Diagnosing Refrigeration System Problems

TM 10-4110-262-13&P

0028 00

Diagnosing Refrigeration System Problems

Test Procedure

1. Operate the unit in cooling mode.

2. Maintain discharge pressure at 290 to 310 psig. Control condenser air flow to maintain discharge

pressure.

3. Maintain box temperature near 0 F (-18 C).

4. Record suction pressure. Normal reading is 12 - 20 psig.

5. Check the suction line at the accumulator.

NOTE

A cool, moist line is normal. A frosted or abnormally dry line and out-of-

range pressures indicate refrigeration problems.

Select Appropriate Suction Line Condition and Suction Pressure Category Below

1. LOW SUCTION PRESSURE-FROSTED SUCTION LINE

Basic Problem:

Insufficient Evaporator Air Flow

a. Evaporator coil iced.

b. Evaporator airflow restricted (dirty coil, plugged air inlets, etc.).

Evaporator fan motor failure.

2. LOW SUCTION PRESSURE-UNFROSTED SUCTION LINE

Basic Problem:

Insufficient Refrigerant Flow

a. Low refrigerant charge,

b. Expansion valve screen restricted (if equipped).

Restricted drier.

d. Leaking expansion valve bulb/tube.

e. Restricted suction pressure regulator.

Frozen expansion valve.

0028 00-5