Question about 1999 Chevrolet Suburban

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1995 Suburban HVAC - no defrost or vent only floor mode

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?

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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

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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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1 Answer

My heater is stuck on the windshield and floor what actuator needs to be changed


Air Distribution
The HVAC control module controls the distribution of air by the use of a defrost actuator and a mode actuator. The modes that may be selected are:
?€¢
Defrost


?€¢
Defog


?€¢
Panel


?€¢
Bi-Level


?€¢
Floor

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?
Go to Step 2
Go to Diagnostic System Check - HVAC Systems - Manual

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the appropriate HVAC door actuator ON and OFF while observing the corresponding Door Actual parameter.
Does the scan tool indicate that the value of the appropriate Door Actual parameter changes?
Go to Diagnostic Aids
Go to Step 3

I would

Apr 02, 2016 | 2003 Chevrolet TrailBlazer

1 Answer

2005 Ford Focus. Air is blowing out of the floor vents and defrost vents but not dash vents. Also the knob will not go onto the dash vent option it's like it just springs back up.


A failure has occurred in the HVAC system, legally, when a fault happens the hvac system will default to defrost/floor. Further diagnostics will be needed to determine issue.

Jun 05, 2015 | 2005 Ford Focus

1 Answer

I have a 2006 Pontiac g6 gt and my heat or air will not turn on or rear defrost


You have a computer controlled HVAC system ! It has the capability of setting DTC'S - diagnostic trouble codes !
The HVAC control module is a non-GMLAN device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive and ignition 3 voltage circuits provide power to the control module. The HVAC control module during defrost mode will change the A/C compressor LED status from on to off. The control head displays recirc, outside air, A/C and rear defrost feedback status through LED indicators. The control head has a rear defrost request switch please refer to Rear Window Defogger Description and Operation in Stationary Windows for operation. The HVAC control head will display NO COMMUNICATION when checking DTCs or doing a vehicle diagnostic system check refer to Diagnostic Trouble Code (DTC) List - Vehicle and Diagnostic System Check - Vehicle in Vehicle DTC Information.
The rear window defogger system consists of the following components:
?€¢
Body control module (BCM)


?€¢
Heating, ventilation, and air conditioning (HVAC) control module


?€¢
Rear Defog relay


?€¢
Rear window defogger grid


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

May 06, 2015 | Pontiac Cars & Trucks

1 Answer

Why will not switch from vents to floor or defrost


your problem is a mode door actuator located on the hvac case. they all go bad from time to time set a hvac code and system goes into default mode.

Mar 03, 2015 | 2000 Pontiac Bonneville

2 Answers

Why is my rear defrost not working


Switch, fuse or maybe the wiring to the window has come loose or off, happens alot, kits are available at local auto parts stores...
I hope that helps...

Mar 02, 2015 | 2008 Chevrolet Malibu

1 Answer

What options do I have to fix my A/C problem in my 2010 GMC Acadia SLT?


Automatic or manual HVAC ?
Air Distribution
The HVAC control module controls the distribution of air by the use of a mode actuator. The modes that may be selected are:
• Defrost
• Defog
• Panel
• BI-Level
• Floor
The mode actuator is connected to the mode door 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 door 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 door actuator. 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.

On the automatic HVAC the whole dash does not need to be removed !
Caution: In order to avoid actuator damage, DO NOT apply power to the actuator when it is not installed in the HVAC module.
Preliminary Procedures
Remove the instrument panel insulator - right side. Refer to Instrument Panel Insulator Panel Replacement - Right Side.
Remove the instrument panel (I/P) compartment. Refer to Instrument Panel Compartment Replacement.
1
Mode Actuator Screw (Qty: 3)
Caution: Refer to Fastener Caution in the Preface section.
Tighten
2 N·m (18 lb in)
2
Mode Actuator
Procedure
Disconnect the electrical connectors.
Re-calibrate the right temperature actuator. Refer to Actuator Recalibration.
The dash doesn't need to be removed for manual HVAC either ! Take out the glove box an the insulator panel ! Do you know what the insulator panel is ? There could be a video on youtube ! This repair would only take a half hour at most .

Jun 01, 2017 | 2010 GMC Acadia SLT-1

1 Answer

Air not blowing out of vent on 1999 chevy suburban


MODE SELECTION IS VACUUM OPERATED. DEFROST AND FLOOR ARE A DEFAULT MODE WHEN SYSTEM FAILS. YOU HAVE A VACUUM LEAK, FAULTY VACUUM SWITCH ON DASH CONTROL UNIT OR A BAD VACUUM MOTOR IN DASH

Jul 21, 2012 | 1999 Chevrolet Suburban

1 Answer

No air coming out the dash vents. Air does come out the floor vents and defroster vents


{: ) You didn't mention which vehicle model you have, but anyway, check and make sure your control setting is not on defog or defrost. When the HVAC system detects a fault or inconsistencies in the actuator feedback circuits, the HVAC module will default the position of the mode actuator to the floor vents. Usually the fault is caused by the mode actuator itself, or it could be that the actuator doors are blocked or binding, and wiring or terminal connections come next on the list.
If it is an actuator door issue, the HVAC Blower Module should be removed and disassembled. And this also means removing the whole instrument panel which is a big job. I just hope your case doesn't go this far.
For the meantime, what you can try is to recalibrate the actuators. Turn a/c and ignition off. Turn ignition on and wait forty seconds ( don't move any HVAC controls during this period). Afterwards, you may start the engine and check operation. If not successful, a scan tool is the next option, to retrieve any codes set, and to perform actuator recalibration.

Jul 15, 2011 | Chevrolet Silverado 1500 Cars & Trucks

1 Answer

Car air condition works fine but only blows from the floor vent but not the dash vent at all what causes that problem.


{: ) Review again your climate settings, make sure sure it's not set to defrost or defog if you need that a/c on the dash face vents. If you felt that the a/c is cooling fine, then the problem is in the air distribution. It is possible that the HVAC actuators are not responding to the HVAC settings as requested. When the system detects a problem in one of the actuators, it will still try to execute the request but if not successful, it will assume a default position, which is the floor vent position.
There could be a binding door, a faulty actuator, or the wirings. Very seldom for the HVAC controller to be the cause, though also possible.
Normally when you turn ignition on, the actuator system self calibrates itself, say around forty seconds. That's why sometimes you may hear sounds within the dashboard. That's part of its normal functions. Try top turn ignition on or start the engine, but don't activate yet your a/c till after a minute. If that doesn't help, a scan tool may be needed to recalibrate the actuators.
If not successful in the recalibration, then proceed to deeper diagnostics and inspections. I hope you get lucky, and be spared of a possible dashboard removal.

Jul 05, 2011 | Buick Park Avenue Cars & Trucks

1 Answer

The heat will only come out on the floor setting not the vents or defrost


Check for a faulty vacuum line coming from the engine compartment to the hvac system under the dash.Normally they will default to defrost but you never know without seeing it in person.Hope this helps,
Ken

Oct 08, 2010 | 1996 Chevrolet Suburban

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