TM 9-4120-403-14
d. Connect individual pressure gages, or a refrigeration charging manifold and hoses to the high (discharge) and
low (suction) charging valves.
e.
CAUTION
Take care that only a very small amount of refrigerant is allowed to escape during hose purging.
e. Loosen hose connections at gages or charging manifold.
f. Open high (discharge) pressure charging valve slightly to purge air from hose. Tighten low pressure hose
connection at gage fitting as soon as a hissing sound is heard.
g. Open low (suction) pressure charging valve slightly to purge air from hose. Tighten low pressure hose
connection at gage fitting as soon as a hissing sound is heard.
h. Open the low (suction) and high (discharge) charging valves.
i. Both gages should read the same. Check the reading with the appropriate column in table 5-1. If the system is
even partially charged, the pressure should be approximately equal to that shown in the table for the appropriate ambient
temperature. If the pressure is considerably less than shown in the table, the system does not contain enough refrigerant
to continue the pressure check; go to leak testing.
j. Turn the mode selector switch to the COOL mode with the TEMPerature control thermostat in the full
DECREASE setting for a few minutes.
k. With the unit operating, allow gages to stabilize. Take readings of the two gages.
(1) Discharge pressure too high. Possible causes:
Dirty or partially blocked condenser coil. (See para 4-60.)
Partially blocked condenser fan discharge. (See para 4-19.)
Loose or missing lower panel (see para 4-17), Connector coverplate (see para 4-14), or circuit
breaker access plate (see para 4-15).
Overcharge of refrigerant. (See para 5-12.)
Air in refrigerant system. (See para 2-3.)
5-30
