Evacuating The System; System Vacuum Chart; Leak Check - Method 11 - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
h.
Add oil, if required. (Refer to Table XIV-XII, paragraph 14-103) then repeat steps a thru e.
i.
If no further leads are found, the system may be evacuated and charged. (Refer to paragraphs 14-99
and 14-100.)
14-98. LEAK CHECK - METHOD II.
a.
Remove the protective cap on the Schrader valve fitting on the suction line valve (on left side of
fire wall), and connect a charging hose with a shutoff valve arrangement to the fitting. The charging hose
must have Schrader fitting or adapter to fit the valve.
b.
Connect the other end of the charging hose to a small cylinder of refrigerant and purge the hose
by allowing a slight amount of refrigerant gas to escape from the Schrader valve fitting.
c.
The cylinder of refrigerant should be placed upright in a container of warm (125 F max.) water
on a small scale.
d.
Allow approximately 1/2 pound of refrigerant to enter the system by opening the valve on the
charging hose and observing the weight change on the scale.
e.
Using an electronic leak detector, check all joints and repair any leaks.
f.
After completion of repair of any leaks, proceed to check the system in accordance with one of
the methods outlined for any other leaks.
g.
If no further repair is required on the system, it is now ready to evacuate in accordance with'
paragraph 14-99.
14-99 EVACUATING THE SYSTEM. If the system has been operated in a discharged condition or any time
the system has been open to atmospheric pressure, the receiver-dehydrator must be replaced and the system
evacuated to remove any trapped air and moisture which has entered it. A vacuum pump capable of pulling 29
inches of mercury or better should be used. As we lower the pressure in the air conditioning system. we lower
the boiling temperature of the water (moisture) that may be present. Then we are able to pull this water, in the
form of vapor, out of the system. The receiver-dehydrator must be changed at least once every two years. The
following table demonstrates the effectiveness of moisture removal under a given vacuum.
TABLE XIV-XI. SYSTEM VACUUM CHART
System Vacuum
Temperature F.
27.99
100
°
COMPOUND GAUGE
28.89
80
READING IN INCHES
29.40 60
OF MERCURY VACUUM
29.71
400
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.
The following steps should be of help when performing this operation:
a.
Remove the cowling from the right engine. (Refer to Section VIII.)
CAUTION
Ascertain that all system pressure is released before attempting the
evacuation. (Refer to paragraph 14-90.)
Reissued: 9/23/80
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ACCESSORIES AND UTILITIES
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