Question:  The heater in my 99 Jeep Wrangler 4.0 works great, blows lots of hot air, but the windshield defroster seems like it is barely blowing any air against the windshield.  Is this normal?  I have looked for obstructions and do not see any, and the switch seems to be functioning normally, switching between the different locations.  Any suggestions?

**edited to add that the fan is blowing full blast, i just can't feel where all the air is going.  It sounds like it is blowing "in" the dash**

yes, that is exactly what happens, it works fine on low but then makes a loud pop sound when turned up on high like something is popping shut and blocking air  

I lost that guys reply when they upgraded the message boards.... hmmm

Anyone else experience this issue with the defroster?  

I have the same exact problem with my 97 TJ. Haven't put any real effort into fixing it.  

Fixed mine:  followed the instructions below taken from this post:

http://www.jeepforum.com/forum/showthread.php?t=66176


First - Let's look at the vacuum actuators.

1 - Get your head underneath the paneling on the drivers side - this is not fun, but you'll see where I'm going once you get there.

2 - there are 3 silver "cans" with 2 hoses on each one, and a lever coming out of one end - these are your actuators

3 - Start the engine, set the brake and find a friend - you can do this by yourself but it's a PITA.

4 - Turn the fan on LOW

5 - Move the selector lever from one setting to the next SLOWLY! Give it time to settle. As you move the control, the "cans" should move in and out, but they don't all move at the same time for each setting (top one is for the defroster, I think the bottom is for the floor vents, and you can guess what the middle does.)

6 - Check all the selector positions - if none of them move, then you have a vacum leak. If this is the case, better go find a vacum gun and figure out which one is broken.

If by chance you don't have a vacum leak, it COULD be the actuator cans themselves - they have a rubber diapraghm that potentially could break and cause it to not work.

Alright, if you've determined that the actuators work, time for the tough one.

This is to check the actual control arms.

1 - take off the plastic panel under the steering wheel
2 - take off the metal plate behind that
3 - find a flashlight (worklight on the floor of the jeep works too)
4 - Turn on the engine
5 - Move the control slider to the different settings, and watch the moevement of the arms coming off the silver cans.
6 - if the arms move, but the black plastic levers don't, they are broken.
7 - to remove a broken plastic thingy, there's two methods
7A - take the silver vacum actuator off, and grab the plastic arm with a pair pf pliers and pull really really hard straight out. It'll pop off eventually
7B - if it's like mine was, then the arm broke off inside where you cant grab it it get's even tricker. Get a really long decking screw or similar and drive it straght in. Grab the screw with the pliers and pull
8 - finding a replacement is tough - there's a jeep recycler on line (can't remember who it was, I'll go look when I get home) that MAY have these. If you go to the dealer, they'll look at you like you have 4 heads and try and get you to buy a whole new "Blender Box" which is what the heating system is refered to. DON"T DO IT. You only need the plastic arm, but even that will set you back $25 from a recylcer.

For some reason, these plastic things break all the time, and Jeep doesn't offer an "Off the shelf" replacement part. Stupid stupid stupid. If I had an injection molder, I'd start making them and selling them!

Hope this helps.
--BN  

Just took a look under the dash, and sue enough, Broken arm. Noe only is it broke, it is missing!