a/c wiring question
 

I have a 92 fullsize with a 5.3/T56.
I have retrofitted the original a/c system to r134a, and made brackets to use the original-style compressor.
Currently I have nothing connected to the pcm and the a/c is controlled through the in cab thermostatic controls in the dash (I am sure they are called something else).
Under the hood, I have two wires running from the clutch cycling switch on the accumulator both 12 volts. One runs to the compressor clutch, and the other is loose, but was connected to the original pcm that the truck had when it was a 4.3.

I am wanting to connect the one that was originally connected to the pcm to my new (2002 pcm) so the pcm will know when to increase engine rpm when the a/c clutch is engaged (the wire junctions and sends 12v to the compressor, and 12v to the wire that is connected to nothing right now)

Where (what pin) on the new pcm do I need to supply 12v, so the engine rpm will increase when the a/c clutch is engaged?
Also what pin do I need to connect to to signal the electic fan to come on when the a/c compressor is engaged?

Hope this makes sense, thanks for the help.

It doesn't work like that. If you want the PCM to be involved you need to use the pressure sensor and use the PCM to control the compressor clutch.

Another way to put it is that the pressure sensor is used as the input and the PCM is ultimately the decision maker when it comes to turning the compressor on and off. This way you can insure the A/C is truly off when you're at WOT or above a given RPM.

What RPM does the computer turn the A/C off?

Stock I believe it is 6k RPM

On stock 99 SS tune, AC Disable RPM is 4294 rpm, Re-Enable RPM is 3950 rpm. Disable TPS is 100%. Re-Enable TPS is 0%. Dunno what it is in the trucks, but it should be detailed in the service manual and visible in HPTuners/EFIlive.

Thanks guys.
The wire to input that I am speaking of is from the pressure switch. I may not have been clear in the original post.
The rpm cut off, is not really a significant issue for me.

Thanks again.

What is the pcm tuned for. Is it tuned for a truck or a car. If it is tuned with a fbody tune...then you NEED to run a fbody high pressure sensor in the high pressure side of the line. This will monitor system pressures to make sure it is within spec. If you are not using a variable displacement a/c compressor out of a stock fbody...then you need to wire in a cycling switch. A stock fbody DOES NOT cycle. Its all done variably withing the compressor itself. So you wire in the original 1992 fullsize cycling switch into the compressor on wire. Its more complicated than you think to make the pcm control it.

it's doesn't have to be that complicated. The original AC system can stay wired like it originally was, including any cycling switch, except the wire that ran to the compressor clutch now goes to AC Request pin of the PCM. The PCM also connects to a high side pressure switch, and a new (2nd?) AC relay that runs the compressor.

If you try to simplify the system to eliminate having 2 AC relays, that gets more complicated :).

My biggest headache so far has been trying to find a #8 hose to O-ring fitting or #8 hose splicer that has the 10mm switch (sensor) port. I need to give up on that and just get a port welded on. Anyone have suggestions on where to get that done, or someone I can order that from?

Rodder, you have stated that the new VD compressors want work with the older systems. May I ask why? I respect your inputs on here and have gained a tremendous amount of knowledge from you. Bezee states he is running one in his chevelle with original a/c system no issues. I also respect his input and am planning on doing the same but I keep reading it want work. Can you explain why it want? I am not planning on using the pcm for the a/c. I thank my stand alone fuse box will trigger my fan on if I simply route the wire to it then to the pressure switch then to the compressor. This will avoid your issue of having to put a port in for the modern pressure switch. Now that I have located my alt on the passenger side I can't go with the ls1 a/c relocate bracket and change the compressor location.

Yes, you would simply use your original low-pressure A/C pressure switch thats on your trucks accumalator. The A/C wire coming from your dash control is a negative, that you would wire into one side of the pressure switch, while the wire coming out of the pressure switch would connect to your LS computers "A/C Request" input wire. Oops! I see that I just repeated what Rodder said...:emb:

http://www.pro-touring.com/forum/sho...127#post241127

I started with KUL FIR CHICK N wrote above. He works for VA. But I wanted more details, so I did some more research.

http://www.vintageair.com/DownloadsS...ng%20Guide.pdf Vintage Air troubleshooting guide, for description of low side pressures

1999 GM F-body Service Manual for description of V5 low side pressures

Convert the low side pressures to PSIA to figure % reduction in compressor flow for 28psig inlet vs 12psig inlet. I came up with 60% of normal capacity. That may be enough for some systems, not enough for others, and depending on the system you may have an oil flow problem at that flow rate.

I also ran across several people in old threads that said they were using the V5 with other systems, but seeing like 50F evaporator temps.

That was enough detail for me. The V5 will sorta work for some systems.

BTW, VA sells a bracket to bolt a Sanden compressor in the stock LS1 compressor bracket. Or you could fab your own to put something down there--you don't have to run it up top. I'm running mine up top because I don't have subframe clearance for the stock LS1 compressor location.

Thanks rodder. I'm going to go ahead and try it I sense I already have it. I'll only be out the custom hoses that I have to get fabbed. If it turns out to not do the job I'll upgrade latter down the road when I got more of the current swap paid off. Thanks again for your help. The factory one that I had never worked well cause the 330 always ran hot on 100+ days hear in Texas.

These are the fittings I have for the 10mm sensor.

Hot Rod Air in texas has a lot of A/C fittings. Very reasonably priced. www.HotRodAir.com Also... www.ACKits.com Lots more fittings...

F-Body A/C Question...
 

Since we are on the subject, did the 1999 thru 2002 F-body's have an A/C "low-pressure" switch? Where was it located? Was it intregal to the compressor, or...? thanks

they dont have one cause it uses a variable displacement compressor. So it just had a high side sensor. It doesnt cycle at all. its on or off. The VD Compressor does the rest internally

The high side sensor handles all of the inputs to the computer.

The F body sensor is in the high side liquid line on the passenger side of the engine bay.

either of those would work perfectly for me if they were #8 instead of #6!

thanks fella's, always learning more.:thumb: