What gives? Sometimes it works normal but lately it goes to full heat/defrost and nothing I do will change the setting..Thanks!

Check for a vacuum leak.

Thanks stumpy

does that have the automatic or manual temperature control ? both of these have a self diagnosing feature. if you don't have access to the FSM, let me know, and i can scan a PDF for you. there are no vacuum lines hooked to these controls.

My goof. I thought they still had vacuum operated doors.

stumpy, no problem. and for whatever reason, i decided i could fix a door servo that was broken. i used a couple of spare minivan servos i had laying around. to say that was interesting would be an understatement, but i did succeed using those parts.

moparx, It is automatic and/or off

Just for fun try disconnecting the battery for a few minutes and see what happens when you hook it back up. Resetting the whole system sometimes works.

I unhooked the battery for a few minutes, when I hooked it up and started the engine it blew air through the vents for a few seconds then went to full defrost again, I repeated this twice with the same result.

Full defrost is the default setting.

OK, so what must I do now?

You need to replace the "blower power module". Used ones on E-Bay are about $40. You can pull the fuse temporarily to stop the blower fan.

My 99 CTD has this same feature

The blower power module is only for the blower motor operation as far as I remember. On the auto temp cars the body controller works many of the heat/Ac doors. I have been retired since 2011 so I would have to double check but if auto temp it will have a self diagnose or they can be diagnosed on the Mopar DRBII scanner which we did at the dealer all the time. You can also check TSB's for that year and make sure none under Heat/Ac refer to your problem also. But if you can have it scanned and see if it has a code in that system that may help you fix it. Good luck , Ron

Yup - the brain for the temperature control is shot.

Seems that I may need the entire 'in dash' control unit.???

I had to replace the in dash automatic control a couple times in my 94 LHS.

Some killer diagnostics lead me to the in dash unit. If I give it a good smack it would work fine for a long time. As a harder hit became necessary I unscrewed it from the dash for a real [censored] kicking.

After growing tired of that fix. I replaced it with a used unit. It worked fine for a few more years but when it eventually needed a hitting too.

At this point I opened my original unit and found a crack in a solder trace. Blobbed a bit of solder on top of the crack and it worked again.

Mine needed to be smacked good too but lately that didn't help. I unhooked the battery and two days later it worked like it should...Got my fingers crossed tho.

I had this problem on mine and there is a gear box that controls the blend doors. Its a real pain to replace but can be done without pulling the dash.
Gears strip out and you may hear some clicking coming from it. Located by passengers feet. Get a new one. I replaced mine with a junkyard one and it failed shortly after.