Piper Aircraft Corporation Malibu Mirage PA-46-350P, Airplane Maintenance Manual

Page: 327 / 1956

PAGE 9
Feb 28/07 2E1
21-50-00
PIPER AIRCRAFT, INC.
PA-46-350P, MALIBU MIRAGE
MAINTENANCE MANUAL
C. Malfunction Detection
NOTE: If the cooling system has leaked refrigerant or is discharged, the compressor oil level must
be checked.
The detection of system malfunction largely depends on the mechanic’s ability to interpret the
gauge pressure readings into system problems. A system operating normally will have a low side
gauge pressure reading that will correspond with the temperature of the refrigerant evaporating in
the evaporator, allowing for a few degrees temperature rise due to loss in the tube walls and fins.
The high side will have a gauge pressure that will correspond with the temperature of the refrigerant
condensing in the condenser, allowing for a few degrees temperature drop due to loss in the tube
walls and fins.
Any deviation from that which is normal indicates a malfunction within the system due to a 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 the refrigerant (R-12 or HFC-134a). They are in close proximity
between the pressures of twenty and eighty pounds per square inch (psi). A glance at the
temperature-pressure chart (i.e. - Chart 2) will show that there is only a slight variation between the
temperature and pressure of the refrigerant in the lower range.
It is correct to assume that for every pound of pressure added to the low side, a temperature
increase of about one degree Fahrenheit takes place. For instance, a pressure of 23.8 on the chart
indicates a temperature of 24°F. A change of pressure of almost one pound to 24.6 psi gives us a
temperature increase to 25°F.
NOTE: For each 1,000 feet of elevation above sea level, the gauge readings will be about one inch
of mercury or 1/2 psi higher than the chart indicates.
It must be pointed out that the actual temperature of the air passing over the coils of the evaporator
will be several degrees warmer than the fins, 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.