SERVICE - TM-5-4120-393-140240

TM 5-4120-393-14

5-15. Refrigerant Pressure Check (cont)

Open the low (suction) and high (discharge) service valves.

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. See para 5-12.

Turn the mode selector switch to the COOL mode with the TEMPerature control thermostat in the full DECREASE

setting for a few minutes.

With the unit operating, allow gages to stabilize. Take readings of the two gages

(1) If the discharge and suction pressures are at, or near, the same value, a pressure equalizer solenoid valve

malfunction or an internal compressor failure is indicated.

(2) If discharge pressure is low and suction pressure is normal, (see table 5-2), a low refrigerant charge is

indicated.

(3) If discharge pressure is normal and suction pressure is either hi gh or low, failure or maladjustment of the

pressure regulator valve or expansion valve is indicated.

(4) If discharge pressure is high and suction pressure is normal, a malfunction of the condenser fan, refrigerant

overcharge, or clogged filter drier is indicated.

When pressure tests are completed, proceed with the maintenance action indicated.

Turn unit OFF.

Close both service valves on unit.

m. Remove gages or service manifold hoses from service valves.

Install the valve stem and hose connection protective caps.

5-34 Change 1