Air conditioner ducting on 89 xj40

(David Martin) #1

Does anyone have a link to an A/C ducting pic that shows where the ducts and baffles etc. are located?

(David Jauch) #2

Honestly, the best trick is to find a few pictures of the unit on ebay, and the manual!:slightly_smiling_face:

(Grooveman) #3

David …

This will tell you EVERYTHING you want to know (and more) about your A/C system.

Just download the link and hit the green “download” box.


As far as the ducting goes it’s very simple. The dash top is basically a long hollow box that acts as the upper duct. The air coming out of the top of the evaporator/heater housing (“air output to dash” on diagram) blows into the bottom of the dash and comes out of the center dashboard vent, the two side dashboard vents, and the two demister (defrost) vents on top of the dash. The two demister vents and the center vent have vacuum actuated flaps that can open or close.

Each of the two bottom ducts coming out of the evaporator/heater housing (“air output to duct”) then separate into two, with one blowing air onto the driver legs and the other side blowing it on the passengers legs. The other two ducts run all the way back through the console to blow air out of the vent at the back of the console.

That’s all there is to the ducting.

By the way I pulled my dash top off a few months ago and made some modifications that dramatically increased the A/C air flow out of the center and side vents. Let me know if you’re interested.

(David Martin) #4

Thanks Gman, I have decided to forget all the jag electronics and after a few hours poking under the dash noticed none of the flaps were moving. I already have the defrost vent locked out, broken actuator, and with a couple proper sized 2×4 I have locked the return air vents for just recirc. Much better volume, outside intake is probably full with rat nesting, I now have 3 fan speeds heat or cool max and it works for me.

(Grooveman) #5

David …

Usually the problems with this A/C system are more associated with the air distribution part of the system rather than the air cooling part.

The air cooling part simply involves cooling the evaporator to just above freezing. This can be easily checked with a good A/C manifold gauge set.

The distribution system however is a bit more complicated and prone to problems such as:

  1. Blockage on the outside of the evaporator face due to decades of blown in dirt and debris.

  2. Malfunctioning recirculation flap doors on one or both of the two blower units, one or both of the demister doors, and the center vent door. This is usually caused by either a bad vacuum actuator or mechanical failure of the door or linkage.

  3. Problems with one or both of the blower units. If one unit fails, because of the way the system is designed the remaining blower provides almost no air flow.

  4. Sticking of one or both of the blend flaps inside the evaporator/heater housing unit.

Being totally frustrated with the lack of adequate cooling, not too long ago I completed removed every component in my entire A/C system and found a problem with every one of the above. Now I’m happy to say my system works perfectly with 38-40 degree temperatures at the vents in the hottest Texas weather with excellent airflow. Actually very little expense just a lot of labor, but to me the end result was well worth it.

(David Martin) #6

What did you do with the dash off(not something I really want to do I hear its a bear) to increase air flow?

(Grooveman) #7

David …

Removing the dash like any job gets easier every time you do it :smiley:

The last time I removed mine it took less than an hour, but then again I’ve probably had it off about 4 -5 times over the years. If you do a little research on the forum beforehand and identify the location of all the bolts and screws that need to be removed the job is very straight forward.

With the dash off you have access to the two demister units (and I’m betting that one or both of yours are not working) and the center vent which also has a high failure rate as the years go on.

(David Martin) #8

I already have the center vent blocked open to the dash and noticed today the other demist bents are leaking to the windshield, I may have a go at dash removal and close them as well so all air goes to dash vents.

(Grooveman) #9

David …

If you decide to remove your dash top let me know and I’ll go into detail about possible repairs of your demister vents and modifications that I made to the center vent and ducting.

(David Martin) #10

Sounds good, easy mods? I notice if i close the center vents a bit I actually get more flow to the side vents, unfortunately most air then just goes to the otherside! Did you make some plenum mods?