control rear set temp button is pressed simulta-
neously with the rear control head, then the front
control head press events shall have priority, i.e. if
the front user presses Rear Set Temp down and the
rear user presses Set Temp up, then the rear set
temp will decrease.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - A/C COOL DOWN
TEST
The heater-A/C control module can perform an A/C
cool down test, which is a test performed during the
manufacturing process to confirm that the air condi-
tioning system is performing satisfactorily. This test
can also provide a quick confirmation of air condi-
tioning system performance to the service technician.
If the test is completed satisfactorily, no further ser-
vice is required. If the test is failed, proceed to the
A/C Performance Test to confirm the a/c system is
operating properly, or use a DRBIIItscan tool to
diagnose the A/C system control and distribution sys-
tems. Refer to the appropriate diagnostic informa-
tion.
MANUAL TEMPERATURE CONTROL
The front blower speed and rear blower speed (if
equipped with rear HVAC) must be set to High and
the evaporator temperature sensor must be greater
than 55É F or the test will fail immediately. The test
is activated by depressing the A/C and PWR buttons
simultaneously and holding them depressed for no
less than five seconds. The PWR and A/C LEDs will
blink on and off until the test is complete. If the
LEDs stop blinking before two minutes, then the cool
down test has been completed successfully. If the two
minutes expire without the expansion valve temper-
ature reaching 20É F less than the outside air tem-
perature, then the cool down test has been failed and
further A/C system diagnosis is required. If the test
is failed, the LEDs will continue to blink until the
vehicle has been driven for greater than (8 miles).
AUTOMATIC TEMPERATURE CONTROL
The ambient air temperature in the room where
the vehicle will be tested must be a minimum of 21É
C (70ÉF) for this test. The test is activated by
depressing the A/C and PWR buttons simultaneously
and holding them depressed for no less than four sec-
onds. The snowflake icon and the DELAY text in the
ATC display will blink on and off alternately until
the test is complete. If the snowflake icon and the
DELAY text stop blinking before two minutes, then
the cool down test has been completed successfully. If
the two minutes expire without the evaporator tem-perature reaching 20É F less than the evaporator ini-
tial temperature, then the cool down test has been
failed and further A/C system diagnosis is required.
If the test is failed, the snowflake icon and the
DELAY text will continue to blink across ignition
cycles until the vehicle has been driven for greater
than (8 miles).
DIAGNOSIS AND TESTING - A/C
PERFORMANCE TEST
An air conditioning performance test is the best
way to determine whether the system is performing
up to standard. This test also provides valuable clues
as to the possible cause of trouble with the air con-
ditioning system. The ambient air temperature in the
location where the vehicle will be tested must be a
minimum of 21É C (70ÉF) for this test.
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - WARNING - A/C PLUMBING)
and (Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - FRONT - CAUTION - A/C PLUMBING).
NOTE: When connecting the service equipment
coupling to the line fitting, verify that the valve of
the coupling is fully closed. This will reduce the
amount of effort required to make the connection.
(1) Connect a tachometer to monitor the engine
speed.
(2) Remove the caps from the refrigerant system
service ports and attach a manifold gauge set to
monitor the refrigerant system pressures.
(3) Set the heater-air conditioner controls so that
the compressor is engaged, the air within the vehicle
is being recirculated, the output air is directed
through the panel outlets, the temperature control is
in the full cool position, and the blower motor is oper-
ating at its highest speed.
(4) Start the engine and allow the engine to oper-
ate for about five minutes or until it reaches normal
operating temperature. Then hold the engine speed
at 1000 rpm with the compressor clutch engaged. If
the compressor clutch does not engage, proceed with
diagnosis of the compressor clutch coil. (Refer to 24 -
HEATING & AIR CONDITIONING/CONTROLS -
FRONT/COMPRESSOR CLUTCH COIL - DIAGNO-
SIS AND TESTING).
(5) Close all the vehicle windows and doors.
(6) Insert a thermometer in the left center panel
outlet and operate the engine for five minutes.
RSHEATING & AIR CONDITIONING24-5
HEATING & AIR CONDITIONING (Continued)
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