I have a 98 Ram 4x4. No matter where i turn the dial, I only get air to come out the defrost ports only. What could cause this? What do I need to look for to fix this?

 

You have a vacuum leak or need to replace the check valves that control the vents. Do a search for "wild vents" and you'll find what you're looking for.

 

i have same problem. mine is a vaccum leak by the compressor where it goes into the firewall when they installed my new dash they broke the line. now its a small piece that i have to attach another line to it and back to where it goes. check ur passenger side vaccum lines and look for a line not hooked up and look for a leak. mine went to a whole lot of lines leading to the intake manafold and that small leak caused my truck not to run 100% i still havent fixed it but i really dont use my ac. but i did close off the leak and my truck runs a whole lot better and my power is finally back! all my mods ive done i havent felt a increase cause of that leak after i sealed it off i was like WOW