Re: 308 A/C work
From: Todd Walke (racertodracertodd.com)
Date: Sat, 15 Mar 2008 20:24:26 -0700 (PDT)
Rick wrote:

About 15 minutes later, I took an hour-long drive with
cool air circulating around my person. :-)

Hope you enjoyed the story.

Sweet! My first time recharging a system was a bit daunting. Mastercool makes a nice instruction book with all sorts of theory on how auto A/C systems work, practical procedures and troubleshooting information.


One note on the air-operated vacuum pumps. They pull about 28.3 inches of vacuum. Standard air pressure is 29.92 inches of mercury so 28.3" of vacuum is the same as 1.62" of mercury (29.92-28.3=1.62).
At 28.3" of vacuum, water boils at about 95deg F or so. That's barely enough to boil the moisture out of a system in hot climates, but not in more moderate areas. The vacuum pump needs to lower the boiling point inside the system to below ambient. The lower the boiling point, the faster you can get all the moisture out.
A proper A/C vacuum pump will pull down below 100 microns of mercury. That lowers the boiling point to well below zero which gets the moisture out very fast even in cooler climates.
I attached a chart that shows the boiling point of water at various pressures.


I also used a fluorescent dye in the oil to help in tracking down any leaks.


Todd Seattle,WA '86 GTI, Red of course. (exciting racey car) 268,000 miles '87 Golf, Polar Silver. (boring work car) 649,000 miles <- Yeah, baby! http://www.pureluckdesign.com <-Ferrari & VW stuff

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  • 308 A/C work Rick Lindsay, March 15 2008
    • Re: 308 A/C work Todd Walke, March 15 2008

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