Heater Thermostat

resistance (should read-zero ohms) between the

banks of the heating elements are energized if the

associated normally closed contacts. The resistance

control thermostat is, set above evaporator return

between the normally open contacts should read

air temperature.

infinity on the ohmmeter. Then apply minimum

b. Testing. Refer to figure 1-5 and, using an

rated test voltage to relay coil. Contacts must

ohmmeter, measure resistant; between terminals A

r e v e r s e from open to closed as noted by a clicking

and B. Meter should read approximately 10 ohms.

noise. Finally, measure the contact resistance with

Next, measure resistance between heater terminals

t h e relay energized, The ohmmeter readings should

and casing. Must read open circuit ohms.

b e infinite for the normally closed contacts and zero

c. Removal.

ohms for the normally open contacts. Check for

(1) Remove the top panel (para 4-11).

resistance from each of the terminals to the case of

( 2 ) Remove the nuts and washers securing the

the air conditioner. Open circuit resistance should

w i r i n g to the heating elements and tag and remove

the wiring.

be indicated.

c. Removal.

( 3 ) Loosen the retaining screw and remove the

clamp which secures the heater to the heater

(1) Remove the top panel (para 4-11).

support bar.

(2) Tag and disconnect the ten wire leads.

(4) Lift the heating element out of the air

(3) Remove the two nuts, washers and screws

conditioner.

and remove the relay.

d. Installation. Installation should be per-

d. Installation. Installation shall be in the

f o r m e d in reverse order of removal. Be sure that all

reverse order of removal.

wiring is reconnected properly and that all con-

4-53. Wiring Harnesses

nections are tight. Keep wiring terminals oriented

a. Function. There are six wiring harnesses

so that shorts do not occur across the heater ter-

included in the air conditioner which serve to

minals.

distribute the power and control wiring to the

4-51.

Heater Thermostat

various electrical components included. In addition

to these harnesses there are thirty-nine individual

a. Function. The heater thermostat protects the

electrical leads which are not integral to the

air conditioner from overheating when in the

aforementioned harnesses. Two harnesses and

heating mode. It cuts off the power supply to all

twenty-seven electrical leads are included in the

heating elements upon a rise to a temperature of

90 5 C. This situation should normally only

junction box assembly. One harness and three

electrical leads are included in the control panel

o c c u r in the absence of air flow across the heating

assembly. Three harnesses and nine electrical leads

elements.

are included in the air conditioner outside the

b. Testing. Using an ohmmeter check for

control panel and junction box.

continuity between the three terminals of the

b. Inspection and Test. Inspection and test of

thermostat. There should be zero resistance across

the wiring harnesses consists of visually checking

each pair of terminals. Check for resistance from

f o r broken or cracked insulation, poor solder joints

each of the terminals to the case of the air con-

or loose terminal connections. Proper operation of

ditioner. Open circuit resistance should be in-

t h e air conditioner in all modes of operation is the

dicated.

c. Removal.

b e s t check of the various wiring harnesses. Refer to

F i g u r e Numbers 1-5 and 1-7 in the event there is a

(1) Remove the top panel (para 4-11).

malfunction in the operation of the air conditioner

( 2 ) Tag and remove the three wire leads from

for electrical check points. Use a multimeter to

the heater thermostat.

check for continuity from point to point and to

(3) Remove the two screws, nuts and washers

which secure the heater thermostat to the heater

check for shorts between connections.

c. Removal.

support bar and remove the thermostat.

d. Installation. Installation shall be in the

(1) P o w e r d i s t r i b u t i o n w i r i n g h a r n e s s .

reverse order of removal.

(a) Remove the junction box (para 4-36).

(b) Remove the top panel (para 4-11).

4-52. Fan Speed Relay

a . Function. This relay is used to control the fan

from capacitors C1 and C2. Tag the wires before

speed as selected by the fan speed switch on the

disconnecting.

control panel or the fan speed control pressure

(d) Disconnect P7 from connector J7 on the

s w i t c h which closes upon an increase in refrigerant

top portion of the evaporator/ condenser partition,

pressure. This relay is a four pole double throw type

P3 from connector J3 on the compressor and P10

w i t h four normally open contacts and four normally

from J10 on the junction box.

closed contacts.

(e) R e m o v e t h e t w o s c r e w s , s p a c e r s a n d

b. Testing. U s e a n o h m m e t e r a n d m e a s u r e

4-16