A/C and ECM/Computer

[CumminsBronco]

A little background info. I have a 1997 Suburban that I swapped a 5.9 Cummins into. Without the gas engine I no longer needed many of the electrical circuits to the ECM. I thought I left all the circuits that I would need for the air cond. to work. Apparently I was wrong. So, in addition to all the circuits that are shown on the Air Conditioning/climate control schematics, what else might the ecm be looking for in order for the AC to work?
For example...does the ecm still need a crank position signal? Others?
Thanks for any info you guys might offer.

 

[Schurkey]

Are you sure the computer is the problem, and not something inherent in the A/C system?

Maybe the compressor doesn't engage because it's low on refrigerant.

Or there's a popped fuse.

Or the control head in the cab is defective.

 

[yevgenievich]

Ecu has functions to shut off ac based on engine speed as well I believe. Might be easier to rewire ac system as an older setup using high and low switches in series from request to the relay

 

[CumminsBronco]

Are you sure the computer is the problem, and not something inherent in the A/C system?

Maybe the compressor doesn't engage because it's low on refrigerant.

Or there's a popped fuse.

Or the control head in the cab is defective.

Schurkey, all fuses checked and are good. The dash module as far as I can tell is OK. After installing the new compressor, condensor, accumulator, lines and orifice tube, I pulled a vacuum down to 250 micron. Held overnight. I did the initial charge if the system, then had to hook batt power straight to the clutch to finish the charge. Gauge readings look good. Still, not getting a signal at the comp clutch relay in the underwood fuse/relay box. I am getting batt voltage from the light green wire when the AC button is pushed on the dash module. I'm stumped and have to assume that the ecm is looking for other signals/inputs besides just what is on the AC schematic.

 

[Komet]

Are we talking about this circuit?

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If you're getting +12v at LT GRN going into the A/C Pressure Cycling Switch but never +12v on DK GRN coming out, your switch might be bad. Temporarily jumper LT GRN to DK GRN and see if your compressor kicks in.