View Single Post
billybek billybek is offline
Registered User
billybek's Avatar
Join Date: Dec 2007
Location: Calgary
Posts: 6,411
Originally Posted by 88911coupe View Post
Just to clarify the test I just did was not hooked up to the ac system, it was just the hose hooked up to the pump and micron gauge. Basically just wanted to see what the vacuum pump can do.
A good pump should be able to pull down to about 40 microns (29.915"). Was the charging manifold (gauges) attached to the vacuum micron gauge?

Could be improper oil level in the pump. Too high or low some pumps are fussy about that.

When was the last time you changed the oil on the pump?
Change the oil after each use.

The "ideal" vacuum of 500 microns on the system is a good indicator that the system does not have any leaks. On a 911 ac system with what seems like miles of hose will be difficult to get that low. Refrigeration oil in the system and the hoses out gassing plus residual refrigerant you would probably be lucky to hit 700-800 microns on a new clean system. YMMV

Interesting tidbit of info (maybe!) that at 500 microns, the pressure in inches of mercury is 29.90. Pretty close to a pure vacuum!

Your measurement of 1850 Microns at the pump would be about 29.85" hg gauge.
29.90 and 29.85" would be pretty difficult to see with the compound low side gauge.

I am not a huge fan of leak testing a system using a vacuum. Leaks allow air and moisture into the system and some types of refrigeration oil is highly hygroscopic and will absorb the moisture from the air.

Try to isolate your equipment problem to pump, hoses or manifold and see if you can get that pump to perform.
Bill K.
"I started out with nothin and I still got most of it left...."
83 911 SC Guards Red (now gone)
And I sold a bunch of parts I hadn't installed yet.
Old 07-23-2017, 02:38 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #35 (permalink)