Advice needed: A/C - You can do everything right, but then there is the weakest link! - PeachParts Mercedes-Benz Forum

pwogaman · #1 07-23-2006, 12:38 PM

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.

jwhughes3 · #2 07-23-2006, 12:56 PM

I start with a disclaimer that I am no expert....

After reading of your misfortune, I can read in your post that you need someone to tell you to re-flush and measure it all back in correctly. At least that is my take on it and that is my advice - you spent all the time and effort to get it back factory right, go ahead and re-do the easy part. You'll sleep better and you know your compressor will last longer.

John

pwogaman · #3 07-23-2006, 01:00 PM

Thanks for your response. One important piece of information I neglected to add. The factory oil charge is 13 ounces. There is no way not even near that much got out.

Please don't construe my message as looking for an excuse to do it all over again. I will just as gladly take accept that it is okay to do 1) or 2).

Let this also be a lesson the everyone to wear eye protection. I was and it was covered with trace amounts of oil.

Brian Carlton · #4 07-23-2006, 01:21 PM

Quote:

Originally Posted by pwogaman

Thanks for your response. One important piece of information I neglected to add. The factory oil charge is 13 ounces. There is no way not even near that much got out.

Instead of just winging it, or providing a "feel good" response, let's look at the facts.

The system needs 13 ounces of oil.

You lost a certain amount of oil. We don't know the exact amount, but, are fairly sure that it's between 1 and 3 ounces of oil (judging strictly by your comments). So, if we add back 2 ounces of oil, we can have a situation where we are one ounce light on oil.......perfect.......or one ounce heavy on oil.........or anything in between.

In percentage terms, as compared to the original 13 ounce fill, the error is a bit under 8%..........worst case condition.

You'd have a very hard time convincing me that the factory must have an oil fill to 13 oz. and an error of 8% one way or the other would create any issues in the system.

My advice is to add 2 oz. of oil and be done with it. The chances of a problem to the innaccuracy of the amount of oil in the system are virtually nil.

JimmyL · #5 07-23-2006, 07:02 PM

I'm in complete agreement with Brian on this one. Easy for us to tell you to flush it all again to do it right, it's another thing to redo all those orings, dig to the rear evap, redo both expansion valve orings/connections, etc.....(no offense to your post Hitman. Remember, this is a dodge.....

)
Errr on the side of slightly too much oil. Slight cooling compromise is better than being a tad low in my opinion.
That was quite a job to tackle. Uhhh, and get a better set of gauges Mister......

jbaj007 · #6 07-23-2006, 07:27 PM

Take a bottle of "Simple Green" and weigh it on a postage scale. Then spray the areas of oil mist, trying to cover the same surface area and density of the misted area. Don't forget to do the towel, also. Weigh the bottle. Take ~difference (oil is lighter than water, I know) and you've got a great approximation of how much oil was lost...........AND you've cleaned up the mess

. I think it will be less than you imagine.

Reclaim the R134a, add the amount of oil needed, vacuum and charge. At least it worked on paper

.

Motorhead · #7 07-23-2006, 01:07 PM

Man I feel for you.... Here you try to do everything right and old MURPHY rears his ugly head.
I would try to take your BEST educated guess and add the amount of oil you think you lost. I think you wouldn't go wrong to add 2oz.of oil. Too much oil and the efficency goes down, too little and you risk the compressor. I would also recharge the system to specs as far as the amount of R134. Running the system low on refrigerant works the compressor harder. Buy a new set of hoses for your A/C gauge manafold.
I NEVER mind trying to help guys when they ask for help on their other wheels. Good luck. Chris

Hit Man X · #8 07-23-2006, 01:08 PM

You've come this far, finish it properly.