Hello everyone,

This is somewhat complicated to explain and I hope that someone can help me out.

I have a 1990 C4 that originally had the L98 in it. I swapped it out for an LS3 last year. Everything in the car functions perfectly except that I can't get my electronic climate control to engage the A/C clutch without the L98 ECM.

I have the original L98 ECM in the rear compartment of my trunk and it currently has power, ground, and the two tan serial data wires connected to it. I did this to keep the CCM/BCM from throwing a serial data code.

As one can see on the second page of the A/C Clutch diagram, I am planning on connecting the A/C Request wire to pin R15 on the L98 ECM and the A/C Clutch Relay ground wire to pin Y13 on the L98 ECM like factory. I am assuming that the ECM won't ground the clutch relay unless the engine is running. Is there anyway of tricking the ECM into thinking that an L98 is running?

Does anyone have a better idea on how to do this?

Thanks in advance to all that can help me. (BTW I do own a third gen!)

 

couple of options here....

555 on the EST wire that starts generating pulses whenever the ignition is turned on will get the ECM thinking the engine is runnning.

there are probably simpler ways though.

 

The LS3 ECM doesn't have outputs you need? Sarr is saying it has to run as well, not just be turned on? If it has to run you could run a wire from LS3 ECM to old ECM from an ignition source to cause DRPs would be all it needs, maybe... I think it would work just turned on though.