How much oil to add to a/c - Page 2 - PeachParts Mercedes-Benz Forum

ROLLGUY · #16 07-12-2015, 12:29 AM

Quote:

Originally Posted by nelbur

I have been frustrated at the inability to determine if there is oil in an old system. I have converted two old cars from R-12 to 134a, and in both cases I was not able top find any oil in the driers or compressors. Both were still working so there must have been a bit of oil but most had apparently leaked out with the various freon leaks over the years. I have since discovered that I can get a feel for the existence of oil in a system if I open the low pressure valve briefly while the system is running. Since the valve works just like a tire valve, pressing down on the stem opens the valve. The refrigerant and any oil circulating with it will squirt out on your fingers. Once the refrigerant evaporates there should be some oil on your fingers. It is my assumption that having a noticeable amount of oil is all that is needed. I am not an expert, and I am sure an expert will find this subjective oil measurement ridiculous. However, I now have an idea as to how to decide when to add one of those oil charge cans.

Most if not all compressors nowadays have a sump (unlike the GM R4 in most of our cars), so not much oil is needed to circulate with the refrigerant. Although not "ridiculous" IMO, opening the valve briefly is a good way to tell if there is any oil circulating, but NOT a definitive way to know the quantity thereof.....Rich

vtmbz · #17 07-13-2015, 03:37 PM

To finish this up: the enviro safe website shows a chart of pressures to temperatures as a guide to refilling. I was using that as a guide. The can of freon actually says to keep the low pressure between 32 and 42 psi. I checked today, and I am at 45 psi.

In rechecking I did as suggested and let the low pressure leak onto my fingers; it seems my fluid is quite oily. So, while not scientific or even slightly methodical, I decided not to add any more oil on the basis of that test. Thanks to all who contributed! My cooling system/ac renovation is complete and everything is working like it is expected to work.

Next up: how come I don't have kickdown, anyway?