C.E. Niehoff & Co. C840D Troubleshooting Guides - Manual (Page 4)

Page 4 TG77A
LED COLOR STATUS
TABLE 2 – A2-346 Regulator LED Diagnostics
Alternator and regulator operating normally. GREEN Solid
Low system voltage — Electrical load exceeds
alternator rating at present rotor speed.
ACTION
No action required.
When loads decrease or speed increases, LED
should be solid GREEN. If not, check drive belt
and charging system connections.
Replace alternator. AMBER Solid
High system voltage – May occur during
normal load switching. Indicates voltage above setpoint but below OVCO
threshold (less than 33 volts).
Indicates voltage exceeds 33 V for more than
3 seconds. System diagnosis required. See
OVCO condition in “General Troubleshooting”
section above. RED Solid
Alternator fault — No output. Flashing
Flashing OVCO tripped.
A2-346 Regulator Troubleshooting
Main diagnostic feature of these regulators is a tricol-
ored LED opposite the alternator-regulator harness
receptacle. LED works like a voltmeter, measuring
charging voltage. See Table 2 for LED diagnostics.
These regulators have OVCO (overvoltage cutout) that
will trip at vehicle electrical system voltage above 33
volts that exists longer than 3 seconds. OVCO feature
detects high voltage and reacts by signaling relay in
alternator field circuit to open. This turns off alternator
(LED is flashing RED). OVCO circuit can also optionally
reset when system voltage normalizes after 2-minute
wait.
An additional A9-4036 harness may or may not be used
with the A2-346 regulator:
• When A9-4036 temperature/voltage sense harness is
not connected, regulator will operate in fixed voltage
setting determined by the select switch position on
the bottom of the regulator.
• When A9-4036 temperature/voltage sense harness is
connected, regulator will automatically optimize the
charge voltage for battery type selected based on
temperature. Also, vehicle manufacturer-requested
functions of 1939 interface are available through
connector.
General Troubleshooting
OVCO condition
Shut down vehicle and restart engine. If alternator func-
tions normally after restart, a “no output condition” was
normal response of voltage regulator to “high voltage”
condition. Inspect condition of electrical system, includ-
ing loose battery cables, both positive and negative. If
battery disconnects from system, it could cause “high
voltage” condition in electrical system, causing OVCO
circuit to trip.
If you have reset alternator once, and electrical system
returns to normal charge voltage condition, there may
have been a one time, high voltage spike, causing OVCO
circuit to trip.
If OVCO circuit repeats cutout a second time in short
succession and shuts off alternator field circuit, try
third restart. If OVCO circuit repeats cutout, check that
pin F in alternator-to-regulator harness is not shorted to
B+ terminal on alternator. If it is shorted, alternator is
defective. If not, regulator is defective.
No air-conditioning/NO ALT OUTPUT light is on
Some older vehicles may experience a condition when
the air-conditioning may drop out during normal
vehicle operation. If that should occur, check for regula-
tor setpoint voltage at D+ terminal and 12 V-18 V at P
terminal. If present, check vehicle wiring. If not present,
check for diode voltage drop between pin E on alterna-
tor-to-regulator harness and alternator B+ terminal. If
not present, alternator is defective. If present, substitute
a known good regulator, run engine, and check for regu-
lator setpoint voltage. If present, original regulator was
defective. If not present, go to troubleshooting chart on
page 5.
Section C: On-Vehicle Troubleshooting