Defrost vents are sticking

Tiny
WRA357
  • MEMBER
  • 2001 JEEP GRAND CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 1,220,000 MILES
My vents are sticking in the defrost position, no matter where you put the control. I have good cold and hot coming from either one. But it will not switch from the windshield area.
Do you
have the same problem?
Yes
No
Tuesday, August 4th, 2020 AT 9:07 AM

10 Replies

Tiny
MOTOR MASTER
  • EXPERT
Hello my name is Dave.

It sounds like you have lost vacuum to your HVAC, without vacuum all you will have is defrost. I tried to find a diagram however the vacuum line going to the HVAC controls from under the hood will have a check valve that looks like a small disk somewhere in the line, it will also have a vacuum accumulator which usually looks like a ball that the vacuum line goes into after the check valve and from there it goes into the firewall, usually on the passenger's side.

I would recommend starting the engine and listening for the hissing sound of a vacuum leak and follow it to the problem. If you don't find it under the hood there is a chance it is in the dash. Another way you can find a vacuum leak is to use brake cleaner and spray around the engine until the engine sound changes however you must be careful as most brake cleaners are flammable which is why it works to find the leaks so only spray small amounts at a time.

I hope this helps you track down your issue and is you need more help please don't hesitate to ask. Please keep us up to date on your progress and thank you for using 2CarPros!
Was this
answer
helpful?
Yes
No
Tuesday, August 4th, 2020 AT 10:07 AM
Tiny
STEVE W.
  • EXPERT
That sounds like either the mode control actuator failed or the linkage arm has broken, both are common failure modes. The location of the control(s) depends on which system you have. Either manual or the automatic controls as shown in the first image If you have the up-level option where you have a temperature selector for both sides, that version uses an electronic actuator that is mounted to the passenger side of the HVAC housing behind the central brace for the instrument panel as in the second image. You remove the brace under the dash to get to the actuator and the linkage.
If you have the 3 dial control with only one temperature control it becomes much more difficult as it uses two different actuators to control defrost. To access both you need to remove the HVAC case from the vehicle. Before doing that I would do some testing to be sure it isn't just a bad vacuum line or control. Do you hear any hissing while selecting the floor or other modes?
Was this
answer
helpful?
Yes
No
Tuesday, August 4th, 2020 AT 10:37 AM
Tiny
WRA357
  • MEMBER
  • 2001 JEEP GRAND CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 1,220,000 MILES
Where is the defrost actuator located on the vehicle listed above?
Was this
answer
helpful?
Yes
No
Tuesday, August 4th, 2020 AT 12:24 PM (Merged)
Tiny
ASEMASTER6371
  • EXPERT
Good afternoon,

I attached the instructions below for you for the actuator.

https://www.2carpros.com/articles/replace-blend-door-motor

What is the issue with the actuator?

Roy

REMOVAL
Heat/Defrost - Panel/defrost Door Electric Actuator

WARNING: on vehicles equipped with airbags, disable the airbag system before attempting any steering wheel, steering column, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (ground) cable, then wait two minutes for the airbag system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the airbag system. Failure to take the proper precautions could result in an accidental airbag deployment and possible personal injury.

These actuators are used only on models equipped with the optional Automatic Zone Control (AZC) system.
1. Disconnect and isolate the battery negative cable.
2. Remove the two bolts that secure the center instrument panel support bracket to the left side of the floor panel transmission tunnel.
3. Remove the two bolts that secure the center instrument panel support bracket to the instrument panel.
4. Remove the center instrument panel support bracket from the vehicle.

Fig.18 Heat/Defrost - Panel/Defrost Door Actuator
imageOpen In New TabZoom/Print

5. Unplug the wire harness connector from the heat/defrost - panel/defrost door actuator.
6. Remove the three screws that secure the heat/ defrost-panel/defrost door motor to the HVAC housing.
7. Remove the heat/defrost-panel/defrost door motor from the HVAC housing
Was this
answer
helpful?
Yes
No
Tuesday, August 4th, 2020 AT 12:24 PM (Merged)
Tiny
WRA357
  • MEMBER
I'm not sure what is wrong with the controls. I hit the button to turn the air on and it stays on defrost. No matter where you put the knob. I took my glove box out and panicked because I had no idea how to put it back. I finally got one of the two rubber pieces back in and the other isn't in correctly, but it's holding so I shut it and stopped doing anything to it. I do not know anything about the actuator, but it sounded like that had to be my problem, so that's why I asked about the location of it. I am willing to try anything to get it fixed without costing me a ton of money.
Was this
answer
helpful?
Yes
No
Tuesday, August 4th, 2020 AT 12:46 PM
Tiny
STEVE W.
  • EXPERT
Which controls do you have the manual control or the automatic? Makes a big difference in the next steps.
Was this
answer
helpful?
Yes
No
+1
Tuesday, August 4th, 2020 AT 1:14 PM
Tiny
WRA357
  • MEMBER
Manual.
Was this
answer
helpful?
Yes
No
Wednesday, August 5th, 2020 AT 6:49 AM
Tiny
STEVE W.
  • EXPERT
Manual controls means your vehicle uses vacuum actuators for the mode controls instead of the electronic ones. It uses an electronic one for the temperature only. You say you have hot and cold control but cannot switch the air from defrost to floor or dash correct? In that case I would first start by starting the engine then listening inside the car close to the dash for any hissing sound from a broken or loose vacuum line, it will be very faint but you may hear it. Next would be to look under the hood for a broken or loose vacuum line, normally if it was off you would have a slightly higher idle but not always.

If you hear no leaks the next step starts by removing the trim pieces above and below the heater control panel so you can access the screws that hold the panel in. They are held in with trim clips and you remove them by prying the clips free with a trim stick. Once the trim is out there are 4 screws that hold the control head in place. Remove those and pull the control head out. With it out you will see the vacuum lines from it and the connection they make to the vehicle. Disconnect the vacuum line connection only, not the electrical connection. Now you will need a hand held vacuum pump with a gauge on it.
With it you can test the system to see if it is a bad actuator or the control head by using the gauge to check for vacuum at the black hose that you disconnected from the control head. If you have vacuum there then you can use the vacuum pump to apply vacuum to the Brown and yellow hose nipples. Those control the defrost actuators. With the key on and the blower on you should be able to change the airs movement if you apply vacuum to each fitting. Now you can also watch the gauge on the pump. If you apply vacuum to say the Yellow line and it shows a vacuum but the airflow doesn't change it is likely the linkage is the problem and not the actuator. If however you start pumping and nothing happens and the gauge doesn't move it is either a bad vacuum line or bad actuator. That will require further work. Unfortunately on this vehicle it means the dash assembly has to be removed to be able to access the HVAC case and remove it because the actuators are between it and the firewall.
Was this
answer
helpful?
Yes
No
+1
Wednesday, August 5th, 2020 AT 9:27 AM
Tiny
WRA357
  • MEMBER
Thank you for your advice. I forgot to mention this; for a while when it wouldn't let me switch the setting from defrost to anywhere else, (if I turned the control up for the airflow) you could hear something rattling really bad, like something was in there flipping around. It doesn't do that anymore. It's like it landed somewhere and stayed there. I'm going to run into town and try to buy a hand held vacuum pump and try to get these steps done.
Was this
answer
helpful?
Yes
No
Wednesday, August 5th, 2020 AT 12:25 PM
Tiny
STEVE W.
  • EXPERT
That isn't a good sign. It could mean the air door inside the case failed and that is what you were hearing moving around. Or it might be that something fell into the defrost vent and made it into the case and is jamming the door. Might be worth it to use one of the lower priced inspection camera units you can get for a laptop or phone to look inside the unit before you take it all apart only to find you could have moved or fished the item out from above. It's a long shot but still less work than pulling the entire thing apart.
Was this
answer
helpful?
Yes
No
+1
Wednesday, August 5th, 2020 AT 12:48 PM

Please login or register to post a reply.

Sponsored links