Quoting GSTwithPSI:
Chris,
The wire going to pin 65 is grounded by the ECU through IC109. IC109 is activated with the key in the ON position and the engine running/cranking. This driver also controls the fuel pump via the MFI relay (pin 56), so chances are, if you're fuel pump is working as it should be the driver is functioning properly. You could pull the ECU and do a visual inspection to verify. You can use this thread to assist you:
click . It will be the driver closest to the edge of the circuit board. Check it for any sign of damage.
If you run a wire from pin 65 to ground, you'll basically be activating the compressor relay at all times so long as the dual pressure switch is in its operational window and it's receiving power (need to see the other side of the diagram to determine when it's receiving power). The wire going to pin 65 basically gives the ECU the ability to control the A/C under certain conditions. I'm not clear on the exact logic, but I believe the ECU will shut off the A/C under WOT conditions, and also if it sees the car overheat (unsure of exact temperature). If you ground the wire going to pin 65, you remove the ECU's ability to control the A/C. Just FYI, pin 7 (A/C coolant temp switch input) tells the ECU to bump the idle when the A/C is on, so you can verify this is working just by observing how the car behaves with the compressor on.
I'd need to see the other side of the diagram to tell how grounding pin 65 would affect the system overall (where wires 1, 2 and 3 go pictured upper top left hand corner). As long as the dual pressure switch only sees power with the compressor control unit activated, I'd think you would be fine grounding pin 65. For the most part, the wire going to pin 65 should go to ground the majority of the time with the vehicle on and running anyways.
GST, thanks so much for this info. At first I was afraid that if I simply grounded that one wire that my compressor's clutch would constantly be on and the ac would never cycle as it should. Like I said, I ran a simple test yesterday and let the car run for 10-15 min and it cycled off and on normally. Also for some reason the schematics show that once power comes in from the LR (light blue/red) wire, pin #3 on connector A-24 that it should send power to pin 1, the yellow wire. In my case this was not happening and that yellow wire never saw power. Once I grounded that black/white wire (pin #4) it worked as it should and the yellow wire saw power once the ac was switched on.
I see what you're saying about the AC shutting down if the car overheats or under WOT. This is my DD and it never sees WOT and I always keep an eye on my gauges so I think I'll be good there. Honestly, its hot and humid as hell here every day in the summer here in NC so I just want the AC blowing cold at this time. I plan to re-visit it this fall when I can comfortably work on it and maybe see what I have wrong. For now if grounding that wire will safely make my AC work, that's what I'm going to do. I will still scan the other pages of the wiring schematics for you guys to take a look at. Maybe fresh eyes will see something I don't. I don't know about you guys but I can only concentrate on wiring for an hour or so at a time and it all starts to look the same after that and I get frustrated.
