[fornarog]

Any advice re: this problem with my 99 windstar is appreciated.

Recently, a problem with the heater/ac system has started. There is a steady (1-3 second interval) "thump" (like the noise when you change from zone to zone) coming from the center of the dash, just behind the ac/heat controls. This sound happens regardless of whether the system is on or off, and there is no change between the different zone selections (A/C, floor, defrost,...) If you slide the temperature selector from Hot to Cold, the thump is replaced by a clicking. The temperature selector does not have any resistance to it, and feels like it is sliding freely.

Only cold air is blowing, and it will blow colder when the temp selector is moved to cold, but there is no hot air blowing at all.

Any ideas on what this might be, or how to diagnose the problem?

Thanks