TM 9-4120-388-14
5-13. REFRIGERANT PRESSURE CHECK - Continued.
Connect individual pressure gages, or a refrigeration charging manifold and hoses to the high (discharged) and
d.
low (suction) service valves.
Take care that only a very small amount of refrigerant is allowed to escape during
Loosen hose connections at gages or charging manifold.
e.
f.
Open high (discharge) pressure service valve slightly to purge air from hose. Tighten high pressure hose con-
nection at gage fitting as soon as a hissing sound is heard.
Open low (suction) pressure service valve slightly to purge air from hose. Tighten low pressure hose connection
g.
at gage fitting as soon as a hissing sound is heard.
h.
Open the low (suction) and high (discharge) service valves.
i.
Both gages should read the same. Check the reading with the appropriate column in Table 5-2. If the system
is even partially charged, the pressure should be approximately equal to that shown in the table for the appropri-
ate ambient temperature. If the pressure is considerably less than shown in the table, the system does not con-
tain enough refrigerant to continue the pressure check; go to leak testing.
Turn the mode selector switch to the COOL mode with the TEMPerature control thermostat in the full DE-
j.
CREASE setting for a few minutes.
(1) Discharged pressure too high.
Possible causes:
(a) Dirty or partially blocked condenser coil.
(b) Partially blocked condenser fan discharged.
(c) Loose or missing lower front panel, connector cover plate, circuit breaker access cover, or filter mount-
ing plate.
(d) Excessive recirculation of hot condenser discharge air back into condenser intake.
(e) Overcharge of refrigerant.
(f) Air in refrigerant system.
(g) High suction pressure - See (4) below.
(h) Fan motor not operating.
(i)
Condenser fan loose on shaft.
(j) Too much oil in refrigerant system.
(2) Discharge pressure too low.
Possible causes:
(a) Cold outside air.
(b) Low refrigerant charge.
(e) Problem with pressure regulating valve.
(f)
5-28