90 Spirit A/C Heating Problem

I've got a 90 Dodge Spirit 2.5 4cyl, and I cannot get AC or heat. The blower fan will spin when I turn the AC on, but it will stop and start all the time. Nothing comes out of the vents, AC or heat. All the fuses and relays are good, and I recently changed the coolant temperature sensor. Any ideas??? Winter is coming and I dont want to be stuck without heat. Thanks

I have also been told that the resistor for the fan or heater controls could be out. Where can I find this?? Please Help!