Auto AC rules of thumb

[andrew vanis]

What rules of thumb exist in Auto AC?

Below are the ones that come to mind for me. What others exist? Please correct the ones posted as appropriate. I can update this first post with corrections and additions as they come up in additional posts. Maybe it can become a sticky/FAQ. Thanks in advance for your knowledge and contributions.

Rules of Thumb

System pressure in PSI equals ambient temperature in F when the system is not being used and has not been used for a while.
Such result typically means system dues not have moisture/air or other contaminant in system. (Is this true just for R134a or also other refrigerants?)

High side pressure when running showing 3x ambient temperature typically indicates a good functioning system.(Is this true just for R134a or also other refrigerants?)

Don't use sealers, "fix in a can" etc. They make a bigger mess to clean up, can mask real symptoms causing a more difficult fix. Use only specified refrigerant, oil, and as appropriate dye.

Vacuum - Standard gauges do not have enough resolution for vacuuming/leak detecting a system. Ideally use a micron gauge to get to and keep 500microns

Pressure testing - don't use compressed air. It can affect the desiccant in the receiver/drier introducing moisture into system. Nitrogen is preferred and then needs to be vacuum evacuated.

What minimum times/pressures do the pros recommend for the following

1) vacuum of ? Microns holding for ? Minutes/hours is considered a leak free system

2) pressure test of ? PSI holding for ? Minutes/hours is considered a leak free system. (Nitrogen is the preferred gas. Don't use compressed air.)

[andrew vanis]

Remember to service your tools...from the FAQ section

This is a great post by swampy

viewtopic.php?t=14940

[andrew vanis]

Discussion on evacuation times in the FAQ section

viewtopic.php?t=14619