K 2500 Yukon 4WD V8-6.0L VIN U (2000)
Housing Assembly HVAC: Description and Operation
HVAC System - Automatic
HVAC Air Delivery/Temperature Control Circuit Description
The Electronic Climate Control (ECC) modules (front or rear) serves as an interface between the passenger and the air delivery system. The ECC
modules compares passenger selections with environmental conditions and will adjust air delivery accordingly.
The following air delivery modes are available:
-
Defrost
-
Blend
-
Floor
-
Bi-level
-
Panel
-
External air circulation
-
Internal air circulation
The ECC modules requires two voltage sources in order to operate. Voltage is available at all times through the RADIO fuse.
When the ignition switch is in the RUN position, voltage is available through the HVAC I fuse.
A path to ground for the ECC modules is provided to grounds G200/G410.
The ECC modules receives inputs from the following temperature sensors:
-
The inside air temperature sensor.
A fan located internally to the inside air temperature sensor housing continually draws passenger compartment air over the sensor increasing
accuracy of the temperature reading.
The HVAC I fuse applies voltage for the fan motor when the ignition switch is in the RUN position. A path to ground for the fan motor is provided
to ground G202.
-
The outside air temperature sensor.
-
The sun load temperature sensor.
-
The upper discharge air temperature sensor (front or rear).
-
The lower discharge air temperature sensor (front or rear).
The ECC modules will use the sensor information in order to determine how much airflow to the heater core is required and will adjust the air
temperature valve accordingly. The air temperature valve is located internally to the heater core housing. The position of the air temperature valve is
reported to the ECC modules by the air temperature valve sensor and motor. The HVAC I fuse applies voltage for the air temperature valve sensor and
motor when the ignition switch is in the RUN position.
Operation of the air temperature valve sensor and motor is supported by the following circuits:
-
An 5 volt reference circuit.
-
An ground reference circuit.
-
An signal return path circuit.
-
An motor drive signal circuit.
The ECC modules will control the actuation of individual motors of the HVAC assembly in order to direct air to the appropriate outlets. The HVAC I
fuse applies voltage for the HVAC assembly when the ignition switch is in the RUN position. With voltage available the ECC modules will complete the
current path to ground.
Purge Mode Description
The Electronic Climate Control (ECC) module may access 3 additional purge modes when the following conditions exist:
-
When the system is powered up, purge the system of stale air and/or redirect the air in order to avoid window fogging or other undesirable
conditions.
-
When the ignition is turned ON and the fan increase/decrease knob is not in the OFF position, the ECC module will determine if any of the
undesirable conditions exist.
The ECC module may select from one of the following 3 purge modes in order to eliminate the undesirable condition:
-
The normal purge mode
-
The cold purge mode
-
The A/C purge mode
Normal Purge Mode
Moisture tends to accumulate in the heater and the A/C module assembly after the engine has been turned off. When the engine is restarted and the
A/C system turns ON this moisture may be expelled from the windshield or panel outlets and cause window fogging. The normal purge mode is
bypassed if the fan is in a manual selection.
