1994 Dodge Caravan white smoke coming from heating vents

I have a 1994 Dodge Caravan with about 225000 miles, which I would like to hang onto for a little while longer. The problem is that while the car is running, a while colored smoke is coming from the heating vents. Itg smells like antifreeze. Someone told me it may be a part under the dash that has something to do with filtering the antifreeze that is used to heat the inside of the car. If this is true, could you tell me what part that would be. I'm planning to take it to a mechanic to see if the cost justifies me getting a car of this age fixed. Thanks for your help.