Hey all, I was researching this for a friend (Krazy) and I thought I would share the information.
For those of you with 1981-1984 USA-built Rabbits with factory AC, a common HVAC problem (aside from a blown heater motor, and usually in conjunction with a blown motor), is a blown resistor pack. The resistor pack is located on the passenger side of the heater box. To access it, you need to remove the lazy-S shaped duct that gets screwed to the side of the heater box, and serves to direct heat to the floor of the cab. This duct is held in place with either 4 or 6 Phillips screws. The resistor pack itself is screwed to the box with 2 7mm screws, and has 4 terminals on it (not to be confused with the AC cutout sensor with 2 terminals). The easiest way to access the resistor is to remove the glove box, and then you can see everything clearly.
The symptom of the blown resistor pack is simple: Your blower motor only works on high speed. The cause of a blown resistor pack is excessive current draw on the thermal fuse, caused by a worn motor. The fix is pretty easy. All you need to do is remove the resistor pack, and solder (or crimp) in a new thermal resistor.
Here is a link to the procedure for a MK2 car. The idea is the same, but the looks of the resistor are different, and the thermal fuse has a different value:
http://forums.vwvortex.com/showthread.php?2665283If soldering in, I would strongly suggest using a heat-sink to prevent blowign the thermal fuse before you even get to use it.
Radio shack carries thermal fuses, but the values may be too low. The closest they have is 128C, which may blow again if your motor is near the end of its life. You probably don't want to go too high either. I found this site which has the exact thermal fuse required for the 1981-1984 USA Rabbit. The best part is the cheap price, and CHEAP shipping.
http://www.goodmans.net/get_item_th-tf152c_thermal-fuse-152-degrees-celsius.htmFor reference sake, here the original information off the thermal fuse:
Patented Microtemp
4300A1
NTWT 152CGood luck!