2000 Dodge Caravan my air is not gettiing cold

First, the coolant has nothing to do with the AC. And as far as the coolant, chrysler used their own type. You can get a universal G-O5 coolant that will work with all types, but you shouldn't mix the OEM with traditional green type.

Now for the fan, if it only works on high, you need to replace the blower motor resister. Is isn't an expensive part. It is located on the HVAC system under the dash. Unplug the old one, unbolt it and replace it with the new one.

Let me know if you have other questions. Also, if the AC isn't working, chances are it needs recharged. However, if you are getting heat when you have it on AC, then the blend air door isn't working.

Joe