The following guidelines are for
domestic through commercial
applications.
System size (tons) Pump cfm
1-10 1.5
10-15 2.0
15-30 4.0
30-45 6.0
45-60 8.0
60 and above 11.0
2. How much of a vacuum should I pull?
A properly evacuated system is
at 2500 microns or less. This is
1/10 of one inch and impossible to
detect without an electronic vacuum
gauge. For most
refrigeration systems, ASHRAE
recommends pulling vacuum to
1000 microns or less. Most system
manufacturers recommend pulling
to an even lower number of microns
between 300 and 500.
3. Do I connect an electronic vacuum
gauge to the system or pump?
To monitor evacuation progress,
connect it to the system with a
vacuum/charge valve.
4. Why does the gauge micron reading
rise after the system is isolated from
the vacuum pump?
This indicates that water molecules
are still detaching from the system
interior surfaces. The rate of rise
indicates the level of system
contamination and if evacuation
should continue.
5. How can I speed evacuation?
A. Use clean vacuum pump oil.
 Milky oil is water saturated
and limits pump efficiency.
B. Remove valve cores from both
high and low fittings with a vacuum/
charge valve tool to
reduce time through this orifice by
at least 20%.
C. Evacuate both high and low sides
at the same time. Use short, 3/8"
diameter and larger hoses.
D. Use a heat gun.