PeachParts Mercedes-Benz Forum - Need R134 A/C conversion specs for W201

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But a question: do I pull and hold the vacuum before or after I add the oil?

After I would imagine. I dont think much of the oil comes out when you vac down. Could be wrong though..

The last 4 cars I've done I've vac'd down for an hour, let it sit for an hour, then charged up if everything held.

The one truck we did where we put an entire system in, we added oil then vac'd down for an hour, found a leak, fixed it, re-vac'd and then waited another hour. After that we charged it up with the appropriate quantity. Works pretty well.

I pulled a vacuum on it and shut the valves and pump off a couple of days ago, mostly to check for leaks, and it held. Would that count as running the vacuum pump for an hour?

How long was the vacuum pump running?

Long enough to pull a vacuum, about a minute.

If it were me I would not consider 1 minute adequate.

Ideally till it the vacuum is around 500 microns but I don't have that kind of equipment to read that, like the quote says below:

Quote:

Question – How long does the vacuum pump need to run for?

Answer – This is a question that even AC certified technicians such as myself disagree on. The minimum is 15 minutes, the longer the better. A recent article I read in an AC trade magazine discusses “how much vacuum is enough?” in great lengths. They say to keep the vacuum pump on long enough to achieve vacuum measured below 1,000 microns (preferably down to 500. This is nice to know in theory, however most technicians have analog AC gauges which measure vacuum in inches of Mercury (inHg).

Denlors Auto Blog » Blog Archive Car AC Vacuum Pumps – FAQ’s | Denlors Auto Blog

But its not like you removed the vacuum from the system and charged into it directly... But if you closed off the valves and let it sit under vacuum for a while.. where does all the "boiled off" moisture go? It has to go somewhere.. If the vacuum pump was running it would have got sucked out and exhausted out the vacuum pump.

Any moisture would be as a vapor in a vacuum, even though it wouldn't go anywhere. Then in theory I could turn the vacuum pump back on and it would suck out the water vapor. I was thinking it takes time for the water to boil off to a vapor and as long as the vacuum stays low enough it should all be a vapor.

That was my theory, not that I checked it, I still ran the vacuum pump for a while. My real intent was to check for leaks and I don't have anything good to pressurize it with.

Pressure Testing AC

Are you guys doing any kind of pressure testing before Re-filling ?

Y'all know you can have a Leak(s) that cannot show up under Vacuum,
BUT is excruciatingly obvious when the system is pressurized with say Nitrogen.

When switching Refrigerants (Unless some genius had previously installed
lubricant that is safe to use with both "Before" and "After") The Compressor
is NEVER Flushed,BUT must be turned BY HAND until ALL the Old Lubricant is
removed.

No, I've never done any pressure testing. Never had access to nitrogen. It was always something that was going to be done "when I got around to it" these vac down and recharges were one of those "fix it temporarily and we'll deal with it how we originally wanted to later on"

Later still has not arrived. But yes the proper way is to check for leaks with pressure, like from dry nitrogen.

So far anyway, I'll have to wait and see how long it lasts.

98 deg. outside, 46 deg. in the vent, nominal pressures. I'll do another pressure check is a little while.