Section IV. GENERAL REPAIR INSTRUCTIONS

TM 5-4120-273-15

Warning: Avoid bodily contact with liquid

(4) Install junction and control box, refer-

refrigerant and avoid inhaling refrigerant gas.

ence paragraph 3-28.

Be especially careful that the R-22 refrigerant

does not contact the eyes. In case of refrigerant

(5) Install front access panel, reference

leaks ventilate area immediately.

paragraph 3-18.

Section IV. GENERAL REPAIR INSTRUCTIONS

tor is energized through the contacts of the ther-

5-18. General

mostatic switch. The energized contactor supplies

The air conditioner, after it is started, is auto-

power to the compressor through the normally

matic in operation. The relationship of the auto-

closed contacts of the circuit breaker and the com-

matic components, controls, and instrument, is

pressor overload protector. After the fan motor

explained in the operation analysis for mainte-

and compressor have started, the operation of the

nance of the air conditioner (para 5-17). A re-

refrigeration unit is controlled by the thermostat.

frigerant flow diagram (fig. 5-1) and practical

Sensing a rise in the air temperature above the set

wiring diagram (fig, 1-5) are included to assist

point, the thermostat opens its contacts, de-ener-

in the maintenance of the electrical components,

gizing the liquid line solenoid valve. This posi-

wiring harness, wire leads, and refrigerant com-

tions the valve for cooling service. Sensing a fall

ponents.

in the air temperature below the set point, the con-

Figure 6-1. Refrigerant flow diagram

tacts of the thermostat close, energizing the valve.

(Located in back of manual)

This positions the system for the bypass service.

(6) The HI-LO fan speed switch controls the

Warning: Disconnect the air conditioner from

speed of the fan motor and the fans.

the power source before performing any main-

b. Cooling Cycle of Operation.

tenance on the components of the unit. Failure

(1) The fan motor and compressor run con-

to observe this warning may result in injury

tinuously whether the thermostat is calling for

to personnel and damage to the equipment.

cooling or not, when the unit is set to operate on

the cooling cycle of operation. This feature pro-

5-19. Analysis of Operation

vides a constant electrical load thus preventing

a. General. The type and degree of air condi-

voltage fluctuations within the system.

tioning provided by the unit is controlled by a

(2) Bypass cycle of operation. When the

five-position selector switch (fig. 2-3), a thermo-

conditioned air temperature falls below the ther-

stat (fig. 2-3), and a hi-lo fan speed switch (fig.

mostat setting, the circuit which controls the sole-

2-3).

noid valve is energized causing:

(1) When the selector switch is in the

(a) The hot gas bypass line to flow dis-

"OFF" position the entire circuit is dead.

charge gases through the evaporator pressure

regulator, bypassing a major part of the com-

(2) Placing the selector switch in the HI-

pressed refrigerant vapor directly back to the

HEAT position actuates the fan motor with all

suction side of the compressor.

six heater elements being under the control of the

(b) To prevent frost from forming on the

thermostat. If the air temperature falls below the

evaporator, a back pressure regulating valve is

set point of the thermostat, the control contacts

provided to prevent the suction pressure from de-

close energizing the evaporator contactor which

creasing to a pressure of 58 psig which corre-

supplies power to the heaters through the nor-

sponds to a temperature of 32F.

mally closed contacts of the evaporator heater

d. Heating Operation. Placing the selector

thermostat.

switch in the LO-HEAT position actuates half of

(3) Moving the selector switch to the LO-

the evaporator heaters mounted, in the condi-

HEAT position presents the same control se-

tioned air stream, directly behind the evaporator

quence but reduces the heating capacity of the

coil. When the selector switch is placed in the HI-

unit by supplying power to three of the heater ele-

HEAT position, the remaining heaters are ener-

ments only.

gized, providing maximum heating capacity.

(4) The fan motor starts when the selector

switch is placed in the "VENTILATE" position.

5-20. General Repair Procedures

(5) In the "COOL" position, the fan motor

a. If the refrigerant system must be opened for

is in operation and the compressor motor contac-

repair or replacement of parts, first discharge the

5-3