TM 9-4120-388-14
5-13. REFRIGERANT PRESSURE CHECK - Continued.
(3) Suction pressure too low.
Possible causes:
(a) Dirty return air filter.
(b) Partially blocked discharge or return air ducts or openings.
(c) Dirty evaporator coil.
(d) Cold return air.
(e) Low refrigerant charge.
(f) Liquid solenoid valve closed.
(g) Fan motor not operating.
(h) Evaporator fan loose on motor shaft.
(i) Problem with expansion valve operation.
(j) Expansion valve superheat too high.
(k) Plugged or kinked distributor tube.
(l) Suction line or evaporator coil tubing restriction.
(m) Clogged dehydrator (filter-drier).
(n) Moisture in refrigerant system.
(4) Suction pressure too high.
Possible causes:
(a) High return air temperature.
(b) Open equalizing solenoid valve.
(c) Compressor not running.
(d) Expansion valve bulb damage or poor contact with suction line.
(e) Internal compressor failure.
(f) Problem with Iiquid quench expansion valve.
(g) Problem with regulating valve.
(h) Problem with expansion valve.
k. When pressure tests are complete, proceed with the maintenance action indicated.
l.
Turn unit OFF.
m. Close service valves on unit.
n.
Remove gages or service manifold hoses from service valves.
Install service valve protective caps.
o.
p. Secure service valve access cover with four screws and flat washers.
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