Usually if you can't change the fan speed it is stuck on high speed because the resistor pack that controls the speed is bad. Normally the resistor pack is mounted on the fire wall close the fan which is near the AC Evaporator. You should be able to see it on the firewall.
If it is not cooling your system may need to be charged, is your compressor running? You can buy a can of refrigerant ~$30 from an auto parts store or Walmart. This may be a temporary fix if you have a bad leak. I had to add a can of refrigerant to my coach ~5 years ago and it's still cooling.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi