What can i do?

Sounds as if the problem is in the climate control panel. The panel may have a bad circuit board that is dropping signals to the components you are trying to operate.

If the fuse is good then look at the turn signal switch on the column. 99% of inop signals are caused by the switch. If the fuse blows only when you apply a turn signal with the switch, there is a pinched wire or a short in the turn signal wiring.

It should only be a slight loss of power. This is caused because the defroster also turns on the air conditioner which uses dry air mixed with the heater air to defrost the windshield.

it sounds like your heater core is leaking. Check to see if your coolant level is low. A radiator pressure test will show a leak. coolant may be dripping down from the heater air box drain hose. Replacement of the heater core is expensive. you can bypass the heater core, to keep you on the road, by looping one of the heater hoses back to the engine....but you will have no heat. Here are a couple of sites for reference;

http://www.2carpros.com/forum/1999-dodge-dakota-heater-core-vt214043.html

http://dodgeforum.com/forum/1st-gen-durango/18340-heater-core-removal-installation.html

a couple of things,1 blower motor fuse.2 blower motor gone out.3 switch on fan speed control switch not sending signal to fans.after checking the fuses.next check theswitch on control panel.set ac or heater.if fan still doesnt come on then replace it.when it work and then stops working there are a lot of possiblities that caused the prob relay too not fliping over inside staying close loop.hope this helps.

There are no defrosters on the sliding doors.

Probably broken blend doors if everything else is working, but its just blowing cold air. Do a google search for "Jeep Blend Doors" or "Heater treater" for more info.

when your car is in defrost it has an ac cycling it removes the moisture then sends the air over the heater core depending on how warm you set it you can feel warm or cold but the ac is always cycling...ridding the moisture...you need a good ac tech it will be okay...its just expensive going into the heater core if needed...!

It sounds like you have a bad temp door actuator.

you need to begin by changing the thermostat. if you dont know how go to an autozone and they will assist you.

if that doesnt solve the problem you need to change the heater/ac blower relay.