Dodge RAM TRUCK 1500 1995 Service Manual page 1173

COMPONENT DESCRIPTION/SYSTEM OPERATION—DIESEL ENGINE 14 - 9 1
B R
UPPER PART OF
INTAKE MANIFOLD J9414-105
Fig. 5 Air Heater Location
CABLE
MOUNTING
STUDS
J95U-76
Fig. 6 Heater Elements—Typical
Two heavy-duty cables (Fig. 5) connect the 2 air
heater elements to the 2 air heater relays. Each of
these cables will supply approximately 95 amps at 12
volts to an individual heating element within the
heater block assembly (Fig. 6).
Electrical supply for the 2 air heater elements is
controlled by the powertrain control module (PCM)
through the 2 air heater relays. Refer to the follow­
ing Intake Manifold Air Heater Relays for more in­
formation.
INTAKE MANIFOLD AIR HEATER RELAYS—PCM
PINS # 1 5 AND #16—PCM OUTPUT
The 2 relays are located in the engine compartment
below the left battery (Fig. 7).
BATTERY
(LEFT SIDE)
Fig. 7 Intake Manifold Air Heater Relays
The powertrain control module (PCM) operates the
2 heating elements within the air heater assembly
through the 2 intake manifold air heater relays. The
air heater elements are used to heat incoming air
flowing into the intake manifold. This will help en­
gine starting and improve driveability with cool or
cold outside temperatures.
The relays may be energized by the PCM before
and after cranking. This will depend on inputs the
PCM receives from: the intake manifold air tempera­
ture sensor, the engine speed sensor and the vehicle
speed sensor.
With a cool or cold engine, the air heater relays
and the air heater elements may be activated for a
maximum time of approximately 3 1/2 minutes. Refer
to the following Air Heater Cycle Chart for a temper­
ature/time comparison of relay engagement.
In this chart, Pre-Heat and Post-Heat times are
mentioned. Pre-heat is the amount of time the relay
circuits are activated when the ignition (key) switch
is ON, but the engine has yet to be started. Post-heat
is the amount of time the relay circuits are activated
after the engine is operating.