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Chapter 7
– Inspection & Maintenance
7-6
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Table of Contents-
IndexB. Turn the AC System On
– This will power the thermostat and
clutch. If it does not come on, use the AC mode switch to check the
leads to the switch. You should be able to hear a “click” from the
thermostat and hear the clutch drive plate “snap” against the clutch
pulley. You can not check thermostat cycling on and off until you do
the performance inspection. Figure 7-5 illustrates a typical AC elec-
trical system and the places you should inspect.
TRINARY™
SWITCH
RECEIVER-
DRiER
RELAY
CONDENSER
MOTOR
BLOWER/
MOTOR
ASSEMBLY
ROTARY
SWITCH
THERMOSTAT
EVAPORATOR
TXV
CONDENSER
FAN MOTOR
IGNITION
30 AMP
FUSED
CIRCUIT
COMPRESSOR
CLUTCH
POWER IN
RESISTOR
C. Check Fuses
– If there is a failure and you have made sure all
connections are clean and tight, you need to check fuses—in-cab as
well as in-line.
D. Check Clutch Engagement
– Since you can’t see and may not
hear the clutch engage, get out and look at the clutch. If it’s engaged,
you will see that the drive plate is against the pulley and not slightly
spaced from it. If you are not sure the clutch is engaged, look for the
lead wire connector near the clutch. Break and close that connection.
The clutch will disengage and engage again.
E. Test Blower Speed Operation
– Some systems have a common
switch that turns on the air conditioner and powers the blower
motor. Test blower speed operation by adjusting this or the separate
blower control switch. Feeling the air flow from the ducts or note
blower sound (speed) changes.
F. Inspect Roof Mounted Condensers
– Don’t forget to inspect
roof mounted condensers andAC systems for dirt and debris. Be sure
the condenser fan(s) are working properly and all parts and electri-
cal connections are securely fastened. The roof mounted condenser
fans may come on when the system is turned on. Like the thermostat
and most clutches, the normal on-off cycling action can not be
observed until the engine is running with the AC system on.
Figure 7-5
The electrical system in-
spection points are noted
with check marks (
4
) on
this wiring diagram (electri-
cal schematic).