Operation Under Usual Conditions. - TM-5-4110-217-140031

further starting attention. In cold weather, it may be

NOTE

necessary to hand choke the gasoline engine until it

Should the defrost termination control

attains operating temperature. f During the initial cooling

fall, the defrost timer contact will open

cycle when the operating temperature of the box is being

after 30 minutes

lowered to the correct temperature, the box door should

be kept closed and the box should not be loaded until the

The defrost relay is now de-energized and power is

operating temperature is constant.

switched from the hot gas solenoid to the liquid solenoid

and magnetic fan clutch through the time delay circuit.

2-12.

Operation Under Usual Conditions.

The refrigerant now starts flowing through the

refrigeration cycle and the evaporator/condenser fans

start moving as the time delay circuit closes.

a. For normal operation of the unit, head pressure

d. Automatic defrosting occurs after 4 hours of the

on the refrigerating unit must not be so high as to trip the

unit operation. Manual defrosting can be activated by

high pressure cutout switch. Defrosting of the unit is

pushing the "MANUAL DEFROST" switch on the control

automatic.

panel. Automatic defrost will resume after completion of

b. A defrost cycle is activated automatically at a

a manual defrosting cycle.

preset running time interval by the advancement of the

e. Defrost should take about 20 minutes. Inspect

defrost timer motor. When the timer contact is closed,

evaporator coil for frost removal after manual defrost is

the defrost relay is energized and switches the power

completed.

from liquid solenoid and magnetic fan clutch to the hot

gas solenoid. Hot gas starts to flow through the hot gas

2-13.

Stopping the Equipment.

coil and defrost occurs.

c. Defrosting continues until the defrost

termination control opens on temperature rise of the

a. Move the ON-OFF switch to the OFF position

evaporator coil.

to stop the refrigeration unit (fig. 2-3).

b. Perform the daily preventive maintenance

services (para 3-6).

Section II. OPERATION UNDER UNUSUAL CONDITIONS

c. Inspect condenser frequently. Dirt or dust

2-14.

Operation in Extreme Cold (Below 0F).

accumulating on condenser tubes or fins causes

a. Keep batteries fully charged.

increased discharge pressure. If tubes and fins are

b. Keep fuel tank full at all times.

coated, clean with brush, clean cloth, or compressed air.

c. Drain and service the fuel filter (para. 3-25).

d. Keep covers on all controls and wiring.

d. Lubricate in accordance with the current

e. Check engine oil frequently for cleanliness.

lubrication chart.

f. Check air filter frequently for cleanliness.

2-15.

Operation in Extreme Heat.

2-17.

Operation

Under

Rainy

Humid

a. Lubricate engine in accordance with current

Conditions.

lubrication chart.

b. If carburetor floods when attempting to start

a. Inspect evaporator coil frequently. In humid

engine, open throttle wide, open choke and turn engine

areas the evaporator coil rapidly collects frost. Any

crankshaft over several times, If vapor lock is evident, do

steady drop in the compound pressure gage reading

not attempt to start engine for 15 minutes.

generally indicates that the evaporator needs defrosting.

c. Check dial thermometer on refrigeration unit

b. Read dial thermometer frequently to check

frequently to ascertain proper operation of the unit.

proper operation of the unit.

d. Increase frequency of periodic inspection and

c. Increase frequency of periodic Inspections and

maintenance operations.

d. Check engine oil level frequently.

e. High moisture content in the air will cause

2-16.

Operation in Dusty or Sandy Areas.

difficulty in the electrical system. The spark plug,

magneto, and wiring may become unserviceable

a. Clean refrigeration unit frequently.

b. Remove dirt or dust that accumulates on the

condenser or evaporator fans and housings.

Change 3 2-7