general23cmp

iTrader: (1)

I’m transplanting an 02 truck engine (I believe that is an 411 PCM) into an old truck and will be going with Vintage Air. I’m thinning out my harness, and a obviously there are several input/outputs for the AC to the computer. Which of these should I keep (if I can) to tell the computer the AC is turned on? Also, does anyone know, providing I can tell the PCM that the AC is on, whether the computer automatically turns on the electric fans when it sees this signal? If so, are they on low or high when it does this?

The goal is to have my computer know that AC is on (for idle, etc), and if possible, turn the fans on to help the condenser. That would avoid an additional relay, diode, etc type setup external to computer when the AC is turned on. I know there are also relays required for normal operation.

Thanks.

B52bombardier1

Hello,

Consider the following for simplicity:

https://www.ebay.com/i/274563033540?...AaAkIgEALw_wcB

It is a thermostat for your radiator fans and has a fan kick on wire that turns on a radiator fan the instant that the clutch on your AC compressor turns on. You need that radiator fan on well before it would normally turn on to control AC compressor head pressures from going too high.

I run two e-fans for my radiator and have two of these fan controller kits for best cooling dependability and redundancy. I have adjusted the passenger side fan to turn on at 195 and the drivers side fan at 205. Both of these Four Seasons kits have been running well for going on two years. No need for PCM complexity to control your fans.

There is another manufacturer of kits like these from Australia but I can't find the link right away - more expensive. If you are interested, I will find that link for you.

Rick

general23cmp

iTrader: (1)

Thanks for the advice. That’s certainly an option, but I already have the dual electric fans through the computer almost ready to go. It’s simple and fully adjustable. I’m just looking to see if I can get the aftermarket AC to work with it. I can always go with a simple trinary switch, but didn’t want to have to account for two things triggering fans and the computer not liking the external one somehow.

Andy1

I'm a bit hesitant to reply to you, as it's been several years since I configured my AC, but I'll give it a go. My PCM runs my radiator fans with the GM low/high speed scheme (three relay setup). I run my after market AC with the request through the PCM (for idle bump). I added the GM refrigerant pressure sensor wired to the PCM. Finally, I wired in the GM speed sensor, as it turns off the radiator fans at 40MPH and above (I think).
Hopefully you can glean some useful info from this.
Andy1

general23cmp

iTrader: (1)

Thank you. That’s good info. I’m doing the same with three relays for temperature control. So your GM pressure sensor goes into the computer, and it turns the fans on accordingly? Do you happen to know if the pressure control side puts the fans on high or on low? I’m sure since it’s been some time, you probably don’t recall which of the AC signals/pins you used to input to the computer...correct? I’m glad you mention the speed sensor. I hadn’t considered that, but had been assuming with my computer controlled transmission, that it’d automatically do that for me. Thanks so much. This is exactly the input I need from the team here.

G Atsma

Look up Davies Craig for a controller that has 2 relays to control 2 fans by starting the 2nd fan 10 seconds after the 1st, minimizing the sudden amp load of both starting at once.

67Skylark

I have attached the way I wired the ground form the trinary switch and used the ground from the PMC (E38 in my case). I found the that my two speed fan never needed to run in high speed.. 6.0 (LY6) using the factory car radiator (67 Buick Skylark) I only used two relays, Hope it helps, maybe gives you an idea to cure your issue. It doesn't seem necessary to tell the PMC you have AC, I didn't and can barely tell when the compressor clutch kick in or out the PMC just adjusts to the new load.

Plumber452

I just went through this with my 2005 GMC 5.3, stock PCM and stock A/C compressor into my 1969 Chevy truck. I didn't use Vintage Air but after tons of research, wiring diagrams, etc. the only way the PCM, on the 05, could see the A/C on was through a serial data line going from the 05 HVAC control to the PCM.

What I ultimately did was wire my push button A/C compressor switch to the compressor, through a relay, separated my two electric fans so that one comes on any time the A/C is running, through a relay and everything seems to run fine. I was concerned that without the PCM seeing the A/C running that the engine would bog down at idle when turning on the A/C. The engine idle speed barley stutters when I turn on the A/C. I do have a low pressure switch wired in as well. I reworked the original 05 harness using the information on the LT1 site

Hope this helps

Michael Yount

iTrader: (1)

I have a Classic Auto Air system in mine - no connection at all between the ECU and A/C controls. I run my cooling fans off of a separate variable speed/variable current (PWM) controller. Idle speed not a problem - when clutch engages the DBW throttle picks it up just fine.

ls1nova71

iTrader: (4)

As the others have said, you don't really need it hooked to the PCM. I've been running my cars that way for 20 years without any problems. To do what you're wanting, you would need the 3 wire pressure sensor and it would have to be tuned like an F body for it to work. Just take it easy on yourself and get the trinary switch and wire it to the fan relays. It may set a code if the PCM sees the fan triggered on when it didn't command it, but you can easily turn that code off. Plus, the VA is set up to run a trinary switch, where as if you use the GM 3 wire pressure sensor, you will likely have to have a fitting put in a line to get it to screw into it.

Andy1

I'm running a 01 Fbody computer (Z28, 5.7L). What I recall, is that you need the pressure sensor when using the PCM to control the AC (and fans, idle bump, etc.). The PCM reads AC request, clutch status, and pressure, then responds accordingly. I think the PCM signals high speed for the fans. There used to be a gentleman on the forum that was an ex GM AC specialist and owned an AC shop who explained the whole system to me, but that was 12 years ago. I want to avoid specifics for fear of providing wrongful or misleading information, but please ask if you wish. Good luck.
Andy1

tommy49

Good info for me in this thread! I'm installing the Vintage Air in my 49 and in my research, I never came across the AC system being tied into the pcm.