Section III TECHNICAL PRINCIPLES OF OPERATION

TM 5-4110-234-14

TO 40R7-5-7-1

Section III TECHNICAL PRINCIPLES OF OPERATION

Para.

Air Flow ...........................................................1-8

Defrost Cycle ........................................................ 1-10

Operational Cycle ............................................1-9

1-8. AIR FLOW

a. Condenser. The condenser fan draws ambient (outdoor) air through the condenser coil and expels it through

top and side screens of refrigerator unit. This removes heat from the refrigerant passing through the coil.

b. Refrigerated Air (Air Inside Enclosure). The evaporator fan draws air through the evaporator coil and expels it

through the top of the evaporator housing. This results in enclosure air losing its heat to the refrigerant passing through

the tubes of the evaporator coil.

1-9. OPERATIONAL CYCLE See figure 1-4.

a. The electric motors (F10000R-6) or the gasoline engine (F10000RG-2) start automatically when the unit thermostat

calls for cooling. This supplies power to the compressor and fans. On the F10000RG-2 only solenoid valve (item 24)

opens during start up allowing the compressor to start with no refrigerant load.

b. The compressor (item 18) converts the low pressure gas refrigerant from the evaporator section to high pressure gas

and sends it to the condenser coil (item 1).

(1) The high pressure refrigerant gas is cooled by ambient air flow across the condenser coil (item 1) and

condenses to liquid which is stored in receiver tank (item 3).

(2) The liquid refrigerant then passes through a filter-drier (item 5) and liquid indicator sight glass (item 6) into heat

exchanger (item 7).

(3) The expansion valve (item 8) regulates flow and reduces pressure so that the liquid refrigerant enters the

evaporator (item 10) as a cold, low pressure liquid.

(4) The refrigerant absorbs heat from enclosure air being drawn over and around evaporator coil (item 10).

(5) The refrigerant evaporates to a low pressure gas which is drawn to compressor inlet.

(6) The cycle repeats until the thermostat requirements are met.

1-10. DEFROST CYCLE

To prevent an excessive buildup of frost and ice on the evaporator coil, this refrigeration unit is equipped with an

automatic defrost cycle. See figure 1-4.

a. Defrost activating mechanism.

(1) The F10000R-6 is equipped with a timing mechanism which can be set for a 45 minute defrost cycle to occur

at any convenient time within each 24 hour period. This control is equipped with a temperature sensor that will stop the

defrost cycle prior to the 45 minute setting if a temperature of 43 2F (6 1C) is reached at the sensor location.

(2) The F10000RG-2 is equipped with a preset timing device that activates the defrost cycle every 12 hours. The

defrost cycle will shut off when a temperature of 45 4F (7 2C) is reached at the sensor location.

b. The timer opens the hot gas solenoid (23) allowing the hot refrigerant gas to be pumped through the drain pan coil

(11) and the evaporator coil (10).

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