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2008 Grand Cherokee 4.7L Blend Door Actuator Issue


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cjaveni
User

Nov 11, 2021, 10:08 PM

Post #1 of 7 (563 views)
2008 Grand Cherokee 4.7L Blend Door Actuator Issue Sign In

After hearing a noise in the dash, I have noticed the passenger side was only putting out cold air when I had the heat on. So I figured my air door actuator was bad. When I took the old one apart, I noticed the gear that goes on the actuator had snapped in half as well as the gear that is supposed to be attached to the air door externally. So I tried the actuator while it was unmounted. I noticed with every indent I would turn the knob that it would move incrementally. That was fine.
But when I went to full hot or full cold it would rotate WAY TOO MUCH. Which explains why the parts broke. New actuator also does the same thing so it doesn't seem to be an actuator problem.
My question is, what controls that? What controls how much it moves and why would it go out of range? I know I have to take the whole air unit out to fix all of this now, but cant fix this without fixing what is making it move out of range. Have included pics. Thanks for your help.






(This post was edited by cjaveni on Nov 12, 2021, 12:06 PM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 12, 2021, 5:18 AM

Post #2 of 7 (542 views)
Re: 2008 Grand Cherokee 4.7L Blend Door Actuator Issue Sign In

What you have is a very common problem with Jeeps. It's very common for the door itself to break also so check that carefully.

The actuator is operating normally. You shouldn't be running it full sweep when out of the car. It relies on the stops to calibrate the sweep when it's in the vehicle. When the key is first turned on after the battery is disconnected it goes through a calibration where it sweeps end to end and the resistance against the stops tells the system where to stop.

PS, I made your images show up live in the thread but can you reduce the size of them by at least half. If not I will have to turn them back into links.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Nov 12, 2021, 5:21 AM)


Tom Greenleaf
Ultimate Carjunky / Moderator
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Nov 12, 2021, 5:33 AM

Post #3 of 7 (535 views)
Re: 2008 Grand Cherokee 4.7L Blend Door Actuator Issue Sign In

I looked at those didn't try. Not so helpful, just showed broken was thinking door wrecked was waiting for you Hammer! Tom


cjaveni
User

Nov 12, 2021, 12:00 PM

Post #4 of 7 (521 views)
Re: 2008 Grand Cherokee 4.7L Blend Door Actuator Issue Sign In

Thanks for that Hammer. My question is though, if it wasnt exceeding the stop, why would it snap like that. If you look at the actuator it has a stop. The gear hits that but the actuator keeps going in turn broke the gear on the actuator and the gear attached to the door. If it was working correctly, the gear would have it the stop on the actuator and would have stopped and not snapped??

THanks again for your assistance. Hopefully the change I just made to the pics help.


(This post was edited by cjaveni on Nov 12, 2021, 12:05 PM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 12, 2021, 12:14 PM

Post #5 of 7 (509 views)
Re: 2008 Grand Cherokee 4.7L Blend Door Actuator Issue Sign In

Go into the image software and click on the icon shown for the image you want to resize. 50% should be enough for these.



edit, I see you figured it out

The reason they break is just poor quality plastic. When it goes through calibration mode it hits the stops and as pressure is applied the current draw increases and the module recognizes that and marks the point. Then it does the same thing in the opposite direction.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Nov 12, 2021, 12:15 PM)


Tom Greenleaf
Ultimate Carjunky / Moderator
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Nov 12, 2021, 12:51 PM

Post #6 of 7 (501 views)
Re: 2008 Grand Cherokee 4.7L Blend Door Actuator Issue Sign In

Begs the question - as I've read this a few times now. Did it bust the new actuator again? OR just not operating properly yet?

When this was out appears a round part with two nubs inside or outside runs the door.

Idea is all I have those since all time act like a choke plate sized + shape of where placed with felt or rubber to make final seal will not pass that without usually stopping a motor that knows it.

I'm watching this exact problem new to me. It's computer controlled so does a sweep to know those limits you could tell by hand hopefully without a wild dashboard diving trip I wouldn't want also busting things (plastics) go brittle + goo for cases so stuck together another task to take on possible.

Keep going hope new one isn't busted and might need a scope to see what flap (my name) looks like in there,

Tom >forgive me, cable service has cut out twice today alone where I am<



Hammer Time
Ultimate Carjunky / Moderator
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Nov 12, 2021, 1:17 PM

Post #7 of 7 (498 views)
Re: 2008 Grand Cherokee 4.7L Blend Door Actuator Issue Sign In

Here is the factory's explanation


OPERATION

The blend door actuators are connected to the A/C-heater control through the vehicle electrical system by a dedicated two-wire lead and connector of the HVAC wire harness. The blend door actuator(s) can move the blend-air door(s) in two directions. When the A/C-heater control pulls the voltage on one side of the motor connection high and the other connection low, the blend-air door will move in one direction. When the A/C-heater control reverses the polarity of the voltage to the motor, the blend-air door moves in the opposite direction.

When the A/C-heater control makes the voltage to both connections high or both connections low, the blend-air door(s) stops and will not move. The A/C-heater control uses a pulse-count positioning system to monitor the operation and relative position of the blend door actuators and the blend-air doors. The A/C-heater control learns the blend-air doors stop positions during the calibration procedure and will store a diagnostic trouble code (DTC) for any problems it detects in the blend door actuator circuits.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Nov 12, 2021, 1:18 PM)






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