do I vacuum the Auto A/C System?
A: In order to vacuum
the auto A/C system, you need a standard manifold gauge set and vacuum pump.
Start by being sure that all control valves on the gauge set are
closed. With the pressure gauges connected to the A/C system
(red hose to high pressure side and blue hose to the low pressure side) connect
the yellow (center hose) to the vacuum pump. Start the vacuum pump and then
open both high and low side control valves on the manifold gauge set. This
assures that vacuum is being pulled throughout the A/C system.
Typically vacuum is pulled for
about 1/2 hour, but that will depend on the condition of the system
and the work being performed. In the case of regular maintenance, a 1/2 hour
vacuum at 29.9" should be fine. Where a system has been contaminated
or suffered catastrophic failure (ie.: seized compressor) it's generally
a good idea to vacuum for at least 1 hour or more to assure a totally dry
It's also important to assure
that your vacuum pump pulls deep vacuum. Water does not boil until the level
of vacuum is under 1,500 microns. Deep vacuum is considered to be
under 750 microns. Ideally, for automotive service, you should attain
at least 200-300 micron vacuum if not lower. If you're using a typical rotary
vane vacuum pump, you will also want to see this information vacuum pumps
in our 'fast track' section about
using vacuum pumps for auto
A/C service. If you own a rotary vane vacuum pump, you really need to
see this information about
What Vacuum Pump
Manufacturers Really Don't Want You to Know.