TM 9-4120-407-14
Table 4-3. Normal Operating Pressures (In Full Cooling Decrease Mode)
Pressure Range (Psig)
Temperatures
120 F (49 C)
100 F (38 C)
75 F (24 C)
Outdoor ambient
50 F (10 C)
75-98 Suction
60-75 Suction
59-70 Suction
55-65 Suction
90F (32 C) Return
Air to
370-430 Discharge
275-350 Discharge
175-210 Discharge
125-160 Discharge
Air Conditioner
(Dry Bulb)
65-90 Suction
60-75 Suction
58-70 Suction
80 F (27 C) Return
58-65 Suction
Air to
370-410 Discharge
275-325 Discharge
170-205 Discharge
120-155 Discharge
Air Conditioner
(Dry Bulb)
(4) With the Air Conditioner operating, allow gauges to stabilize. Take readings of the two gauges
and compare to Table 4-3.
(a) If discharge and suction pressures are at, or near, the same value, a pressure equalizer solenoid
valve (L1) or compressor failure is indicated.
(b) If discharge pressure is low and suction pressure is normal, a low refrigerant charge is
indicated.
(c) If discharge pressure is normal and suction pressure is either high, or low, failure or
maladjustment of the expansion valve is indicated.
(d) If ice forms on evaporator coil or evaporator coil does not cool during operation, failure or
malfunction of evaporator expansion valve is indicated.
(e) If discharge pressure is high and suction pressure in normal, refrigerant overcharge is
indicated.
(5) When pressure tests are completed, turn Air Conditioner off and proceed with any maintenance
action indicated.
(6) Turn rotary MODE selector switch to OFF RESET.
NOTE
FOLLOW-ON MAINTENANCE:
Remove service manifold. See para 4-11.
4-49
