A/C Clutch Control Circuit Diagnosis - Isuzu 1999 RODEO Workshop Manual

6E1–56
RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION

A/C CLUTCH CONTROL CIRCUIT DIAGNOSIS

Circuit Description
When air conditioning and blower fan are selected, and if
the system has a sufficient refrigerent charge, a 12–volt
signal is supplied to the A/C request input of the
powertrain control module (PCM). The A/C request signal
may be temporarily cancelled during system operation by
the electronic thermostat in the evaporator case. The
electronic thermostat may intermittently remove the
control circuit ground for the A/C thermostat relay to
prevent the evaporator from forming ice. When the A/C
request signal is received by the PCM, the PCM supplies
a ground from the compressor clutch relay if the engine
operating conditions are within acceptable ranges. With
the A/C compressor relay energized, battery voltage is
supplied to the compressor clutch coil.
The PCM will enable the compressor clutch to engage
whenever A/C has been selected with the engine running,
unless any of the following conditions are present:
f The throttle is greater than 90%.
f The ignition voltage is below 10.5 volts.
f The engine speed is greater than 4500 RPM for 5
seconds or 5400 RPM.
f The engine coolant temperature (ECT) is greater
than 125°C (257°F)
f The intake air temperature (IAT) is less than 5°C
(41°F).
f The power steering pressure switch signals a high
pressure condition position.
Diagnostic Aids
To diagnose an intermittent fault, check for the following
conditions:
f Poor connection at the PCM – Inspect harness
connections for backed–out terminals, improper
mating, broken locks, improperly formed or damaged
terminals, and poor terminal–to–wire connection.
D06RX037