Figure 21-7. Evacuation Hookup
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.
CHART 2105. SYSTEM VACUUM
System Vacuum Temperature °F.
27.99 100
COMPOUND GAUGE 28.89 80
READING IN INCHES 29.40 60
OF MERCURY VACUUM 29.71 40
29.82 20
29.88 0
—NOTE—
For each 1,000 feet of elevation above sea level, the compound
gauge reading will be about one inch lower, numerically.
21 - 52 - 00
Page - 21 - 20
Reissued: August 1, 1986
1G10
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
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