Diagnosing ACC II climate control problems can be difficult, depending on the symptom. In general, suspect the dash-mounted control unit last.
Some things are easy, like if the fan runs full speed, even when the ignition is turned off - that's a shorted transistor in the blower controller. The only way to make it stop is to pull the fuse or disconnect the connector at the blower motor. Replacing the transistor in the blower controller will fix that - see here.
Blower doesn't turn at all: First, check the fuses. Next, try wiring the blower motor directly to the battery, as described in the next paragraph. If it runs OK then, check the connector on the blower controller. If that's OK, try replacing the transistor in the blower controller. If that doesn't do it, then it's either a wiring fault or the dash-mounted control unit.
Erratic fan operation: Hard to diagnose - could be the blower motor itself, could be the transistor in the blower controller. I've had both cause the symptom. Could also be the ACC II control unit in the dash too, I suppose, although I've never had any trouble with that. Try disconnecting the connector at the blower motor and wiring it straight to the battery (use reasonably large wire, as it draws a lot of current - standard household lamp cord would probably do for a brief test). If the motor runs full speed without any hesitation, try whacking on the blower housing. If it still runs without a hiccup, that's at least a good sign that it's probably OK. Try replacing the transistor - that fixed erratic operation once for me. Check the connector at the controller first - the early models tended to corrode and even melt sometimes. If none of the above, it's either a wiring fault or the dash-mounted control unit.