Pontiac Fiero 1988 Service Manual page 26

HEATING AND VENTILATION 1A-1
SECTION 1A
HEATING AND VENTILATION
CONTENTS
G e n e r a l D e s c r i p t i o n
1A-1
D i a g n o s i s — H e a t e r T r o u b l e
1A-2
Insufficient Heating or Defrosting 1A-5
Blower, Electrical 1A-7
Improper Air Delivery/No Mode Shift . . . . . . 1A-8
Too Much Heat 1A-9
Controls 1A-10
Blower Noises 1A-11
O n - V e h i c l e S e r v i c e
1A-13
Heater Module 1A-13
Heater Control Assembly 1A-14
Blower Motor 1A-14
Temperature Cable 1A-14
Heater Core . 1A-14
Lower Heater Outlet 1A-16
GENERAL DESCRIPTION
The base heater system is designed to provide
heating, ventilation and window defrosting.
The power-vent, heat, and defrost provisions of
the base system are controlled within the heater mod-
ule. The module itself is composed of four (4) compo-
nents — a blower case, a heater case, an air inlet and
distribution case, and a heater outlet. Gaskets are used
between the components to prevent air, water and
noise entrance into the passenger compartment.
Air distribution is through a heater outlet,
defroster duct, and power-vent duct work and outlets.
The three modes of the base heater system
(vent, heat, defrost) are controlled by the functional
assemblies within the heater module. These assem-
blies are defined below:
1. Motor & Fan Assembly (Blower)
Provides and regulates air flow from the air inlet
for further processing and/or distribution.
2. Heater Core
Transfers heat from engine coolant to inlet air
thus heating the inlet air.
3. Temperature Valve
Regulates the amount of air passing through the
heater core, thus controlling the temperature and
mix of heated and ambient air.
4. Mode (Defroster, Heater) Valve
Regulates the flow and distribution of processed
air to the distribution (heater or defroster) ducts.
5. Vent Valve
Regulates the flow of non-processed (outside)
air into the passenger compartment.
The operation of these assemblies is controlled
by the levers and switch on the control head. A total
of three (3) indexed snap-in cables are attached to the
module and control levers.
The temperature cable has the slider-type, self-
adjust feature. As the temperature lever of the control
head is cycled through its full range of travel, the
cable clip will assume a position assuring that the
temperature valve will seat in both extreme positions.
The vent and defrost cables also have the self-adjust-
ing feature. Blower speeds (OFF - LO - MED. - HI)
are controllable in all modes (VENT, HEAT,
DEFROST) by the switch on the control head.
1 -FRONT INLET GRILLE
2 - OUTLET
3 - BODY LOCK PILLAR EXHAUST
520104-1A
Figure 1 Interior Body Air Flow & Exit
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 and outboard ends of the instru-
ment panel.