Section IV. GENERAL REPAIR INSTRUCTIONS

TM 5-4120-274-15

Warning: Avoid bodily contact with liq-

(4) Install junction and control box, refer

uid refrigerant and avoid inhaling refrigerant

to paragraph 3-28.

gas Be especially careful that the R-22 refrig-

erant does not contact the eyes. In case of re-

(5) Install front access panel, refer to para-

frigerant leaks ventilate area immediately.

graph 3-18.

Section IV. GENERAL REPAIR INSTRUCTIONS

static switch. The energized contactor supplies

5-18. General

power to the compressor through the normally

The air conditioner, after it is started is auto-

closed contacts of the circuit breaker and the com-

matic in operation. The relationship of the auto-

pressor overload protector. After the fan motor

matic components, controls, and instruments, is

and compressor have started, the operation of the

explained in the operation analysis for mainte-

refrigerant unit is controlled by the thermostat.

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

Sensing a rise in the air temperature above the set

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

point, the thermostat opens its contacts, de-ener

wiring diagrams (fig. 1-5), are included to as-

gizing the liquid line solenoid valve. This po-

sist in the maintenance of the electrical compo-

sitions the valve for cooling service. Sensing a fall

nents, wiring harness, wire leads, and refrigerant

in the air temperature below the set point, the

components.

contacts of the thermostat close, energizing the

valve. This positions the system for bypass service.

Figure 5-1. Refrigerant flow diagram

(Located in back of manual)

(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

to observe this warning may result in injury to

(1) The fan motor and compessor run con-

personnel and damage to the equipment.

tinuously, whether the thermostat is calling for

cooling or not, when the unit is set operate on

5-19. Analysis of Operation

the cooling cycle of operation. This feature pro-

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

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

(2) Bypass cycle of operation. When the

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

conditioned air temperature falls below the ther-

2-3).

mostat setting, the circuit which controls the sole

(1) When the selector switch is in the OFF

noid valves is energized causing:

position the entire circuit is dead.

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

(2) Placing the selector switch in the HI-

charge gases through the evaporator pressure

HEAT position actuates the fan motor with all

regulator bypassing a major part of the com-

six heater elements being under the control of the

passed refrigerant vapor directly back to the suc-

thermostat. If the air temperature falls below the

tion side of the compressor.

set point of the thermostat the control contacts

close, energizing the evaporator contactor which

(b) To prevent f rest from forming on the

supplies power to the heaters through the nor-

evaporator, a back pressure regulating valve is

mally closed contacts of the evaporator heater

provided to prevent the suction pressure from-

thermostat.

creasing to a pressure of 58 psig which corre-

(3) Moving the selector switch to the LO-

spends to a temperature of less than 32 degrees

HEAT position presents the same control se-

F. (Fahrenheit).

quence but reduces the heating capacity of the

d. Heating Operation. Placing the selector

unit by supplying power to threw of the heater

switch in the LO-HEAT postinactuates half of

elements only.

the evaporator heatrs mounted, in the condition-

(4) The fan motor starts when the selector

ed air stream directly behind the evaporator

switch is placed in the VENTILATE position.

coil. When the selector switch is placed in the

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

HI-HEAT position, the remaining heaters are en-

in operation and the compressor motor contactor

ergized, providing maximum heating capacity.

is energized through the contacts of the thermo-

5-3