Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 167 / 881

MALFUNCTION DETECTION.
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 the knowledge that the temperature and pressure of
Refrigerant 12 is in close proximity between the pressures of twenty and eighty pounds per square inch (psi). A
glance at the temperature pressure chart 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 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 aircraft is released to the customer. The serviceman performing this test carefully will insure 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.
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
2 1 - 5 1 - 0 3
Page 21-56
Revised: May 15, 1989
1G23
PIPER AIRCRAFT