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10-6
Chapter 10
– Component Repair or Replacement
Go to Chapter Start-
Table of Contents-
IndexFan Clutch Will Not Activate.
1.
Check power supply to terminals #3 and #4 with voltmeter
or trouble light. System pressure must be above 230 PSIG
(restrict air flow through the condenser if necessary to
achieve this pressure). Check opposite terminals for switch
function. If switch does not close and activate the fan
clutch, replace the Trinary™.
Note:
Some air-clutching engine-fan systems use normally
closed Trinary™ switches (Bendix, Horton, etc.).
When the operating pressure is reached, the fan cir-
cuit will open and the fan will come on.
2.
Faulty solenoid (air-clutching fans) or wiring. If the Tri-
nary™ switch functions in the above test, check wiring to
solenoid valve, fan, or relay, and determine if the valve or
relay is functioning properly.
Air Operated Controls
Air controls have become important in truck HVAC system operation. In
discussing troubleshooting, we will cover the module air control system.
The four major components of this system are illustrated in Figure 10-2
and described as follows:
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PINTLE ASSEMBLY
O-RINGS
OPEN
AIR
AIR
AIR BLOCK CLOSED
AIR BLOCK OPEN
CONTROL LEVER
WITH DEPRESSIONS
CLOSED
Air Block—
A molded plastic or machined metal block with air
passageways; inlet, outlet and vent ports.
Pintle—
A valve stem with head and O-ring seal
Figure 10-2
The AIR BLOCK is shown
and described in this illus-
tration.