Not sure about the ZJs but I know in the WJs the defrost is a default mode. As in if anything goes wrong with your heater stuff the vehicle is programmed to automatically go to defrost that way your toes may be freezing but you'll have a clear windshield to see out of.
I have somewhat of the same problem in my 02 sport, except my heat and air work but only come through the dash vents and nothing through defrost of bottom. Would this be the result of the same vaccum hose problem?
Cowboy, if the system in your is anything like it is in mine, no. There's a motor driven cam wheel in behind the heater controls that has three pushrods that go through it. The pushrod for the "face" vents pops out and has to be manhandled back in. And since the "face" vents are the shortest for airflow, the air takes the path of least resistance and none gets out the upper or lower vents.
You have a disconnected or cracked vacuum hose under the hood, probably around the throttle body area. I'm betting your cruise control doesn't work either does it
Okay, I found this forum last night (12/2/09) looking for an answer to this question. When I read your comment about the cruise control not working, I almost fell off my chair. It had never occurred to me that they were related. You're good. Thanks for the info. I need to check all my lines, 'cause it's getting colder in Utah, and I want to be able to feel my feet, not just my forehead. Cheers!
One other place to check is look under the dash on the drivers side. If you look towards the glove box, there is a plastic white arm. It is right behind the message center. The lever breaks right by the eye that connects it to the shaft. If it is broken you will only get light defrost and heat. Just my 2 cents. Also there is an arm right under the ignition, try to push that up manually.
This is exactly the problem that I have - heat, defrost and only low. I looked for this lever but could not find it. I have a 98 cherokee. Please help.
Hey everyone. I realise this is an old thread, but I had the same problem. Ken, I nearly fell off my chair too when I read your answer
about the cruise not working as well. Anyway, I read all the posts on the subject and decided to have a look under the bonnet again.
To my joy, I found a small rubber pipe had popped off of its connector. I dont have a clue what it does, or what its called'
but air blowers and cruise are working just fine now! Id just like to thank you alk for your informed answers, and indeed questions.
I have attached two pics to show the location of the offending item. Hopefully they will help other hapless amateurs
such as myself!