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two thoughts:
the first I have done successfully, the second just an idea
1) on my Toyota Land Cruiser (I know, I know, but I live in rural costa rica, a metro would be a zero mpg vehicle for me) there is an auxiliary fan on the front that runs when the AC is running, to help cool the condenser up front. Toyota includes a "medium" pressure switch on the AC system that is normally open, but closes when the pressure is above a given level. I don't have the number handy, but it is at the middle of the AC pressure spectrum. In any event, tapping the fan control relay into this switch means that instead of cycling the fan w/ the compressor or the AC-on button, now the fan turns on when the pressure in the condenser builds up, and turns off when the condenser is cooler/lower pressure. I don't think that this saves an awful lot of energy-- but it does mean that the compressor seems to cycle less often, which saves some energy, and that the fan only runs when needed (ie: at higher speeds the airflow is sufficient to cool the condenser and the fan doesn't run).
2) Here's the mod I haven't tried (yet) but plan to do-- my A/C blows cold. Very cold. Colder than I want. On LOW in the evening I get uncomfortable. I don't want to adjust the temp in the cab as that just puts engine heat in to fight the cooling and is wasteful. So I'm looking at adding some sort of system in to fool the system into shutting down the compressor with a little less pressure in the system. I think that putting in a switch and a resistor should give me the option of "low setting" on the AC. Or adding a potentiometer can make the level of coldness variable. Anyone who knows more than I do about how the thermistors and pressure sensors work... please pipe in!
Thanks
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