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HEATING & A/C
*REAR BOOSTER FAN RUNS AT ONLY ONE SPEED —
TEST
3
Turn the ignition off.
Reconnect all previously disconnected components.
Connect the DRBIII X10 Scope Probe CH7061 to the DRBIII .
Select the following from the DRBIII menu: PEP Module Tools; Lab Scope; Live
Data; and Lab Scope.
Set the time to 10ms/Div.
Set the voltage range to +20.0v.
Set the offset to 4.00v.
Set the Probe to X10.
Start the engine.
Press the ATC's PWR switch on.
Press the REAR fan mode switch on, so that it is in manual mode. The word REAR
should display on the ATC display panel. The word AUTO should not be displayed.
Using the X10 Scope Probe, back probe the Rear Booster Fan Control circuit in the
ATC C1 harness connector.
NOTE: The RR Booster Fan Power Module provides a 12.0v signal to the ATC
over the Rear Booster Fan Control circuit. The ATC provides a variable duty
cycle ground to the 12.0v signal based on input from the Rear Booster Fan
Rear Control switch.
NOTE: When the fan speed is set to low, the ATC provides a short duty cycle
(less time grounding the signal voltage).
NOTE: As higher fan speeds are requested, the ATC increases the duty cycle
(more time grounding the signal voltage).
NOTE: When the highest fan speed is requested, the duty cycle increases to
where the signal pattern is almost a flat line (with brief voltage spikes).
Set the fan speed to low, then slowly raise the fan speed to high while observing the
DRBIII display.
The voltage on the scope patten should cycle from approximately 0 volts (duty cycle
on) to 12.0 volts (duty cycle off) for all fan speeds.
The duty cycle pattern should change smoothly as the fan speed changes from low to
high.
Does the DRBIII display the voltage range and duty cycle as described above?
Yes → Replace the Rear Booster Fan Power Module in accordance with
→ Replace the Automatic Temperature Control (ATC) in accordance
No
ACTION
the Service Information.
Perform BODY VERIFICATION TEST - VER 1.
with the Service Information.
Perform BODY VERIFICATION TEST - VER 1.
578
Continued
APPLICABILITY
All
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