SERVICING COOLING SYSTEM
MALFUNCTION DETECTION
A normally operating system will have a low side gauge pressure reading corresponding with refrigerant
temperature in the evaporator, allowing for a few degrees temperature rise due to loss in tube walls and fins.
The high side will have a gauge pressure corresponding with refrigerant temperature in the condenser,
allowing for a few degrees temperature drop due to loss in tube walls and fins.
Any deviation from normal indicates a system malfunction due to a faulty control device, obstruction,
defective part, or improper installation.
Temperature and pressure of Refrigerant 12 is in close proximity with pressures of twenty and eighty
pounds per square inch (psi). The temperature-pressure chart shows that there is only a slight variation
between temperature and pressure of refrigerant in lower range.
For every pound of pressure added to low side, a temperature increase of about one degree Fahrenheit
takes place. For instance, a pressure of 23.8 on 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. Actual temperature of air passing over
coils of evaporator will be several degrees warmer allowing for a temperature rise caused by loss in fins and
tubing of evaporator.
—NOTE—
For each 1,000 feet of elevation above sea level, gauge readings
will be about one inch of mercury or 1/2 psi higher than chart
indicates.
A performance test of the system is the only way to test the complete system for efficient operation. This
test should be performed before work is begun on the system. If the system is completely inoperative, repairs
must be done before the system can be tested. Always performance test system before returning aircraft to
service. A good performance test includes a visual inspection followed by an operational inspection of the
system.
21 - 52 - 00
Page - 21 - 11
Reissued: August 1, 1986
1G1
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
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