NCDON

Old problem, only the drivers side defroster is blowing and I would like to figure out what the problem is.


This is a 1999 XJ

JamromXJ

Pop-out the center radio/HVAC control bezel... remove your radio.

Right behind the radio, after you move the wires aside, is the door flap that channels the air towards the defroster/defog plenum. When you select 'Defrost" the flap will open.

Make sure the flap opens and closes properly and that the plumbing is not jammed with anything on the passengers side.

It's really that simple of a system.

JR

NCDON

My Jeep is a 1999 XJ.


I popped the cover off and removed the radio. Turned the fan on high and then tried the **** in all non AC positions, this is what I found.


Front vents. Good air flow


Floor Heater. Good air flow


Defroster. Defrost door not opening to allow air to defroster vents. The air I was getting on the drivers side is just a little air the passes by the closed door. I did manually open the door with my finger and BAM a lot of air flow, when I removed finger the door closes quickly.


Defroster/Floor Heater. No air flow.


The flapper door at the defroster only opens and closes in the front vent and heater position.


So, my defroster and defroster/heater combo switch locations do not send air to the intended locations, any ideas how to correct this problem?

freegdr

Search Blend door actuator.

mikjensen

I had a similar problem and found a leaking vacuum line under the hood. Loss of vacuum was preventing actuator from moving enough to allow defrost.

NCDON

Gentleman,


Additional questions.
With ignition off the defroster door is open.
Ignition on, defroster door is open. (Location Control **** off position).
Ignition on and location control **** in any position, defroster door closes with force.


Would it be a correct assumption that I do not have a vacuum leak since the defroster door snaps closed very fast with force and an auditable sound?
the
My understanding is the defrost flapper is vacuum operated, seems it would close slowly or not at all if there was a vacuum leak but what do I know.


Hoping to understand which approach I should take, vacuum or replacement of Blend door actuator.

CCKen

Here's some pics you can study:

NCDON

CCKEN,


Thank you for the diagrams and pictures.


It appears the dash would have to be removed to check the 3 vacuum actuators to assure they are operating, connected and operating. These actuators are called vacuum actuators but in the picture I only see an electrical connection?


The picture of the control switch's leads me to believe you are suggesting I check for voltage at each setting, is this correct? If so I will attempt to check this weekend if I am not working.


I was just looking at the vacuum line and it seems to come out of the firewall then "T" with one leg going toward the in a long rigid Where will the other end of the "T" connector lead me to?


Am I on the right track?

JamromXJ

your 99 has the HO intake, which if you look at the drivers side of the engine, right next to the power brake booster, you have three small vacuum connections. That's all the vacuum your XJ needs. It all comes from there. The booster has it's own on top as well as the CCV port.

The middle one is the source vacuum for the cannister in your front bumper on the passenger side (ball accumulator).

Check that all three are connected and that the lines to and from all areas in the system are connected and not leaking.

JR

CCKen

https://picasaweb.google.com/ken384/...eat=directlink

CCKen

Referring to the vacuum functions schematic above -


Note that in all mode selector positions except 5 (Defrost) and 6 (mix), vacuum is applied to the defrost door actuator to close the Defrost Door.


In the Mix position the defrost door actuator is driven to the mid position (Blue tube), and the floor door actuator is driven open.


The Defrost Door Actuator is spring loaded to the door open position and it takes vacuum to close the door or move it to the mid position.


With the engine turned off (or the Mode Selector switched to OFF) and vacuum is still trapped in the system the Defrost Door will be closed. As the vacuum in the system bleeds off the Defrost Door will open.

NCDON

To date I have viewed the connections at the mode selector, all are connected and seen tight. Looking under the hood at the intake there are three vacuum ports on the side, the far left is capped, the center one was slightly loose so I applied orange RTV to seal it, the right one fits tight. All the rigid piping appears to be intact, no rub marks found.


This weekend I hope to be able to check the ball accumulator, I know where it is but will I be able to check it on my 99 from under the jeep or do I have to take anything apart?


What else am I missing?

CCKen

As you stated in post #3, your other door functions work so I don't think there's a vacuum leak in the engine bay.


Maybe you should focus on the defrost door actuator vacuum tube connections, or that the actuator is defective,


As far as accessing the vacuum reservoir goes, you can either remove the right front bumper end cap to get at it, or lay on your back under the right end cap, and pull the right wheel well liner down at its front edge. You can see the vacuum tube connection using a flashlight.

NCDON

After nine months I spent more time on the problem of not getting heat to the drivers side defroster. Looking into the possibility of a problem with the defroster door actuator, I confirmed the actuator is working but I found the defrost door linkage is broken.

Looking at the FSM it appears the dash has to be taken apart to repair or replace the linkage or door.

Anyone have a better way, I am open to suggestions.

CCKen

Nope.