Malfunction Detection - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
14-90. MALFUNCTION DETECTION.
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The detection of system malfunction largely depends on the mechanic's ability to relate the gauge
pressure readings to 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 1 2 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 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.
Reissued: 9/23/80
ACCESSORIES AND UTILITIES
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