Air Conditioning (A/C) Controls - Ecm Inputs (2.5L Diesel) - Jeep Cherokee 2000 Service Manual

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DESCRIPTION AND OPERATION (Continued)
Fig. 5 Engine Coolant Temperature Sensor Location
1 – PCM ENGINE COOLANT TEMPERATURE (ECT) SENSOR
2 – ECM ENGINE COOLANT TEMPERATURE (ECT) SENSOR
3 – ECM ECT SENSOR HARNESS CONNECTOR
4 – PCM ECT SENSOR HARNESS CONNECTOR
Fig. 6 Engine Speed Sensor Location
1 – ENGINE SPEED SENSOR
2 – GROMMET
3 – MOUNTING BOLT(S)
4 – LEFT REAR OF ENGINE
5 – TRANSMISSION
The flywheel has four notches at its outer edge
(Fig. 7). Each notch is spaced equally every 90°. The
notches cause a pulse to be generated when they
pass under the speed sensor (Fig. 7). These pulses
are the input to the ECM. The input from this sensor
determines crankshaft position (in degrees) by moni-
toring the notches.
The sensor also generates an rpm signal to the
ECM. This signal is used as an input for the control
FUEL SYSTEM—2.5L DIESEL ENGINE
Fig. 7 Speed Sensor Operation
1 – ENGINE SPEED SENSOR
2 – FLYWHEEL
3 – NOTCHES
of the generator field, vehicle speed control, and
instrument panel mounted tachometer.
If the engine speed sensor should fail, the system
is unable to compensate for the problem and the car
will stop.
AIR CONDITIONING (A/C) CONTROLS—ECM
INPUTS
DESCRIPTION
The A/C control system information applies to fac-
tory installed air conditioning units.
A/C REQUEST SIGNAL: When either the A/C or
Defrost mode has been selected and the A/C low and
high–pressure switches are closed, an input signal is
sent to the ECM. The ECM uses this input to cycle
the A/C compressor through the A/C relay.
If the A/C low or high–pressure switch opens, the
ECM will not receive an A/C request signal. The
PCM will then remove the ground from the A/C relay.
This will deactivate the A/C compressor clutch. Also,
if the engine coolant reaches a temperature outside
normal of its normal range, or it overheats, the ECM
will deactivate the A/C clutch.
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