1999 DODGE CARAVAN HEATER FAN WORKS SOMETIMES IF YOU PLAY WITH IT

Most likely neither. The most common cause is that an electrical device called the blower motor resister block, has failed. This device provides all the slower speeds. It is generally mounted in the HVAC [Heating, Ventilation & Air Conditioning] box, very close to the blower motor. FYI, we mechanics call the fan motor inside the cabin the blower motor. The electric fan motor behind the radiator is called the cooling fan motor.
If the resistor block is OK, then you have either a bad fan speed switch or a melted electrical connector at that switch. 95% of the time, the resister block is the problem.
Charlie

as per this remote discription, fan has a proble with bearing, and as it is an electrical integrated fan unit, you'll need to buy the cooloing fan ***., install it as plug & play!
this link might give you an idea about costs!: https://www.dodgeparts.com/oe_parts_catalog.html

Chances are it is in fact not the switch. These systems are wired so that at high speed setting battery power is connected directly to the fan. However lower settings switches through a set of resistors. These are mounted on a circuit board which in your case is mounted on the firewall on the passenger side of the vehicle under the wiper. Check this before you turn the control panel into a heap of spares on the garage floor.

If you can access the switch contacts Clean them . They become coroded or out of contact with moisture condensation and gunk sometimes

see if you can get access through dashboard

he temp or the fan? if it's the temp, there is a vacuum advance issue. if it's the fan speed, the switch needs to be replaced. the resistors burn out.

blower fan speed resistor module!

Check the heater resistor block in the heater housing. It controls the other speeds.

this problem is caused by a defective fan speed control resistor. This part is located in the air duct work next to the blower motor.
see photo.

If you are looking for the fan blower resistor, it is located behind the glove box. No tools need to get to it and a nut driver to remove the 2 screws to replace it. A 20$ part.

THE RESISTOR OR FAN ITSELF