1988 PONTIAC FIERO Service Repair Manual

1A-2 HEATING AND VENTILATION
520003-1 A
Fig. 3 Interior Body Air & Exit - Typical Sedan, Station Wagon
self-adjusting feature. Blower speeds are controllable in
all modes (VENT, HEAT, DEFROST) by the switch
on the control head.
The power-vent ventilation feature is available in
the vent mode. Outside air enters the plenum and is
driven by the blower to the temperature valve. In the
cold position of the temperature valve, air bypasses the
heater core to the vent valve opening and enters the
passenger compartment through the vent duct and
outlets
in the center of the instrument panel. If some
heated air is desired, the temperature valve may be
opened. This allows mixed (tempered) air to flow out
the center vent opening. Blending air between modes
can be done by varying the mode selector.
Varying the selector between "Heat" and
"Defrost" will allow more air or less air to be directed
out either the defroster outlet or the heater outlet. The
closer the mode selector is positioned to the "Heater"
position, the larger the amount of air coming out the
heater outlet. The closer the mode selector is
positioned to "Defrost," the larger the amount of air
going to the windshield. The temperature of this air is
governed by the temperature lever position. Side window
defogging, if so equipped, is
provided via ducts in the outboard corners of the
instrument panel. Maximum air flow from these vents
will be in "Heater" mode with reduced air flow in
"Defrost" mode.
Varying the mode selector between "Heater" and
"Vent" positions varies the proportion of air coming
out the heater outlet and the center vent outlets. With
the selector in some midway position, air coming out
the center vent outlets will be ambient temperature,
while air out the heater outlet will be mixed warm air,
its temperature depending on temperature lever
position.
In the heat and defrost mode, outside air is driven by
the blower to the temperature valve which, depending
upon its position as controlled by the operator, distributes
all or some portion of the inlet air through the heater core.
The vent valve will prevent air entry into the vent duct and
direct this ambient air to the mix portion of the heater
module. The air is thus heated, mixed, and then directed
into either the defroster duct or the heater outlet by the
position of the mode valve and control lever.
A small
amount of air is bled to the side window defogger system.

HEAPING AND VENTILA"T0N 1A-3
1, LEFT AND RIGHT SIDE WINDOW 3. POWER VENTIHEAT 5. LEFT AND RIGHT RAM AIR
DEFOG OUTLETS* OUTLETS VENT OUTLETS*
2. LEFT AND RIGHT DEFROSTER 4. RAM AIR VENT
OUTLETS CONTROLS* * NOT ON ALL MODELS J10001-1A-F
Fig. 4 Heater Ventilation System - Typical
1-THIS POSITION ALLOWS OUTSIDE AIR FLOW 3-THIS
POSITION ALLOWS ABOUT 80% AIR
TO FLOOR OUTLET. (ADDITIONAL VENTED FLOW
TO WINDSHIELD AND 20% TO FLOOR.
AIR CAN BE DISTRIBUTED INSIDE CAR BY
OPERATING VENT KNOBS.) 4-TEMPERATURE
LEVER POSITION WILL
REGULATE OUTLET AIR TEMPERATURE BY
2-POSITION OF
THIS SYSTEM SELECTOR BLENDING
THE INCOMING OUTSIDE AIR
LEVER DETERMINES AIR FLOW FROM THROUGHIAROUND THE HEATER CORE.
FLOOR, INSTRUMENT PANEL OR WIND-
SHIELD OUTLET - IN "HEATER", FLOW IS 5-THE
FAN CONTROL LEVER (OFF - HI) PRO.
ABOUT
80% TO FLOOR AND 20% TO WIND- VIBES SPEED CONTROL OF THE FAN.
SHIELD OUTLETS (AND
SlDE WINDOW DE-
FOGGERS).
Fig. 5 Heater Control - Typical

1A-4 HEATING AND VENTILATION
1-DEFROSTER OUTLET
7-PURGE DOOR OPENS TO ALLOW
11-AIR DOOR CLOSES OFF HEATER
AIR FLOW INTO CAR UNDER I.P.
AND DEFROSTER OUTLETS WHEN
2-BLENDED AIR WHEN SYSTEM SELECTOR LEVER SYSTEM SELECTOR LEVER IS
IS MOVED TO "OFF"
MOVED TO "OFF"
3-HEATER CORE
8-UNTEMPERED AIR
12-DEFROSTER DOOR MOVES BY
4-BLOWER OPERATION OF HEATER
9-WARMED AIR CONTROLS SYSTEM SELECTOR
5-DASH PANEL LEVER
10-TEMPERATURE DOOR MOVES BY
6-OUTSIDE AIR FROM COWL
OPERATION OF TEMPERATURE "ON
SOME MODELS ALSO
PLENUM CHAMBER
LEVER ON HEATER CONTROL SUPPLIES
SIDE WINDOW
DEFOGGING DUCTS.
. -.
Fig. 6 Typical Heater System Air Flow

HEATING AND VENTILATION 1A-5
@ INSUFFICIENT HEATING OR DEFROST lNG
OF THE HEATER
IF PROBLEM
NOT RESOLVED THEN
HECK FOR AIRFLOW OUT DEFROSTER
VENT OUTLETS
INSTALL THE RADIATOR CAP. WITH ENGINE WARM,
DRIVE THE VEHICLE AT
48 KPH(3OMPH). WITH A THER-
MOMETER, CHECK THE AMBIENT AIR TEMPERATURE
CONTINUED AT TOP OF NEXT PAGE
Fig. 7 Insufficient Heating or Defrosting Diagnosis Procedure (7 of 2)

1A-6 HEATING AND VENTILATION
CHECK VEHICLE FOR
COLD AIR LEAKS AT DASH,
HEATER CASES AND FROM
VENTS. CHECK
UNDERSEAT FOR
OBSTRUCTIONS.
w
TEN FOR DOOR SLAM PRIOR TO THE END
CHECK THE TEMPERA-
TURE DOOR ADJUSTMENT,
CABLES, LINKAGE AND AD-
JUST TO FULL HOT. CHECK
I
WITH THE TEMPERATURE
DOOR FULL HOT, START THE
VEHICLE. CHECK THE TEMPER- ATURE OF THE HEATER INLET
AND OUTLET HOSES BY FEEL.
THE AIR TEMPERATURE
AROUND THE HOSES MUST BE AT LEAST
85OF.
I
WITH THE BLOWER ON
HIGH, MOVE THE TEMP-
ERATURE LEVER FROM
FULL HOT TO FULL
COLD AND LISTEN FOR
AIRFLOW CHANGE.
CHECK THE TEMPER-
ATURE DOOR AD-
JUSTMENT, CABLES,
CONTROL, LINKAGE
&
BETWEEN THE
COOLANT REPLACE.
Fig. 8 Insufficient Heating or Defrosting Diagnosis Procedure (2 of 2)

HEATING AND VENTILATION 1A-7
@ BLOWER ELECTRICAL
LOCATE SHORT IN THE
FOLLOWING WIRES:
1. FROM THE FUSE PANEL
2. FROM THE BLOWER
SPEED SWITCH TO THE
HEATER RESISTOR BLOCK.
3. FROM THE HEATER RE-
SISTOR BLOCK. CONNECT A
JUMPER LEAD FROM THE BAT-
TERY POSITIVE TERMINAL TO
ANY
WlRE TERMINAL IN THE
CONNECTOR. USE
12 VOLT
TEST LIGHT TO CHECK FOR
VOLTAGE AT THE CORRES-
PONDING WIRE ON THE
USE THE
12 VOLT
TEST LIGHT TO
CHECK THE POWER
FEED TERMINAL ON
THE BLOWER
SPEED SWITCH
TEST LAMP DOES BLOWER
SPEED SWITCH.
REPAIR OPEN IN FEED
WlRE FROM RESISTOR TO
BLOWER MOTOR.
Fig. 9 Blower Electrical Diagnosis

1 A-8 HEATIN,G AND VENVILAVIBN
@ IMPROPER AIR DELIVERY OR NO MODE SHlFT
WITH THE VEHICLE ON AND THE ENGINE WARM, RUN THE FOLLOWING FUNC-
I TIONAL CHECKS. CHECK CABLES FOR EXCESSIVE EFFORT OR BINDING.
POWER VENT
OUTLET HEATER
OUTLET DEFR.
OUTLET
MODE
SIDE
WINDOW
DEFOGGER
OUTLET
VENT NO
AIRFLOW NO
AIRFLOW NO
AIRFLOW AIRFLOW
No I I I
COLD HIGH HIGH VENT AMBIENT
AIRFLOW NO
AIRFLOW NO
AIRFLOW AIRFLOW
No I
HEATER
DEFROSTER COLD HIGH HIGH
TO HOT
COLD
HIGH HIGH
TO HOT NO
AIRFLOW COLD
TO
HOT
AIRFLOW
MINIMUM COLD TO
HOT
AIRFLOW MINIMUM
COLDTO HOT
AIRFLOW
COLD TO
HOT
AIRFLOW MINIMUM
COLD TO HOT
AIRFLOW
MINIMUM COLD TO
AIRFLOW
N 0
AIRFLOW
CONNECTED
& CABLE SHEATH RETAINED
G20025.1A
Fig. 10 Improper Air Delivery Or No Mode Shift Diagnosis

HEATING AND VENTILATION 1A-9
@TOO MUCH HEAT
TEMPERATURE LEVER
TO CONTROL END OF
LOW THE ENGINE
PERATURE DOOR TO WARM UP. WITH
TEMPERATURE HEATER
DEFROST- ER & VENT DOOR
BLOWER INLET & REPAIR
Fig.
11 Too Much Heat Diagnosis.