Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

Vacuum Q

D.T. on Fri July 11, 2008 6:23 PM User is offline

Refrigerant Type: 134a

I am going to replace my compressor next week and I have been pulling a vacuum on the system with my Mastercool 3 cfm single stage pump. Thing is my gauges say 30" of vacuum but the gauge from my hand held vacuum pump (manual) I only get around 28" of mercury at best. Since I assume this is not a deep vacuum and the pump is rated @ 75 microns (this is near 29.95" of mercury) that my pump isn't performing very well.

I am going to try the triple evacuation method since I can't seem to get a deep vacuum. Also, is there a conversion chart out there that compares all of the different vacuum measuring units? Like Pascals, Torr, Microns, Inches of water, inches of mercury, etc. etc....

Any thoughts?

Too many questions, not enough answers....

retrofit on Fri July 11, 2008 7:42 PM User is offline

Here's a x-reference table

mk378 on Sat July 12, 2008 12:48 AM User is offline

You have two gagues that read differently when connected to the same pressure. One of them must be wrong.

At elevations higher than sea level, a full vacuum is less than 29.95 on a dial gauge. The gauge reads the difference between atmospheric pressure (which varies with altitude and the weather) and system pressure.

bigkev on Sat July 12, 2008 3:30 AM User is offline

make sure your gauge is zero at rest. There is a little adjustment screw usually covered by a plug on the glass/plastic on the front of the gauge.

Chick on Sat July 12, 2008 6:01 AM User is offlineView users profile

While a good gauge set is accurate, you are taking about between 1 and 1/10hg on your gauge, so for this purpose, it's accurate, but "not" as accurate as a micron gage.. As mk378 stated, you will lose 1hg for every 1,000 ft above sea level.. But if you're pulling 30hg on the gauge, either it's not zeroed in, or it's just that it's off that 1/10 to 1hg.. Don't obsess over it though....

Email: Chick


Freedoms just another word for nothing left to lose

D.T. on Sat July 12, 2008 8:24 AM User is offline

Originally posted by: retrofit
Here's a x-reference table

That's the sh*t there, just what I was looking for.

Vacuum Defintion

I could obsess over it, depends on how well I want my system to function. Seems like time and money are factors.

We are only dealing with medium vacuum levels here also.

Too many questions, not enough answers....

Edited: Sat July 12, 2008 at 8:28 AM by D.T.

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.