Question about 1999 Chevrolet Suburban
I have a 1995 Suburban with A/C and rear defog. The HVAC system stays at its default floor mode and will not go to defrost or vent. The flap under the driver dash is not stuck. In addition the light ups for recirc. and A/C on the dash unit do not come on. Could it be the A/C control module. I guess there is a fault internally in the control module that causes the A/C and recirc. to not light up when engaged. Any other ideas?
I have a 1500 chevy picup that did the same thing the control panel (blower, temp, and selector) is what was the problem with mine replaced that and fixed it. Very easy to chg.front of dash pops off control panel pops out 1 plug ( yours may have 2 plugs)
pop back in and your done.
Posted on May 28, 2009
I have a 99 GMC Suburban SLT, my defrost stopped working just had heat on floor only. There is a floor control module that hooks to the flap control arm, it was locked up. Easily seen, by the drivers side floor blower. There were only 2 bolts holding it on, take it off and see if you can disengage it by hand, if not that will be your problem. Mine was $40 with me installing it. GOOD LUCK!
Posted on Nov 30, 2011
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Posted on Jan 02, 2017
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The mode and defrost actuators are connected to the mode and defrost doors by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If the HVAC control module detects a fault with the mode or defrost doors the HVAC control module will try to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode and defrost door actuators. When the mode switch is placed in the defrost or defog positions the A/C is commanded on and the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all modes and recirculation is only available in the panel and bi-level modes.
Circuit Description The following DTCs are for the HVAC door actuators: ?€¢
B0248 is for the defrost actuator.
B0263 is for the mode actuator.
B0408 is for the left air temperature actuator.
B0418 is for the right air temperature actuator.
The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The logic circuit inside the actuators receives control signals from the HVAC control module and controls the internal stepper motor. When a door positional change is required, the HVAC control module calculates a commanded door position. The module compares the commanded door position to the actual door position and determines the needed direction of motor rotation. The module applies a signal voltage to the door control circuit that is an input to the internal logic circuit of the door actuator. A 5 volt signal increases the door position. A 0 volt signal decreases the door position. When the commanded door position is equal to the actual door position, the HVAC control module sends a 2.5 volt signal to the door actuator and motor rotation stops. The ignition 3 voltage circuit provides source voltage to the logic circuit. The module provides ground to the actuator logic circuit through the low reference circuit. I would start by having the HVAC control module checked for DTC'S -diagnostic trouble codes First . Then check the system by using scan tool data . 1
Did you perform the HVAC Diagnostic System Check?
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Your probably better off taking this to a ASE certified repair facility ! You probably have bad Heater / A/C control panel . HVAC Control Module Malfunction
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