Hello everyone this is my first post here. Firstly I'd like to thank everyone who contributes to these forums. They've been very helpful in getting our 81 Firebird ls swap done.

Anyways Ive been digging and digging in all kinds of forums looking for some info.

We got a 81 Firebird with a 5.3 out of an 04 Tahoe. Got a 03 Express van ecu to run a cable throttle body. The car runs great, fans are wired up and kick on and off as they should.

Now Im wiring up the ac. I got a 12v signal wire running from the factory 81 firebirds hvac switch panel. It DOES NOT go through a high pressure switch (probably not smart I know) and goes straight to the ecu.

We are using the stock junction block so pin 43 on c2 goes to the junction block. I got a low pressure switch wired up half ***, one wire goes from pin 55 on c2 I beleive. To the low pressure switch, the other wire I have tried grounding it (this sends a ground back to pin 55 c2) as well as give it power (this gives 12v back to pin 55 c2). Neither way allows the ecu to send the ac command signal (ground from pin 43) it stays on 12v no matter what.

so my basic question here is

a) does pin 17 NEED a high pressure switch before it goes to the ecu? does it look for a specific voltage or ohms that is not a standard 12v?

b) what voltage or ohms needs to be sent to pin 55 c2 for the low pressure switch?

I have the schemtaic for the 03 express van. It shows there to be a hgih rpessure switch inline with the ac request signal. It also shows the low pressure switch to go from pin 55 c2, through the low pressure switch, then to the AC compressor, as well as a ground. It looks like the same wire.

To shake things up a bit, we are not using the stock 03 compressor. I have a Sanden SD5 (i beleive) It is a one wire compressor. There is only one 12v clutch wire on it.

Any help is much appreciated!!!

 

You dont necessarily need the high pressure switch, but I would recommend it as a good amount of protection in the system. As for the low switch, it is just in line to ground, and not the compressor itself. Just ground the compressor and run the power from the A/C relay to the power to the clutch.

 

Thanks for the input Nova. Ive seen you comment on multiple threads I was reading into.

Okay so, I got the compressor's power and ground set up. I grounded pin b on the low pressure switch with the pin a wire going to pin 55.

So I can commend the relay to kick on with a scanner while the key is on, but engine off.

With the engine running, it says cannot command ac because ac pressure out of range.

Ive charged the system a bit just to get above the low pressure but it still does not kick on. Then I charged it more and more until I felt like it was probably too full but still would not kick on.

 

So I think I might have a big mix up going on. I got an 03 express van ecu. My wiring diagram shows that it has a low side and high side switch. However the 03 truck ecu has the trinary switch setup. Is it possible that this particular ecu was supposed to have a trinary switch?? Everything else in the ecu has been wired up as an express van ecu and works fine that way.

 

So you have a van tune, but are you sure it's a van PCM and not a truck one? What's the service number on it?

 

What are you using for a scanner and are you doing the tuning? Just a curiosity thing. Can you use your scanner to check the ac pressure? I was using tech 2 and even when I switched the pcm to analog cycling it was still looking for the pressure sensor. Sounds like your having a similar issue. If your doing the tuning try making sure the ac is set to analog cycling and the platform code is set for a van. In then end even after I did that I never was able to get my ac working without the pressure sensor

 

OK your post is a bit confusing. First off GM never used a trinary switch on any new vehicle if it is 3 wires it is a pressure sensor. Regardless try this:
1. AC request put 12 volts to it. Pin 17
2. C2-55 ground it.
3. Pin 43 should then go to the relay and turn on the compressor.

You should be able to log the ac request being on. If not it is not receiving the ac request. This would be a PCM issue where you programmed the PCM to the van OS but it does not have the proper drivers.

If the compressor goes on for 1 sec then off check for code P530 and turn that off.

If it doesn't come on at all it is on the back end on the compressor side not the PCM.

 

Thanks for the input everyone,

Nova- The hdw no. is 12570558 and the serv no is 12576106
Im not 100% sure if it is a truck or van ecu. However I thought they were the same a/c wiring schematic.

GBody- I am using a Altec Maxis Pro. It is a very good scanner for the price. I can check lots of things with it however In the section dedicated to "heating and air condition" the scanner refuses to connect. I think it is looking for something from a body control module or something. Under generic functions I can see lots of data but not the actual a/c pressure unfortunately. I DO see however, that it does acknowledge when the a/c request comes on. So it is receiving ac command to come on.

Im about to see about the ac analog cycling setup that is in HP Tuners correct? That is what Im using and yes Ive been playing with the HP tuners myself. Have gotten the car running, fans working, and thats about it. Got a million codes for transmission things. Thatll be the next challenge Im sure.

69 Ghost- I got ac request hooked up to pin 17, c2-55 grounded,

no ground signal sent from 43.
The compressor is hooked up correctly I beleive because I can command the ac compressor on with the scanner when the engine is not running.


PAUSE; Timeout...

I just looked up the service number and it looks like its an 03 Truck ecu....

03 truck ecu uses the Pressure Sensor and not Switches...

can someone verify this some way some how? The service number that is. If thats what I got then I need to make a new ac line and rewire some thangs >(

 

Turn off P530

 

That PCM has IAC drivers so you're good to go there, it should accept the van tune and the 12v A/C request, just make sure its set to analog cycling.

 

The pcm that I had tried to switch the ac request on is the 6106 hardware number. I was never able to switch it to the high and low pressure express van setup. It would only recognize the pressure sensor input so I ended up faking a pressure sensor signal.