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2002 GMC Envoy. AC fan stops completely. When moving position switch to defrost or front and foot position it sounds like a something is clicking in the vent.

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  • Cars & Trucks Master
  • 20,706 Answers

Which fan, there are 3 to 4 fans.
saying fan means zero. on cars.
did you know on modern car the PCM cranks up all fans ? on A/C demand? not just 1.?

my guess, the Dash heater/A/C HVAC blower fan dies. in the dash?
The dash sections here, have dampers.
they work one of 3 ways, vacuum, cables or motors. (or mixed)
the FSM covers this.
the damper can fail many a way, as can the fan and there controls.

A/c stops???
please tell what that means, sure cold air stops.
we get that.
but does the main blower work. at all speeds.>
if the blower stops the A/C air stops but also
the compressor goes offline (clutch)
if 12v power reaches a dead blower motor the compressor does not know this is true and keeps going, so if car is moving air does flow
non recir, and it does get cold, proving A/C works.
see?
The air flow is it stopping with blower making its normal air sound?
im guessing you are not taking the 3 fans on front end of car.
2 for engine rad fans and 1 more in front of A/c Condensor.
im not logging in to alldata.com to see fan counts.

the car came new with 2 HVAC options, automatic and manual.
im not guessing that either
the car came with optional aux blower too. long wheel base car>?
login to alldata.com and see this very complex system.
(get it serviced?)
here is one excerpt of the Manual system Acutators.
see this level of complexity, and the scan tool tests (dealer)
Auxiliary HVAC Control Module
The auxiliary HVAC control module is a class 2 device that interfaces between the rear seat occupants and the auxiliary HVAC system to maintain auxiliary air temperature and auxiliary air distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all auxiliary HVAC DTCs and settings will be erased from KAM. The auxiliary HVAC control module will perform a recalibration of the electric actuators when commanded with a scan tool or if KAM is lost. This will ensure the actuators are moving with in the calibrated range. During this calibration process the auxiliary blower motor will be disabled for up to 3 minutes.
Defrost Actuator
The defrost actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.
The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.
Mode Actuator
The mode actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.
The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.
Auxiliary Mode Actuator
The auxiliary mode actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, 5 volt reference, position signal, and two control circuits enable the actuator to operate. The control circuits use either a 0 or 12 volt value to co-ordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the auxiliary HVAC control module grounds one of the control circuits while providing the other with 12 volts. The control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.
The auxiliary HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, one of the control circuits is grounded. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module grounds both control circuits.
Auxiliary Console Mode Actuator
The auxiliary console mode actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, 5 volt reference, position signal, and two control circuits enable the actuator to operate. The control circuits use either a 0 or 12 volt value to co-ordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the auxiliary HVAC control module grounds one of the control circuits while providing the other with 12 volts. The control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.
The auxiliary HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, one of the control circuits is grounded. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module grounds both control circuits.

if a real DIY person, why not buy the FSM and not try to work ALL THAT and more blind.?

Posted on Jun 18, 2014

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6 Suggested Answers

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Posted on Jan 02, 2017

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SOURCE: 2004 Envoy AC works but does not come out the front vents. Only @ windshield

You most likely have a bad mode actuator. http://forums.trailvoy.com/showthread.php?t=40235

Posted on Sep 26, 2008

  • 8 Answers

SOURCE: 2003 dodge caravan air vents will not change position?

I HAD THE SAME PROB WITH MINE I REPLACED THE HEATER CONTROL PANEL & IT FIXED IT

Posted on Mar 07, 2009

csmock132
  • 4669 Answers

SOURCE: 2004 GMC Envoy; Very little air flow from FRONT PANEL

Try replacing the cabin air filter.

Posted on Mar 12, 2009

abauto
  • 353 Answers

SOURCE: 2002 gmc envoy shuts off when i turn on the ac whil ideling

If it does it when idling I would suspect an IAC motor (Idle Air Control). If it is opening too slowly the added air the motor needs will not be supplied fast enough and the engine will kill.

It could be other things also but this is where I would start.

Posted on Jul 27, 2009

  • 460 Answers

SOURCE: I replaced heater core in 1999 gmc sierra 1500 5.3

no,, the system works from a vacuum and has to be worked on in a service garage. sorry about the bad news...

Posted on Nov 12, 2009

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