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TM5-4120-376-14
5-14. PRESSURE TESTING. Pressure testing the refrigeration system is an important
diagnostic procedure which you should perform whenever the system has been newly recharged
after replacement of a component or when the air conditioner is operating inefficiently.
Pressure testing is accomplished by connecting individual pressure gauges or a refrigeration
manifold gauge to the suction and discharge service valves. Compare readings to Table 5-2.
a. Set Up. Prepare the air conditioner for pressure-testing as stated below.
(1) Make sure that the fresh air damper is completely closed and that the evaporator
louver (inlet) and evaporator (discharge) are fully open.
(2) Hang an accurate thermometer directly in front of the evaporator louver (inlet) to
record dry bulb return air temperature to the unit.
(3) Hang an accurate thermometer directly in front of the condenser coil guard, making
sure that the thermometer is shaded from direct sun light, to record “outdoor ambient
temperature”.
(4) Connect a refrigeration service manifold gauge to the suction and discharge service
valves, purging the manifold of any air trapped in the lines.
(5) If indoor ambient temperature is too low, provide a space heater to raise the dry bulb
return air temperature to 80°F (27°C).
b. Procedure. Perform the pressure test in the following manner:
(1) Turn the mode selector to COOL, and the temperature selector to maximum
COOLER.
(2) Slowly open the suction and discharge service valves to which pressure gauges have
been connected.
(3) Let the air conditioner operate for at least 15 minutes in the cooling mode, so that all
parts of the system are stabilized.
(4) Record the temperatures indicated by both thermometers and the pressures indicated
by both pressure gauges.
(5) Compare the readings obtained from pressure testing with the normal ranges shown in
Table 5-2.
c. Analysis of Discrepancies. If actual pressure-temperature relationships differ from those
shown in Table 5-2, consider the following reasons, and take appropriate action.
(1) If pressures are too low: Check leaks in accordance with paragraph 5-11. Repair and
recharge the system in accordance with paragraph 5-13 and repeat the pressure test paragraph
5-14.
(2) If pressures are too high: Close the suction service valve, remove the pressure gauge,
and bleed off the appropriate amount of refrigerant in accordance with Table 5-2. Repeat the
pressure test 5-14.
5-18
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