136 EMISSION CONTROLS AND FUEL SYSTEM
Mounting of the AIR control and switching valves
that it is mounted to a bracket on the A/C
compressor.
Thermostatic Air Cleaner
(THERMAC or TAC)
NOTE:
High performance engines
equipped with open-element air cleaners do
not employ this system.
This system is designed to improve drive-
ability and exhaust emissions when the en-
gine is cold. Components added to the basic
air cleaner assembly include a temperature
sensor (connected to a manifold vacuum
source), vacuum diaphragm motor (con-
nected to the temperature sensor), and an in-
let damper door (installed in the air cleaner
inlet snorkel). Additional components of the
system include an exhaust manifold-mounted
heat stove and a hot air duct running from
the heat stove to the underside of the air
cleaner snorkel.
When the engine is cold, the temperature
sensor allows vacuum to pass through to the
vacuum diaphragm motor. The vacuum act-
,-ing on the vacuum motor causes the motor to
close the damper door, which prohibits the
introduction of cold, outside air to the air
cleaner. The intake vacuum then pulls hot air,
generated by the exhaust manifold, through
the hot air duct and into the air cleaner. This
heated air supply helps to more effectively
vaporize the fuel mixture entering the en-
gine. As the engine warms, the temperature
sensor bleeds off vacuum to the vacuum mo-
tor, allowing the damper door to gradually
open.
The usual problems with this system are
leaking vacuum lines (which prevent proper
operation of the sensor and/or motor); torn or
rusted-through hot air ducts and/or rusted-
through heat stoves (either condition will al-
low the introduction of too much cold air to
the air cleaner). Visually check and replace
these items as necessary. Should the system
still fail to operate properly, disconnect the
vacuum line from the vacuum motor and ap-
ply at least 7 in. Hg. of vacuum directly to
the motor from an outside vacuum source;
the damper door should close. If the door does
not close, either the vacuum motor is defec-
tive or the damper door and/or linkage is
binding. If the door closes, but then gradu-
ally opens (with a steady vacuum source), the
vacuum motor is defective.
TIGHTEN TO
10 N-m (88 IN. IBS.)
TIGHTEN TO
10 N-m (88 IN. IBS.)
AIR SWITCHING
VALVE
AIR PUMP
AIR CONTROL VALVE
TIGHTEN TO
3 N ' m ( 2 5 I N . I B S . )
