Re: Stock air conditioning with LS swap
 

So your sensor controls the fans, but doesn't cause the compressor to turn on or off?

Can you explain what you mean by a pressure fault? TIA

Re: Stock air conditioning with LS swap
 

I know I'm not TR65, but it sounds like my A/C setup (wiring/PCM wise) is pretty much the same as his. I have a factory 05' (Sierra Denali) pressure transducer in my compressor discharge line. Like TR65 mentioned, it controls only the fans, since you need a serial request for the computer to control the compressor. The PCM will still see the pressure in the system and run the fans without the A/C request signal.

As far as the pressure fault goes, there is a high/low pressure protection system built into the PCM. If the A/C pressure goes too high or too low (low is normal, just cycling the compressor on/off to prevent freezing the evap), the PCM will turn off the compressor. It will also cut off the compressor with WOT. Since we lose PCM control of this, you would need a low pressure and high pressure switch in the system, wired in series, to cut off the compressor in these situations. In my case, I used the factory low pressure switch (88' squarebody crewcab), and my replacement Denso 10S17F had a high pressure switch in the back of the compressor body (which cuts out at 455psi). So, I have 12v from the factory control head, through the low pressure switch, through the high pressure switch, to my relay, which controls the 12v+ side for the compressor. If any of the switches goes open, my compressor shuts off.

Re: Stock air conditioning with LS swap
 

Thanks for the info. Does your compressor come on and stay on until you turn it off? Mine isn't it's cycling on and off and I assume it is being controlled by the computer, which would lead me to believe that it has some over/under pressure protection that is being provided by the PCM. But I would like to be certain because I don't want to damage anything. Thanks again. FYI, I'm using a 2006 Tahoe P59 PCM. More info here: http://67-72chevytrucks.com/vboard/s...=709611&page=2

Re: Stock air conditioning with LS swap
 

Yeah, mine will cycle due to to the low pressure switch being in series with the signal to the A/C clutch relay. When the pressure gets too low, it goes open to cut off the compressor, and prevent the evaporator from freezing up.

To confirm how yours is controlled, you'd need to trace the wiring. If the trigger wire to the relay is coming from the PCM, the PCM is controlling the cycling. For a 2006 PCM to do so, I believe it would need to have a serial A/C request in most cases. I have heard of a few cases where people were able to get the later PCM to accept a 12v+ A/C request, but in talking to a few tuners and harness builders, it was hit or miss on success.

If the trigger wire is coming from the low pressure switch on the accumulator (assuming you have one, and aren't using a POA valve system), the cycling will likely be controlled by that switch.

Re: Stock air conditioning with LS swap
 

Here's how my system is setup:

My setup:
3 wire truck pressure transducer connected to plug from Speartech harness
12volt a/c signal from the VintageAir to Speartech harness green a/c request wire
Two wire (green and black) plug to factory 2005 compressor from Speartech harness
NO binary switch (in dryer not wired)
Blue/Green PCM OS 12587811 & system 12591524
Compressor type - ANALOG

Re: Stock air conditioning with LS swap
 

Definitely sounds like the PCM is controlling it, in that case. That's really the best way to do it, as you'll have WOT compressor cut off, high pressure cut off, etc.

can you take a few pictures and tell me where you got your hoses built or part numbers?
Posted via Mobile Device