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8–44
2. To check the defrost air switch, run unit in cool-
ing and jumper across the air switch terminals.
This will start the defrost cycle as it simulates
the action of the defrost air switch. Bypassing
the switch in this manner operates all compo-
nents involved in defrost.
3. Unit should remain in defrost until the DTT and
SAT both reach 55°F (12.8°C). At this point the
defrost cycle will terminate, and the unit will
resume automatic operation.
4. If the above test indicates satisfactory operation,
test DAS settings using a Magnehelic gauge
(Carrier Transicold part number 07-00177) or
similar instrument as follows.
5. Ensure magnehelic gauge is in proper calibra-
tion.
NOTE
The magnehelic gauge may be used in any
position, but must be re-zeroed if position of
gauge is changed from vertical to horizontal
or vice versa. USE ONLY IN POSITION
FOR WHICH IT IS ZEROED.
6. With air switch in vertical position, connect high
pressure side of magnehelic gauge, a tee and
aspirator to high side connection of air switch.
Tee is to be placed approximately half-way
between gauge and air switch or an improper
reading may result. (See
7. Attach an ohmmeter to the air switch electrical
contacts to check switch action.
NOTE
Use a hand aspirator (Carrier Transicold P/N
07-00177-01), since blowing into tube by
mouth may cause an incorrect reading.
8. With the gauge reading at zero, apply air pres-
sure very slowly to the air switch. An ohmmeter
will indicate continuity when switch actuates.
The switch contacts should close and the ohm-
meter needle move rapidly to 0. Any hesitation
in the ohmmeter indicates a possible problem
with the switch, and it should be replaced.
9. Refer to
for switch setting. If switch
fails to actuate at correct gauge reading, adjust
switch by turning adjusting screw clockwise to
increase setting or counterclockwise to
decrease setting.
10. Repeat checkout procedure until switch actu-
ates at correct gauge reading.
11. After switch is adjusted, place a small amount of
paint or fingernail polish on the adjusting screw
so that vibration will not change switch setting.
8.10 ELECTRICAL SYSTEM COMPONENTS
Procedures for servicing or maintaining the electrical
system components are provided in the following sub-
paragraphs.
8.10.1
Main Microprocessor Module (MM)
For complete Main Microprocessor Module replace-
ment instructions refer to
8.10.2
Power Control Module (PCM)
Figure 8.41 Power Control Module
1. Mounting Fasteners
2. 35 Pin Connector
3. Engine Preheat Terminal (EPH)
4. Plastic Bushings
5. Alternator Positive Terminal (ALT +)
6. Battery Negative Terminal (BAT-)
7. Battery Positive Terminal (BAT +)
8. Door Mounted Legend Sticker
- - - - -
1. Disconnect main power leads at battery.
2. Open Power Control module door. Loosen &
remove stud-post terminal nuts (brass) at termi-
nals BAT+ (7,
); BAT– (6); ALT+ (5)
& EPH (3).
3. Remove nuts holding plastic bushings (4) &
leave hanging on wire.
4. Lift the 4 cable terminals up & off stud-posts.
Remove loose nuts, slide plastic bushings &
cables/terminals out of mounting hole in box.
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