Evacuating The System; Evacuation Hookup; System Vacuum - Piper Dakota Maintenance Manual

EVACUATING THE SYSTEM

If system has been operated in a discharged condition or anytime system has been open to atmospheric
pressure, replace receiver-dehydrator and evacuate system to remove any trapped air and moisture which has
entered it. Use a vacuum pump capable of pulling 29 inches of mercury or better. As air conditioning system
pressure decreases the boiling temperature of water (moisture) that may be present also decreases. The
following chart demonstrates effectiveness of moisture removal under a given vacuum.
COMPOUND GAUGE
READING IN INCHES
OF MERCURY VACUUM
For each 1,000 feet of elevation above sea level, the compound
gauge reading will be about one inch lower, numerically.
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
Figure 21-7. Evacuation Hookup
CHART 2105. SYSTEM VACUUM

System Vacuum

27.99
28.89
29.40
29.71
29.82
29.88
—NOTE—
1G10
Temperature °F.
100
80
60
40
20
0
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Reissued: August 1, 1986