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HEATER COMPONENTS
NOTE: Figures 4-3 and 4-4 illustrate both the heater
system and air conditioning system parts contained in
the cab mounted enclosure. Refer to Section "M" for
additional information regarding air conditioning sys-
tem components, maintenance and repair.
CIRCUIT BREAKERS
Before attempting to troubleshoot the electrical circuit
in the heater enclosure, turn key switch ON and verify
circuit breaker CB31 (located on Power Distribution
Module behind operator's seat) and the internal heater
circuit breaker have not opened by verifying + 24VDC
is present on the junction block (24, Figure 4-4).
HEATER CONTROL COMPONENTS
When the operator adjusts the selection control knob
(6, Figure 4-2), a signal is sent to the Heater Control
Module (2, Figure 4-3). If the operator requests a cooler
temperature in the cab (by turning the control counter-
clockwise) the Heater Control Module will close the
water control valve (3) to block coolant flow through
the heater coil (8). Turning the knob fully clockwise will
open the valve to allow maximum flow.
N04020
Test
Verify the motor on the water control valve operates
when the control (6, Figure 4-2) is rotated throughout
the red area. If the motor fails to operate, the heater
control module may be defective.
A mechanical defect in the water control valve (3,
Figure 4-3) may allow heated water to pass through the
hose between the valve and the heater core when in
the off position. Verify the motor in the valve operates
properly throughout its range from full off to full on. If
the hose is warm and the heater selector switch is in
the off position, internal leakage may be present. Also,
if the heater core fails to deliver warm air when the
engine is at normal operating temperature, the valve
may not be opening properly.
HEATER COIL
The heater coil receives engine coolant through the
Water Control Valve when HEAT is selected. If the
selection control is placed in between the red and blue
area, or turned counterclockwise to the blue area,
coolant flow should be blocked.
If the heater control module and water valve appear to
be working properly, yet no heat is apparent in the
heater coil, the coil may be restricted. Remove and
clean or replace the coil.
FIGURE 4-3. CAB HEATER COMPONENTS
Operator Comfort
1. Heater Enclosure
2. Heater Control Module
3. Water Control Valve
4. A/C Refrigerant Hoses
5. Water Outlet (to Engine)
6. Water Inlet (from Engine Water Pump)
7. Evaporator Coil
8. Heater Coil
N4-3
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Table of Contents
Troubleshooting
