Isuzu 4JA1 Workshop Manual page 483

DTC A/C Compressor System Check
Description
When air conditioning (A/C) and blower fan are
selected, and if the system has a sufficient refrigerant
charge. A 12-volt signal is supplied to the A/C request
input of the Engine Control Module (ECM). The A/C
request signal may be temporarily canceled during
system operation by the electronic thermostat in the
evaporator to prevent the evaporator icing. Also, it is
cancelled when the pressure switch detected abnormal
pressure in the line. When the A/C request signal is
received by the ECM, the ECM supplies a ground from
the A/C compressor relay if the engine operating
conditions are within acceptable ranges. With the A/C
compressor relay energized, voltage is supplied to the
compressor clutch coil. The ECM will enable the
compressor clutch to engage whenever A/C has been
selected with the engine running and enable conditions
are met.
Chart 1 of 2
Step
1 Did you perform the Diagnostic System Check-
Engine Controls?
2 1. Install the scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Turn ON the ignition, with the engine OFF.
4. Monitor the Diagnostic Trouble Code (DTC)
Information of the engine control system with the
scan tool and check whether following DTC(s) is
set:
•
P0115 (Symptom Code 1 & 2)
•
P0645 (Symptom Code 4 & 8)
Are any of the above DTC(s) set?
3 1. Turn ON the ignition, with the engine OFF.
2. Turn ON the blower motor switch.
Does the blower motor turn ON and operate
correctly?
4 1. Turn OFF the blower motor switch.
2. Keep the A/C switch OFF.
Does the A/C Request Signal parameter indicate
OFF?
5 1. Start the engine and let the engine idle.
2. Keep the blower motor switch OFF.
3. Keep the A/C switch OFF.
Does the A/C compressor clutch keep OFF
(disengage)?
6 1. Turn ON the blower motor switch.
2. Keep the A/C switch OFF.
Does the A/C compressor clutch keep OFF
(disengage)?
Action
Engine Control System (4JH1) 6E-229
Condition for Running the A/C Compressor:
• The engine is running.
• The A/C switch is ON.
• The engine coolant temperature (ECT) is less than
105°C(221°F).
A/C Compressor System Check
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views
Value(s) Yes

Go to Step 2

Refer to Applicable
DTC

Go to Step 4

Go to Step 5

Go to Step 6

Go to Step 7
No
Go to Diagnostic
System Check –
Engine Controls
Go to Step 3
Refer to Applicable
Diagnostic Chart in
Heating & Air
Conditioning
Section
Go to Chart 2 of 2
with heater Step 1
OR
Go to Chart 2 of 2
without heater Step
1
Go to Step 11
Go to Chart 2 of 2
with heater Step 7
OR
Go to Chart 2 of 2
without heater Step
4