I just spent two days completely flushing out the dual A/C system on my 96' Dodge Grand Caravan (yes I know that's not a Mercedes, but I want knowledgeable responses, so I'm cashing in my chits for all the Mercedes related contributions I've made in the past).
I wanted to restore the A/C system to factor condition, purging the leak stop I'd put in the system before I knew any better. I also wanted to know exactly how much oil and refrigerant was in the system - down to the ounce.
I replaced the compressor, both expansion valves, and all o-rings. Removed and flushed everything else, which is a real pita on the rear system.
I pulled a vacuum to 29 inches for two hours with the 17.7 cfm pump. It held for 24 hours without any movement - none!
This morning I began filling the exact amount of R-134a (3 lbs). I decided to use 12 oz cans so I could get the exact amount. At about the end of the third can the high pressure gauge was reading 250. I know because I was looking at it.
That is when it happened!
The POS Interdynamics Gauge Set blew at the high pressure hose just above the coupling and the line valve. (See Attached Picture - also note the 600 PSI working pressure!). It spewed refrigerant and oil for about 15-20 seconds before I threw a towel over the hose and pulled the quick disconnect. I have no idea how much refrigerant I lost or how much oil I lost.
I know I lost both - the oil was evident all over the engine compartment.
I figure the only way to know with absolute certainty how much is in the system at this point is to break it all down, flush it again, and start from scatch.
After some kicking things around the garage I decided to go ahead and add the last 12 oz can. The system puts out some nice cold air which is great after years of crappy service thanks to my mucking up the system with leak stop (before I learned about the right way to do things).
Finally, here is my question: how do you think I should proceed.
1) Add in a 2 oz oil / 2 oz refrigerant charge just to be safe (but run the risk of adding at the most an extra oz of oil).
2) Let it go with slightly less oil and refrigerant than is required by factor specs.
3) Tear the whole thing down and make damn sure I've got the exact amount of oil required - keep in mind I just bought a new (not remanufactured) compressor.