System Losing Cooling Capacity

TM 5-4120-355-14

LITTLE OR NO HEATING CAPACITY

Step 1. Wiring and wiring harneess may be defective.

Replace defective wiring (para 5-1 O).

Step 2. Check heater elements for continuity.

Redate defective element.

5-5. System Losing Cooling Capacity

If the system is losing cooling capacity, or is in some way not functioning properly, a check of system operating

pressure will frequently lead to the cause of malfunction. Install pressure gages on access fittings of suction and discharge

lines and expose gages to system pressure. Compare gage readings with normal ranges of systems pressures listed in table

4-2.

Table 4-2. Normal Operating Pressures

Return air

to unit

80 F/67 F WB

80 F/75 F WB

Outdoor ambient

120F

125F

95 F

GAGE

PRESSURE

suction

85-95

70-80

87-97

Discharge

387-395

406-416

253-263

Section Ill. General Maintenance

58. General

The air conditioner, after it is started, is automatic in operation. The relationship of the automatic components,

controls, and instruments, is explained in the operational analysis for maintenance of the air conditioner (Para 57). A

refrigerant piping diagram (fig. 51) and practical wiring diagram (fig. 1-3), are included to assist in the maintenance of the

electrical components, wiring harness, wire leads, and refrigerant components.

Figure 51. Refrigerant flow diagram. (Located in back of manual).

57. Analysis of Operation

a. General. The type and degree of air conditioning provided by the unit is controlled by a five position selector

switch (fig. 4-2A), a thermostat, and a hi-lo fan speed switch.

(1) When the selector switch is in the OFF position, the entire circuit is dead except the crankcase heater.

(2) Placing the selector switch in the H l-HEAT position actuates the fan motor with all six heater elements

being under the control of the thermostat. If the air temperature falls below the set point of the thermostat, the control

contacts close, energizing the evaporator contractor which supplies power to the heaters through the normally closed con-

tacts of the evaporator heater thermostat.

(3) Moving the selector switch to the LO-HEAT position presents the same control sequence but reduces the

heating capacity of the unit by supplying power to three of the heater elements only.

5-3