TEMPERATURE REFERENCE TABLE
Ambient Temp. Minimum
Floor
Outlet
Temp.
Celsius Fahrenheit Celsius Fahrenheit
15.5° 60° 62.2° 144°
21.1° 70° 63.8° 147°
26.6° 80° 65.5° 150°
32.2° 90° 67.2° 153°
If the floor outlet air temperature is insufficient,
refer to Cooling for specifications(Refer to 7 - COOL-
ING - DIAGNOSIS AND TESTING). Both heater
hoses should be HOT to the touch (coolant return
hose should be slightly cooler than the supply hose).
If coolant return hose is much cooler than the supply
hose, locate and repair engine coolant flow obstruc-
tion in heater system.
POSSIBLE LOCATIONS OR CAUSE OF
OBSTRUCTED COOLANT FLOW
(1) Pinched or kinked heater hoses.
(2) Improper heater hose routing.
(3) Plugged heater hoses or supply and return
ports at cooling system connections, refer to Cooling.
(4) Plugged heater core.
(5) Air locked heater core.
(6) If coolant flow is verified and outlet tempera-
ture is insufficient, a mechanical problem may exist.
POSSIBLE LOCATION OR CAUSE OF INSUFFICIENT
HEAT
(1) Obstructed cowl air intake.
(2) Obstructed heater system outlets.
(3) Blend door not functioning properly.
TEMPERATURE CONTROL
If temperature cannot be adjusted with the TEMP
knob/button on the control panel, the following could
require service:
(1) Blend door binding.
(2) Faulty blend door actuator.
(3) Improper engine coolant temperature.
(4) Faulty A/C Heater Control. (Refer to Appropri-
ate Diagnostic Information)
DIAGNOSIS AND TESTING - SELF
DIAGNOSTICS
DIAGNOSTIC TROUBLE CODES (DTC’s)
Both the Automatic Temperature Control (ATC)
and the Manual Temperature Control (MTC) systems
are controlled by the Body Control Module (BCM).
Both systems can be diagnosed by the DRBIIIt scan
tool or the vehicles own control head display. Refer to
the DRBIIIt menu for checking Diagnostic Trouble
Codes (DTC’s). Note that there are three DTC tables.
The ATC and MTC DTC table contain faults that are
common to both the ATC and the MTC system. The
same diagnosis can be used for both systems. The
DTC’s cover operation of the climate control unit
actuators, doors, evaporator temperature sensor,
ambient temperature sensor and the A/C refrigerant
system. The MTC DTC table covers Fault Codes that
are for the MTC Control Head and wiring and are
not used on an ATC system. The ATC DTC table has
DTC’s for ATC Head Communications, In-Car Tem-
perature Sensor and Sun Sensor which are not in a
MTC system.
Some conditions of low battery voltage or
extremely cold weather can generate a DTC for the
climate control system actuators, evaporator probe,
in-car temperature sensor (ATC), or ambient temper-
ature sensor, even in a properly operating system. It
is recommended that all the DTC’s be checked as fol-
lows to assure a part is faulty.
Climate Control Sensor DTC Check
(1) Clear the DTC.
(2) Operate the HVAC system with the engine run-
ning for a minimum of 30 seconds.
(3) Check for DTC’s.
(4) Perform diagnostics if the DTC appears again.
(Refer to Appropriate Diagnostic Information)
Climate Control Actuator Check.
(1) Clear the DTC.
(2) Perform HVAC system calibration. (Refer to 24
- HEATING & AIR CONDITIONING - STANDARD
PROCEDURE - HVAC SYSTEM CALIBRATION)
(3) Perform diagnostics if the DTC appears again.
(Refer to Appropriate Diagnostic Information)
If a DTC does not appear when using the proce-
dures above, check the history of the vehicle for a low
battery condition, or ambient temperatures below
40°F. Removing connections without disconnecting
the battery may also generate a DTC on a good part.
The battery should always be disconnected when ser-
vicing electrical parts.
LH HEATING & AIR CONDITIONING 24 - 3
HEATING & AIR CONDITIONING (Continued)
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