In a conversation with @Shoreguy in another thread I learned that the AC compressor was cycling in more modes than AC and defrost. That bugged me because I don't particularly like AC, and don't want the hit on mileage. I'd rather turn it on when I want it on. So I looked at the diagrams and found a variety things, but showing that it was active in more positions than AC and defrost which was what I had assumed.

The wiring diagrams are likely correct in terms of point-to-point wiring, but what is shown withing the boxes representing switches and other devices is best considered an artistic rendering. It's not always useful for troubleshooting. Mine is a 2004, and I have diagrams for 2002, 2005 and 2008. The 2002 and 2005 don't show the floor/vent position at all and the 2008 shows the AC engaged for all modes but "off". So I pulled mine apart.

On my 2004 the AC clutch is energized for both AC and DEFROST modes, as well as FLOOR/VENT. It is off for FLOOR and VENT, as well as OFF. I thought about disabling the AC for the FLOOR/DEFROST mode but decided to leave that alone, and just disabled it on the FLOOR/VENT mode. Taking the HVAC unit out was pretty easy, but taking the mode control out is not for the faint of heart. Note the detent spring and ball behind it that can easily get lost. Also, there is a sliding vacuum control valve moved by the gear, and that must be phased properly on reassembly.

To disable the AC on FLOOR/VENT I cleaned off that one spar with brake clean and applied some thin Kapton tape over it. That is a tough resistive tape with a good adhesive used in electronics manufacturing, which was suitable for this, but there are probably other tapes or ways to insulate it. Now when the wiper hits that spot it will not make contact and the AC won't turn on. I reapplied some silicone grease and put it back together - had to replace a bulb too. Everything worked well. Since I use FLOOR/VENT and FLOOR most often I'm hoping I may see some mileage improvement.

 

Nice write up and pictures

And good idea to coat electrical contact to prevent a circuit in selected positions

 

Thanks! I'd so much rather have a system where I can control the temperature, the fan and the outlets, and a separate button to turn on the AC. I guess that's too hard for people, and they don't know that the AC reduces humidity, so it must be done for them.