3. Servicing Cooling System
A. Malfunction Detection
NOTE: If the cooling system has leaked refrigerant or is discharged, the compressor oil level must
be checked.
Detection of system malfunction largely depends on the mechanic’s ability to interpret gauge
pressure readings into system problems. A system operating normally will have low side gauge
pressure reading that will correspond with the temperature of the refrigerant evaporating, allowing
for a few degrees temperature rise due to loss in tube walls and fins. The high side will have a
gauge pressure that will corresponds with the temperature of the refrigerant condensing in the
condenser, allowing for a few degrees temperature drop due to loss in tube walls and fins.
Any deviation from that which is normal indicates a malfunction within the system due to faulty
control device, obstruction, defective part, or improper installation.
Detection of system malfunction is made easier with knowledge of the relationship between
temperature and pressure of refrigerant HFC134a. Refer to Chart 2 for specific values.
NO
TE: Gauge readings are about one inch mercury or 1/2 psi higher than chart reads for each
1000 feet elevation above sea level.
Actual air temperature of air passing over the evaporator coils will be several degrees warmer
allowing for a temperature rise caused by the loss in the fins and tubing of the evaporator.
The importance of a seasonal check up of the air conditioning system should be brought to the
attention of the customer whenever possible. A thorough check of the system performed in a
methodical manner will reveal trouble the customer is often not aware of. Locating and repairing the
trouble early will usually result in savings to the customer both in time and additional troubles that
too often result from neglect.
A performance test of the system is the only positive way in which the complete system can be
checked for efficient operation. The air conditioning system should be given this test before work is
begun on the system whenever possible. However, if the system is completely inoperative, repairs
must be performed before the system can be properly tested. The test can uncover further work that
must be performed before the system is brought to its full operating efficiency. The performance test
should always be performed after repair work has been done and before the airplane is released to
the customer. The serviceman performing this test carefully will ensure that the repairs have been
properly performed and that the system will operate satisfactorily.
The performance test, when properly performed includes a thorough examination of the outside of
the system as well as the inside. Many related parts are overlooked because it is felt they are of no
bearing on the operating efficiency of the unit. For this reason, a thorough visual inspection of the
complete system should be performed, followed by an operating inspection of the system.
THE NEW PIPER AIRCRAFT, INC.
PA-32-301FT / 301XTC
MAINTENANCE MANUAL
PAGE 9
Jun 1/03
2C21
21-50-00
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