Diagnostics
Important: to ensure smooth operation, all wiring connections in the cab heating system must be secure, clean, and
free from any traces of rust.
Loose connections or oxidation on surfaces will significantly reduce the effectiveness of the heating system.
The heating alternator drive belt must always be correctly tensioned, to ensure that the alternator receives a
steady input horsepower of 4.5HP approx.
Checks must be carried out employing suitable instruments; the use of makeshift contrivances such as indicator lights
with leads and clips is to be avoided, as these can cause serious damage to the system.
TRACING FAULTS IN STANDARD TYPE HEATING SYSTEM (WITH 65 A ALTERNATOR)
Proceed as follows:
1 - With the engine off, switch on the system by turning the potentiometer control to the initial contact, and adjust the
fan speed control.
— Check that warm air emerges from the outlets, and if not, use a voltmeter to test for power at the fan switch. If there
is no voltage reaching the switch, check the wiring and the connections between the switch and the battery, also
the relative fuses located in the fuse box.
2 - With the potentiometer at the initial contact and the fan on (engine off):
A - Check that the brown lead is connected securely to terminal DF of the heater alternator, and the white lead to
terminal D+ of the heater alternator.
B - Test the voltage between contact 7 (fig 3) and contact 12 (fig 3) of the heating system control unit (printed circuit
board T in fig 3).
The voltmeter should read read the following values:
- potentiometer at minimum setting = 0.5 V
- potentiometer rotated half way = 5 V
- potentiometer at maximum setting = 10 V
If the voltmeter readings are correct but the system fails to operate as it should, proceed to run the check of paragraph
3; if the system still fails to operate correctly thereafter, run the check of paragraph 4.
3 - Check that voltage registers at the controls, turn the ignition key to the OFF position and disconnect the black lead
from terminal B+ of the heater alternator, then test the resistance between B+ and B-, which normally should be 1
ohm. If the circuit is found to be open, locate the cause. Reconnect the black lead to terminal B+ when done.
4 - With the potentiometer at the initial contact, test the voltage between contact 6 (fig 3) and contact 10 (fig 3), which
is GND, of the printed circuit board at the heating system control unit (T, fig 3). The voltmeter should read 12V.
If this is not the case, check the wiring connections with the fuse box.
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air conditioning
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