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Right.  That's confusing; seems like it is routed incorrectly.   Worked perfectly fine yesterday.  Even more confusing.

Yep....that's what I was going to do until I ran into a couple of hurdles.....no supplier on this side of the border had the aluminum crimps available, no supplier on ebay in the states at that time who had them would ship across the border, no shop in the nearby area had the equipment to fabricate custom a.c lines.  Go figure

Since this has turned out to be more complicated than I initially thought, I think I'm going to just go with custom made AC lines. I can use both stock 92 Cutlass lines from the evaporator, the drier, and condenser. Then all I need is to cut and splice the Impala compressor-end hoses to the Cutlass condenser+drier ends. Two hoses, 4 crimps, no problem!

I had a fun chat with ChatGPT and learned some possible solutions. One is to just use an aftermarket pressure switch, wired inbetween the Cutlass HVAC module AC Rquest and clutch relay. Another option is an 02-03 GTP PCM (also 00-02 Regal GS and 02-03 Bonne SSEi are potentials). It's an L67 with an 4T65-EHD, plus is has a discrete AC Signal request input instead of a Class2 signal from a BCM. I'll just have to repin a few wires at the PCM connectors. The GTP is probably a great choice because it has full support in HP Tuners, which I already own. The 04 Impala PCM is supported in HPTuners also but I don't think it supports all features.

I'm definitely not looking to go with a manual switch. Let me see if I understand how the system works in the 04 Impala... The HVAC Control Module has an AC Request Switch, when driver wants the AC on, it outputs a Class 2 Serial signal to the BCM. The BCM doesn't appear to have any other direct inputs related to the system, so it might just pass that along to the PCM. The manual does specifically state that the AC Request signal comes from the BCM, not from the HVAC module. In any case, the PCM needs a Class 2 Serial input containing the AC Request On signal. Then the PCM decides along with the other inputs if it should engage the clutch. If it doesn't get this signal, the PCM will never trigger the clutch relay to engage. So if that's all correct, I think I have three options. 1) Find out if there's a PCM that will run the L67 but doesn't use a Class II signal for the AC Request Signal. 2) Simulate a Class II Serial signal with an Arduino including an AC Request On message. Other forums have decoded the signals, further research is needed to determine if this is feasible. 3) Bypass the PCM entirely, again with an Arduino. Take the AC Request signal from the Cutlass HVAC module (which I think is actually just 12v switched?), the AC Pressure Switch, optionally Power Steering pressure switch, throttle position, and coolant temp sensors, all into an Arduino programmed to power the clutch relay under the right conditions. None of these options sound fun! What is different about my swap that makes this neccessary? Tons of people have put 3800's in W-bodies and I've not seen anyone talking about AC issues.