral oil.

Good luck,

Thanks for the reply Larry.

The condenser was replaced with a new one, but the rest of the system wasn't. What would it take to "flush" the entire system? The reason I ask is because I don't have very cold AC, and when I turn it on again after a while, it gets less colder, and then barely.

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If you have a GM A6 compressor which was common on a lot of MB's at the time, There should be a cap on the bottom of the compressor reservoir. Run the AC turn it off and crack the cap. If vapor only comes out you need more oil. If a bubbly foam of oil comes out your good. That was the proceedure for GM vehicals that used this compressor at the time. MB may have a different proceedure.

John Roncallo

I had to replace the compressor in my '91 190E. It failed due to lack of oil. Sounded like a garbage disposal when it let loose. When I found out it was dry, I asked my mechanic to check my other car, a '87 300E. Sure enough, it was very low on oil. He put in the reuqired amount and it cost $70. A far cry from $1200. This is the original 18 year old compressor and it runs full blast for about 6 months a year as we live in the low California desert where temps easily hit 115F.
Anziani

I had an auto-tech instructor about twenty five years ago who gave me some great advice. He told me to evacuate and re-charge the A/C system every three years and add about four ounces of refrigeration oil. I've done this to every car I've ever owned and have NEVER had a failure of any part. This may be especially good advice to owners of MB's with suspect evaporators. Here's why. With age, the oil can accumulate moisture. If I remember correctly, the moisture mixed with the refrigerant has a certain amount of acidity to it. When the A/C is not in use, a lot of oil sits in the bottom of the evaporator. This is what causes them to leak. The damage is from the inside out. Those of us who have replaced evaporators almost always find the leak in the same place. On the BOTTOM.

The late 123 300D's had GM R4 compressors.

Evacuating the refrigeration system every three years and adding 4 ounces of oil every time will ultimately lead to a severe oil excess. Severe oil excess will lead to a severely locked up compressor.

Flushing the entire system is not too big of a deal as long as you are equipped for it. It means you will need a good vacuum pump (preferably in a recovery/recycle machine,) manifold gauges, a flush gun and cannister, flush agent and a good air compressor.

If you have the proper equipment, simply recover any refrigerant and break all connections and use your flush gun and cannister to push flushing solvent through each component individually and then MAKE SURE that ALL flushing agent is blown out of every component. With the ENTIRE system flushed with solvent EXCEPT the compressor which is flushed with refrigerant oil, put the correct amount of oil in the system which I think is 8 ounces. Pour an ounce or two in the compressor if it will fit and then of the remaining 8 ounces put half in the evaporator and half in the condensor.

Connect everything back up with new o-rings, putting a new receiver/dryer in place LAST. Evacuate and charge the system.

Good luck,

In theory this statement makes sense, but several factors must be considered.

1. If the system evacuation is done CORRECTLY, several ounces of oil will be removed along with the refrigerant. (With the vehicle at operating temperature and the A/C on, the evacuation should begin immediately after the engine is switched off)

2. Has the system had any leaks repaired in the past? MB work instructions recommend a certain amount of oil be added depending on what part was replaced, but if the system has lost ALL refrigerant it most certainly has lost some additional oil as well. In fact, the oil is what makes it possible to visually diagnose A/C leaks in the first place.

3. I'm glad you mentioned the GM R4 compressor. This unit was not exactly known for it's durability. My 91' Buick has one. After fifteen years it's still using R-12 and it's as quiet and efficient as when it was new. If it weren't for periodic TLC it wouldn't have lasted this long.

Your instructions on how to properly FLUSH an A/C system are right on the money, but from a maintenance standpoint I think it's overkill. A total system flush should only be necessary if there's been a catastrophic compressor failure. On the other hand, if a DIY'er has access to the proper equipment and doesn't mind spending the time, why not? I certainly wouldn't recommend paying to have this done as a preventive measure though.

I agree with Larry, my recycler catches the oil as it discharges the system and I have never had more than an ounce come out. It depends to a certain degree how fast you discharge and where the service ports are located.

As most systems only use 8oz or less, putting 4ozs in every few years quickly exceeds the full amount. I was always taught that too little oil was better than too much.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician