How do I know how much R12 to add and wether I need to add oil? Anyone? Anyone?
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So many donuts, so little time.

Are you in the driveway? Shop?

In my driveway - adding R12. First check sight glass, note bubbles. A very few and sort of oily slick oozing in there - very empty. Very few and no oily look - full enough to leave as is. Soadsuds look? Add a can (12 ounces to a can.) Check label on inner LF fender, I think it says full = 48 ounces.

Hook up to add one can. Keep can upright. Watch sight glass and frost level on can. If can goes in and you still have soapsuds bubble, hook up another can. Expect that one to be the last one. Overfilling can give problems of greater $$$ repair than does underfilling.

Note that this is highly non-technical, but it works for me. I have studied a/c and have a pretty good idea of what's what. Take things slowly, and be aware that the 300+ psi pressures that an a/c system can develop can do serious harm to human flesh and eyes.

Good Luck,

Bob

:>)

If you have a gauge set go to http://www.aircondition.com/ and download the AC advisor program ( in the left hand column ) it has a handy calculator for figuring pressure to outside temp.
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '82 Mercedes 300SD for sale

Great link for those of us who are EPA certified for auto AC yet only know enough to be dangerous. (aren't internet liscensing sites great?)
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Dave Shannon
Spring Valley, California
'67 1800s
'73 1800ES
'88-240
my pages

That test thing is a riot. lots of regs and theory but no useful information.
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '82 Mercedes 300SD for sale

Yea, it's strictly a "pay your $15 and get legal" thing. Fairly useless, that's why I like that converter so much, that temp/pressure thing is priceless!
Cheers
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Dave Shannon
Spring Valley, California
'67 1800s
'73 1800ES
'88-240
my pages

http://www.imaca.org/

Download the booklet, look through it so you know what the sections are and take the test with the book next to you. With the cert' if anyone tries to turn you in for working on your AC you're covered. I've bought several different batches of refrigerant and been asked about 1/2 of the time for my cert' the rest of the time it was $$ only. I haven't bought R-12 with it however, I figure I'll need it for that if I ever run out.
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Dave Shannon
Spring Valley, California
'67 1800s
'73 1800ES
'88-240
my pages

Well unless you do a complete evacuate and recharge which is 2.9 pounds on a 240 you are just making an educated guess at how much to add. Seeing as the system holds damn near 3 lbs you would probably be safe adding 8 ounces or 1/2 a pound and checking. You need to have guages so you can monitor the pressures both high and low, monitor the outlet duct temperatures both before you've added gas and after, and pay attention to how much the compressor cycles. What method do you have of weighing the amount of refrigerant and what kind of guages do you have to dispense the stuff and monitor pressures? Are you just using cans? If so then suck in half a can and see if it likes it. Most R-12 you find these days is in a 30Lb jug but the ocassional can will surface here and there. A three ounce oil charge would not hurt things and in all actuality will probably help.

Mark

I am preparing to charge my AC in my '89 with refrigerant. It is still using R-12.
What kind of pressure readings should I be seeing before and after adding refrigerant?
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'80 DL 2 door, '89 DL Wagon