If you own a Z3, eventually the blower motor for the air condition will either work at max speed or no speed. The way the circuit is wires the motor speed is controlled by a resistor pack that is attached to the motor, depending on the lead that is energized it will turn the motor the corresponding RPM. 0 obviously being off, and 4 being MAXIMUM rpm. 1-3 is a current variation to vary the rpm. Due to its location within the blower compartment eventually they fail either through dirty leads or just wearing out.
There are two trains of though here, replace it entirely or the contacts are just dirty. I’ve heard positive feedback that just a good cleaning and reinstallation solved the issue but I already had new parts so I replaced and am keeping my original as a spare.
I had started to experience intermittent issued to exactly that effect years ago. I preemptively bought a resistor replacement and then proceeded to sit on it for 5ish year (note: apparently these have nearly tripled in price since I originially bought it, I’m not sure I wouldn’t try cleaning it first at today’s pricing). This year was finally the year I replaced it. Access to the resistor pack is through the windshield cowl and into the blower motor compartment.
Tools:
- Plastic pry tool(s)
- 16mm wrench/socket
- Long handle pliers
- Puller tool (optional for windshield wiper arms)
Material:
- Blower resistor pack (optional), PN 94116912633
1) I removed the pair of windshield wiper arms to gain unobstructed access to the cowl for removal. It’s important to mark the position relative to the spindle to ensure they are reinstalled in the same position. I marked mine with a wax pencil, but I’ve previously also laid a piece of tape on the windshield aligned with the wiper blade to reposition it at reassembly on other vehicles. The arms are removed by removing the beauty cap covers, removal of the 16mm nut, and pulling the arm of the spindle. They can be difficult but should come off with a little persuasion.
2) Remove the windshield cowl weather strip to the hood
3) With my pry tools I removed the 8 press fit expansion fasteners
4) Remove the cowl and place out of the way. There are two tabs that are under the FWD/AFT weather strips on each side that will need to be uncovered for removal
5) The blower box is secured via two plastic straps, very careful (aging plastic in play here), disconnect the two straps and remove the blower cover
6) With my long handle pliers, I removed the old resistor pack with a slight yank.
Some other Z3 friends have reported a good cleaning of the contacts on the existing unit fixed their intermittent speed issues. 
7) Reassemble in reverse order (after testing your repair has restored the fan speeds).
Double Bee Garage 
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