I've got the AC wired up in my car. I've done tons of research, and I'm pretty sure it's all wired up right but I can't get the damn thing to turn the compressor on.

If I ground pin 43 RED, it will trigger my relay that fires the compressor up. I did that inorder to charge my system with freon, but now that it's charged, it still won't fire the compressor when I send the +12v to pin 17 RED.

On other cars, when the system is bone dry, I can short the 2 leads at the AC pressure switch, at the compressor will come on so I can charge it.

My question is, what lead/leads do I short to trick the LS1 PCM to think it is fully charged? The system is charged now and it blows cold, but only when I manually trigger the relay. I'm just trouble shooting since I'm 99% sure I have it wired up right, the only thing I haven't been able to check is the pressure sensor.

 

What year and application is your wiring harness and PCM from?
What are you using for a pressure switch?
There are at least a few variations of pressure switches used on the LSx motors.

 

Pretty sure engine and PCM is from an 02 Fbody.

I'm using a 3 wire pressure switch I got from autozone for an 02 Camaro.

After I get +12v to pin RED 17, I've got a relay that is wired like so

85 Red 43, DK GRN/WHT, AC clutch control
86 +
87 +
30 Red 18, DK GRN, AC clutch status monitor. This wire also goes to the compressor clutch

That didn't work so I rewired the relay

85 RED 43
86 +
87 RED 18 and compressor clutch
30 +

That's essentally the same wiring, but I was just trying ****.

Please help, I gotta get this car out of here.

 

From an old e-mail:


"I spent a lot of time learning about LS1 AC - I solved this problem in my last Mazda and got it to work perfectly using the LS1 computer. There is one tricky piece that you need but then it is easy. I was surprised at how little info there was about this, even when I called a bunch of hot rod AC places.

The way to do it is to use a stock chevy pressure sensor - ACDELCO Part # 155742 {#22664328} http://www.napaonline.com/MasterPage...ressure+Switch

The hard part is that the pressure sensor needs a "special" port, which I have only found at Docs Blocks, it is their part number AC0146. http://www.docsblocks.com/proddetail.asp?prod=AC0146

That fitting needs to be brazed into the high pressure line - on the Camaro it is pretty close tot he firewall so if it will fit there in the BMW the wires will not have to be extended. Alternatively it can be placed close to the dryer. The other alternative is to use a different drier but that is a lot harder to do because all of the lines have to be changed. If you are having lines made then just have the fitting brazed into place.

Once you have the fitting the wiring is pretty straight forward, there are three other AC wires for the LS1 PCM:

1. AC Request wire needs +12 V INTO the PCM - this is the way that the PCM knows that you want AC

2. AC Clutch wire needs to be used to ground the relay that throws power to the AC clutch - this is the way the PCM turns on the compressor, when it wants the compressor ON it allows this wire to go to ground.

3. AC Status wire needs to be spliced into the +12v that is going to the AC compressor clutch - this is how the PCM knows that when it is asking for the clutch to be in it actually is turned on.


Here are some links to some discussions about this (you have to sort through a lot of nonsense) but the goodies are in there:

http://www.v8rx7forum.com/v8-rx7-non...w-minutes.html

https://ls1tech.com/forums/conversions-swaps/524068-thread-pitch-size-f-body-ac-pressor-sensor.html "


Hope this helps.

 

That's the problem. That's how I have it wired. AC clutch grounds one side of the coil that sends power to the clutch, AC status is tied into the clutch's power wire. When I manually ground the relay, (the AC clutch wire) the compressor will turn on and it's all good. The only problem is that I can't get the PCM to send the ground. That's why I want to deliver a false signal from the pressure sensor in order to verify that the sensor isn't bad or that the wiring isn't bad. If I can deliver a flase signal and the PCM comes on, then I know the sensor or wiring to the sensor is the problem. If not, I have to dig a little deeper.

Thanks

Also, the docsblocks and Napa links you posted are incomplete becaue of the ..... in them. Can you check that for me?

 

I updated the links.

You need to get 12 v into the PCM so that the PCM knows that you want the AC clutch to turn on.

 

The A/C pressure sensor is just that, it sends a varied voltage signal to the PCM that the PCM interprets as to pressure in the system. I'm not sure what the "on" parameter is but if it doesn't see voltage in that specified range, it won't ground the relay to engage the clutch. I don't think you can "trick" it unless you know what it is looking for voltage wise. When the PCM is satisfied that the pressure is high enough.......but not too high......and low enough.....but not too low, it will be happy. That's why you can't just open the circuit or short the circuit to power.

 

Ya, i have that. +12v into pin RED 17 when I push the AC button on the dash.

 

That's what I was afraid of.

 

If you have that than you either the system is too low or too high of a pressure or the switch is bad.

 

In this schematic you can see that it gets a 5 volt reference so that means the PCM is looking for something variable between 0-5 volts which it relates to pressure. I have this working well in my Hot Rod Air system, so I know it works, it's wired exactly like this.

 

An option for the pressure switch fitting is one made by www.owensresearch.com (who sell under the Tubes n' Hoses website): one end -- beadlock crimp for -6 or -8 hose, M10 switch port -- other end for -6 or -8 female oring connection. I installed my GM 3-wire pressure switch on the high pressure side just before the drier (-6 hose size), and are wiring the A/C just like the diagram in the page above

 

yeah, Steve,...........exactly what I did! I got that M10 for the -6 and installed it just before the drier as well. You can also get the inline "T" variety of that as well. Thanks for that, I was looking for that fitting piece in my notes to add to this conversation.

 

It's a brand new sensor and the system has got 1 can of oil and one can of freon in an FC. Seems low because last time I had my air working (w/o PCM control) it took 1 can of oil and 2 cans of freon. It blows ice cold now, so I didn't want to over charge it. Even if it was a little low, I think there should be enough in there to trigger the compressor to cycle on. Even if it cycled on and off again.

I'll try to cram another can in there.

 

Ok, wtf....

I went outside, hooked up my AC manifolds to the low pressure line and opened up the freon. A little bit went into the system. I cranked the car, and the damn compressor comes on. So I charge it for another few minutes and it's all good under the hood.

 

You were just under the minimum pressure

 

My system requires 1.75 lb of R-134A, that might be close to three small cans I suppose, I filled mine at the shop from our 30 pounder on the A/C service cart. You were probably just under a bit. Great!! Now you are workin'!

 

Tubes n Hoses (Owens Research) wouldn't sell directly to me, and referred me to a local dealer. I ended up getting my M10 fitting done by Wizard Automovie in Douglasville, GA. They're about 30 miles away so it was cheaper for me to UPS the hoses to him & back than to drive over there. I sent him my Vintage Air hoses cut/marked and ready to be crimped, and he welded an M10 port onto my discharge hose's fitting and crimped both lines. I think it cost me about $30 + shipping for the welding and crimping.

 

anyone have a source for the plug that goes into sensor. Does this come off pcm harness?
thanks.

 

It's on the PCM harness, less than a foot from the PCM on my '99 F-body harness. Mine has 3 wires--purple, red, and gray. Those colors match the PCM wiring diagram in the PCM section of the factory shop manual, but DO NOT match the AC wiring diagram in the AC chapter. I noticed a couple of other errors in the wiring diagrams in the AC chapter too--stick to the PCM diagrams.