HEATER THERMOSTAT.-Continued

TM5-4120-384-14

4-33.

H E A T E R THERMOSTAT.-Continued

Disconnect input power from the air conditioner before

performing maintenance on any part of the electrical

The voltages used can be lethal.

system.

Inspect/Test.

(1)

Disconnect

power

source.

(2) (Models F18H-3S and F18H-1S) Remove top front cover

(para

4-11).

(Models F18H-3SA and F18H-3SB) Remove top cover (para

4-11).

(3) (Models F18H-3S and F18H-1S only)

Remove two screws and

lock washers that attach heater thermostat

bracket to top center

cover.

(4) Inspect

for cracks, loose

connections,

and

obvious

Replace

if defective.

damage.

(5)

Tag

and

disconnect

leads.

(6) Using a multimeter check continuity on terminals

Continuity should be indicated.

and

2 of the thermostat.

(7)

Repeat

step

(6)

with

meter

connected

terminals

and

(8) Tape the bulb of a thermometer or junction of a

thermocouple to the body of the heater thermostat, and connect the

multimeter to terminals 1 and 2.

Use a 150 watt lamp bulb or a

heat source.

Gradually apply heat while observing both the

thermometer and the multimeter.

Continuity should drop out at 145

Remove heat source and let the thermostat

to 155F (63 to 68C).

cool while observing the thermostat and multimeter.

Continuity

should be re-established at 100 to 120F (38 to 49C).

(9)

Repeat

step

(8)

with

meter

connected

terminals

and

Replace.

Replace defective heater thermostat by removing

two screws and lock washers that attach thermostat to bracket.

Installation.

(1) See