Ok, got ELSA working. I found that the 2001 A6 with the 1.9 AJM TDI engine uses a climate control in the same family as the allroad, if not exactly the same one; they have variants for w/wo heated seats, NAV, etc. The AJM is the only 1.9 I could find that used a compressor clutch rather than the compressor control that Scott mentioned. In addition, Audi made a running change in the climate control in 2002, and I don't know which one he has or if it even makes a difference in the wiring.
Anyway, pin numbers between the BHW and AJM ecu's don't match at all, but wire colors seem to match reasonably well, discounting for differences in the engine electronics.
The A6 climate control shows:
1. sw/ge (black/yellow) going from A7 to the ECU. This seems to match up with the same function as black/yellow on the Passat ecu, terminal T94/85.
2. ws/bl (white/blue) going from C13 to the ECU. Unfortunately, the AJM ecu has multiple white/blue wires. The connection to C13 on the climate control is interesting because it is only noted for diesels. The AJM ecu has white/blue on terminal 61, but that goes to the EGR valve. It also has white/blue on terminal 15, that indicates it goes to the climate control. I don't know what the function is. Finally, the AJM ecu has a sw/bl changing to white/blue at terminal 20. This appears to be a speedometer related item. The Passat ecu has two white/blue wires, one of which is only used for an additional heater (not for US/CDN), and the other going to the speedo. So I don't know where to connect this wire from C13 on the Passat ecu, or if it is even necessary.
3. sw/gr (Black/grey) going from C15 to the ecu. This appears to match T94/50 on the Passat ecu, same color wire.
4. gn/bl (green/blue) going from A2 to the ecu. This appears to be the engine speed signal. I don't know where this signal is on the Passat ecu, or if it is available there. I would think it would be, but I don't know where. That color wire doesn't appear to exist on the Passat ecu. The Passat climate control has a pin for it, but it doesn't appear to be used on the wiring diagram. I also can't find it on the Passat gauges pinout. They may use the CAN bus on the Passat.
I've got PDFs of the A6 diagrams (and the Passat) if you need them. I'd post them, but there only seems to be a way to post images, not PDFs.
Jon