not exactly a tuning question but also interesting :
Here's the story
After a looong weekend with lots of trouble I finally got the AC compressor in my Tahoe.
I also installed the modified hoses and created a temporary wiring harness to run the 2007 compressor (internal variable displacement type out of 2007 6 cylinder truck) with the 1997 HVAC unit. I used the AC request signal ( I had to change the polarity to active low..) and wired it through the cycling pressure switch in the receiver drier.
This pressure switch, when closed, switches the low AC request signal to the engine fuse box where the compressor relais is switched on.
The 2nd pressure sensor is driving the recirculation motor when the pressure in the AC system raises above a certain value.
Ok now the interesting stuff:
I am wondering how to set the fans when the AC is switched on. I use the 2007 OEM dual electric fans. They have two speeds, slow when switched in series and fast when switched parallel.
Compared to the 5.7 mechanical fan I guess the slow setting draws more air through the radiator than the old system. For my personal feeling the high or fast setting is a little overkill.
Does anybody have more specific idieas about the fans settings I should use?
Then, when I looked at the 2007 Chevy Tahoe AC schematics I thought about the following: What would the E38 do if there was no AC request signal on the CAN bus, but the hard wired AC pressure sensor ( three wire type, GND, 5Vref and output) is getting high pressure readings? Would the E38 switch on the fans??? Maybe our EFI Gurus could trick the ECM in that way that it watches the AC pressure sensor and switches the fans according to pressure in the system.
I could also imagine to use the compressor clutch output of the E38 for additional safety in the above wiring. I could use the simple wiring for switching on the AC but I could also check if the E38 tries to switch off the clutch because of high engine rpm or high AC system pressure...
Harald
more info and pics on :
http://www.pacificp.com/forum/viewto...?p=73860#73860
