Since so many people have asked questions about the blower working on Level 4 only, I thought an update might be helpful.
The 1989-1994 e34 has two types of blower relays. The first(cheapest to repair) can be found on the later models. The part is a resistor located behind the carpet panel on the driver's side of center console. The part is around $17 and can be replaced in a matter of minutes.
The second type is a limit switch. Also known as the "Sword", due to its shape. This part is attached to the backside of the heater unit. The replacement takes a few extra steps including the removal of the glovebox. Instructions can be found on pages 640-2 and 640-3 of Robert Bentley's BMW 5-Series Service Manual. Goto the "bimmer.org" online store or "barnesandnoble.com" to purchase the book. I got my book from "barnesandnoble.com" in 3 days and cost less then $60 including s/h.
The sword is $273 from the dealer. I got mine from Jurasic Parts for $220 + t/s/h. It is an OEM part w/ a 1yr warranty. Contact Joe and tell him Matthew Lloyd told you to call. If anyone needs a picture of either part's location, email me and I'll see what I can do. Good Luck!
89 535i 223K