k5383

iTrader: (10)

Im in the midst of putting a lq4 into a mid 80s chevy truck. Would love to run the a/c off my head im not sure how the ECM controls the clutch on the compressor though...

Scenario one: ECM solely controls turning on the 2nd e-fan (if equipped) and when it drops the idle, the computer will automatically compensate. No actually wiring from the compressor/hi-lo switches/etc.

Scenario 2: ECM controls e-fan, on/off clutch cycle, and it "knows" to bump idle, not to compensate for the drop.

Scenario 3: knows to bump idle, control fans, but does not control clutch cycling.

Im hoping its scenario 1... if that's the case, any reason I can't use my factory wiring (with new pigtails of course) and ride out?

I've already finished the harness... if need be I can unloom it all, not a thing I want to do, but if im required to re-pin the ECM plugs then so be it.

Thoughts? Anyone done a 80s truck swap with a/c and some tips??

Thanks fellas...

mantycarguy

Scenario 2 is most correct.The pcm controls ac relay and fan relay(s). The pcm adjusts the idle speed just prior to ac clutch engagement to compensate for anticipated idle drop. Many people have successfully deleted a/c controls from the pcm and have had little or no problems. The pcm stll monitors idle speed and will see a drop during a/c engagement. It will then adjust the speed up to the proper rpms. This can cause a slight surge and under the right conditions a stall.

k5383

iTrader: (10)

Hhmm, so the fact that this will be cammed and is a stick could cause problems...

Guess I need to study the schematics and go back over some stuff...

Thanks for the reply..

Any other opinions?

garys 68

iTrader: (1)

In order to have the ecu control those functions, it needs to monitor the refridgerant pressure. Those can be transferred from the original vehicle.
I'm running an LQ9 and LM7 with aftermarket AC systems and manual trans, no problems.

k5383

iTrader: (10)

That makes sense, however my desire is to avoid that. If at all possible id like to re-use the "old" system

chuckd71

iTrader: (23)

Cool info.


Edit - pun not intended. Had been wondering same thing.