Ac only works on command

[Duka]

I'm finishing up my Cummins swap into my 2007 2500hd classic, everything is working good so far , the only way I can make the ac come on is command it in hptuners, I'm using a duramax ac compressor and lines "it was a 6.0 gas" no codes from pressure switches, is there anyway I can wire it direct from the factory switches or bypass something to make it work, thanks

[dermotw]

post tune... the ac needs the pressure sensor (not switch) to be there and working.

[Duka]

Here is the tune thanks

[dermotw]

Ok... so you have a pressure sensor fitted and wired? If you have, you can log it and you can log the AC clutch and AC commanded 'on' state. It is all ECU controlled, no easy way to bypass that, imho anyway.

When theres a sensor, the AC will disable if the detected pressure is too high or too low. Your DTCs 530/531 seem to be setup ok...

You could frig the system (if you dont have or cant use a pressure sensor) with a resistor to fool it into thinking pressure was ok, then it should command the clutch on/off... But then theres some risk of e.g. overpressuring it or breaking it somehow etc. I guess...

[Duka]

Ok driving the truck today ac still only works when you command it, battery light has been on since the swap, no idea why it's putting out 14.0 volts and is the original alternator, the battery light went off and the ac works like always, another 10 miles battery light back on ac quits, alternator still charging, checked with volt meter with battery's unhooked, can I turn off the battery light or why is it on thanks for the help

[dermotw]

Hmmm perhaps you have a wiring error, Normally in an LS1 (F-body anyway) the ECU gets a signal from the ALT, called the L-wire... (or is supposed to). If it doesn't see it then it will turn on the battery light (and it should show a DTC as well..).

If the ECU thinks ALT is faulty then quite likely it would turn off AC to save power etc. It might disable a few other things too....

[Duka]

No dtc for alternator , for this truck I don't see a dtc for battery light or alternator in hptuners

[dermotw]

Your tune you uploaded says you use L and also F wire for ALT;

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This is the L-wire DTC anyway... (I don't know trucks or how that system setting is different exactly, except that those 2 ALT wires are enabled in it, sorry);

Capturea.JPG

The only thing I can say for sure (because I have a workshop manual) is that the L-wire is both input to the ECU <and> output from it, and the ECU will flag a fault if it sees wrong conditions there. F or Field wire I don't know what the ECU does with it, because my variant does not use it.