On-Car Procedure - Pontiac FIREBIRD 1972 Service Manual

1B-2 1972 PONTIAC SERVICE MANUAL
The voltmeter on the tester panel has a range of 0 to 15
volts D.C. The voltage monitored by the meter is con-
trolled by the knob just below the meter at all times except
when the Temperature Dial Calibration switch is in the
"CAL." (calibrate) position. The "#2 Programmer" po-
sition allows the tester to directly monitor the input volt-
age to the programmer. The "#6 Blower" position allows
the tester to directly monitor the voltage applied to the
blower motor. The "#7 LO-Relay" position indicates that
the Lo-relay has energized and that the relay contacts
have closed if battery voltage is read on the meter. The
"#8 Auto-Relay" position indicates that the auto-relay
has energized and that the relay contacts have closed if
battery voltage is read on the meter. The "Probe and Clip"
position connects the probe and clip in the tester's storage
compartment directly to the voltmeter. This makes it
possible to use the voltmeter to check various other volt-
ages in the ATC system. The red probe should always be
connected to positive and the alligator clip lead should
always be connected to the more negative terminal.
When the Manual-Automatic switch is in the AUTO-
MATIC position and the Temperature Dial Calibration
switch is OFF, the tester monitors voltages on the voltme-
ter according to the voltage knob position. When the
Manual-Automatic switch is in the MANUAL position,
the temperature dial on the control panel, the ambient
sensor and the in-car sensor are disabled and the Manual
Control knob replaces them. The numbers around the
Manual Control knob represent the resistance in ohms
that is replacing the resistance of the temperature dial, the
ambient sensor and the in-car sensor. If the knob is rotated
to the MAX. COLD position, the programmer should
move to the full A/C position. If the knob is rotated to the
MAX. HEAT position, the programmer should move to
the maximum heat position. The Manual Control knob is
operational when the Manual-Automatic switch is in the
MANUAL position.
When the Temperature Dial Calibration switch is in the
"CAL." position, the voltmeter monitors the voltage di-
rectly across the temperature dial on the control head.
When the "COMPARE" button is pressed, the voltmeter
reads the voltage across a precision resistor in the tester.
By moving the temperature dial on the control panel, the
two voltage readings can be made the same. After this is
accomplished, the temperature dial on the control head
should read the correct temperature as indicated on the
tester panel. If it does not, the temperature dial clutch
should be held and the dial slipped to read the correct
temperature (see Temperature Dial Calibration Proce-
dure).
The Temperature Dial Calibration switch should always
be in the OFF position unless the temperature dial on the
control head is being calibrated.
DIAGNOSTIC PROCEDURE
Diagnosis of a malfunction in the system can be simplified
by a logical, systematic procedure which can minimize
diagnosis time and effort. Lack of a logical, systematic
procedure could complicate diagnosis of a relatively mi-
nor malfunction or waste time and effort attempting to
diagnose a malfunction which does not actually exist.
To simplify diagnosis of the ATC system, the following
procedure should always be employed:
A. UNDERSTAND SYSTEM OPERATION.
Before a malfunction in the ATC system can be diagnosed
and corrected, an understanding of how the system oper-
ates under normal conditions is essential. System operat-
ion is described in GENERAL DESCRIPTION and B
SERIES DESCRIPTION.
B. OBSERVE SYSTEM OPERATION.
The most important part of diagnosing a problem is to
determine exactly what the complaint is and whether this
complaint actually stems from a malfunction in the sys-
tem. (Without a thorough understanding of how the sys-
tem is supposed to operate, a complaint stemming from
misunderstanding of system operation or improper setting
of the control panel lever could result in the search for a
malfunction that does not exist.) If complaint is of a condi-
tion that occurs only periodically (intermittent), the mal-
function should be observed before diagnosis and repair
are attempted.
C. ISOLATE THE MALFUNCTION.
The main objective when troubleshooting the ATC system
is to isolate the malfunction to either the control head
(control panel), the sensor string, the ATC vacuum system
on the car, the car electrical system or the programmer.
To isolate the malfunction refer to ON CAR PROCE-
DURE. After this preliminary isolation is completed, the
actual malfunction can then be diagnosed quickly.
ON CAR PROCEDURE
Do not skip any steps in the Troubleshooting Procedure
unless instructed to do so.
Start car and place control head selector lever in the
AUTO position and the temperature dial at 75". Al-
low enough time for the car engine to warm up and
the ATC system to come on if the system were acting
normally. If the system does not come on, skip to
Step 3.
After the system has turned on, rotate the tempera-
ture dial slowly back and forth looking for abnormal
operation of the system. Then move the selector lever
to each of the various positions and look for any
malfunction in system operation. By observing a mal-
function and noting when it occurs, it is often possible
to isolate the problem to a certain area of the system.