TM 9-4120-357-14
TABLE 5-1.
TROUBLESHOOTING (Cont)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
Step 3.
Check compressor for noisy operation, high suction pressure, or excessively low discharge pressure, in-
dicating leaky internal valves.
Replace compressor and recharge system.
5.
COMPRESSOR EXCESSIVELY NOISY.
Step 1.
Listen for knocking or hammering sounds. Install gauge set, and check for high discharge pressure indi-
cating that liquid refrigerant is returning to compressor.
Shut down at once. Replace faulty expansion valve.
Step 2.
Install gauge set and check for high discharge pressure, indicating overcharge of refrigerant or presence
of air or other non-condensible gas in system.
Bleed refrigerant gas from system over a period of 5-6 hours to prevent blowing oil out of system.
Purge system with dry nitrogen, replace drier-strainer, evacuate and recharge.
6.
SUCTION PRESSURE TOO LOW OR TOO HIGH
Step 1.
Stop compressor and check thermostatic expansion valve as follows:
a. Remove insulating compound from remote bulb, and remove bulb from refrigerant line.
b. Place bulb in ice water for 1-2 minutes.
c. Start compressor.
CAUTION
Do not let liquid flood back into compressor for more than 2-3 sec-
onds or the compressor will be seriously damaged.
d. Remove bulb from ice water and hold it on one hand to warm it. At the same time, start the
compressor and feel the suction line for a rapid change of temperature, which indicates flood-through
of liquid refrigerant. If liquid floods through valve, it is operating satisfactorily. If not, valve or remote
bulb is faulty.
Discharge refrigerant from system over a period of 5-6 hours to prevent blowing oil out of system.
Replace faulty expansion valve and drier-strainer. Purge with dry nitrogen and recharge.
Step 2.
Feel drier-strainer for temperature difference.
Discharge end will feel cooler than input end if clogged,
or discharge end may be sweaty or frosty.
Discharge refrigeration system over a period of 5-6 hours to prevent blowing oil out of system. Re-
place drier-strainer, purge with dry nitrogen, and recharge.
5-6
