Hello Benzers! I am new to MB's and this forum and have garnered many ideas and information from this board.
In addition to my new-to-me 1989 300E, I also own a 1991 Volvo 740 that I am converting to R134A A/C this upcoming weekend.
I'm lacking a vacuum device that I can suck the system down with and have been considering modifying my 7 horse/30 gal Campbell Hausfeld to provide a vacuum.
My thoughts are to remove the intake filter/baffle and plumb a 5 gallon tank with a vacuum gauge to the intake. I was thinking that if I allowed the pressure side of the compressor to vent that I could get adequate vacuum to do the job. Am I insane? Or is the heat inside my Volvo during Dallas midday getting to my head? I 'd like to hear from anyone who has blown up their compressor attempting this!

Thanks!

Bill Tobin
1989 MB 300E 114K....Mint...I love it....so does my wife, going to steal it someday.
1991 Volvo. 100K. Fast for a big brick fresh out of the kiln.
1992 Maxima....great car, Still a good driver and spare/kid car.....190k

Don't know if that will work, but you can get a air powered vacuum pump pretty cheaply on E-Bay around $30! Just check under HVAC tools!

I've not personally tried it, but have read stories of the results of others. The end result was that a compressor cannot pull a deep enough vacuum to boil out all the moisture. My fuzzy memory says about 16" of vacuum is about all you can expect. Even at current Dallas temperatures you need to reach 28" or more to remove all the water. So no, it ain't gonna do the job right.

What part of town are you in? I've rented vacuum pumps before, specifically at Taylor Rental on North Central Xpwy in Plano.

I live on Custer at Mcdermott at the Frisco/Allen/Plano line. I think I'll take your advice and rent one. I would hate to tear out the A/C comp, replace all the O-rings and drier, put all the stuff back on and charge it just to have it cool poorly because of moisture.
Just one question tho. The compressor and tank are capabile of 150 lbs. Is the intake vacuum not capabile of approx. the same....? taking into consideration the 5 gallon tank opposed to the 30 Gallon on the pressure side.

Thanks!

Bill.

All I can say is that I've read it won't pull anywhere near a perfect vacuum. Just because it can produce high pressure on the output side doesn't mean it can produce high vacuum on the input side, I guess... Dunno, I'm not a mechanical or fluid engineer.

The a/c will work just fine if you pump it down to 16" - you won't be able to tell the difference. The problem is residual moisture in the system reacts to form hydrochloric acid. It'll work fine for a year or two, or perhaps more. Then one day there will be no refrigerant in the system, and *everything* will need replacing. It's called an acid eat out. That's why a deep vacuum is so important.

Here's what I've seen! Seems like a safe and cheap way to go if it works as described! I haven't any experience so if anyone does I'd be happy to hear it as I anticipate some AC work in the near future!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1826859697