Most of the older A/C systems in GM cars do not have a high pressure switch. After doing some reading it looks like the 70 chevelles may use a POA valve and do not have a low pressure switch either. I haven`t messed with one of those systems before. Do you have any pics of your a/c lines and evaporator core?

 

Yes the Chevell's A/C control wire would go to the high pressure switch and then to the PCM, the high pressure switch is mounted on the back of the '99-'02 compressors. The low pressure switch is generally mounted on the accumulator right outside of the A/C box on newer cars. Your Chevelle doesnt have high or low pressure switches, it originally would have had a blow off valve on the compressor so if the pressure got too high, it would just blow it out. They also didn't have any low pressure switch, because the compressor ran continously, and the POA valve adjusted the flow of freon. The old system worked great, when they worked, but once they start giving you problems, it was party over. You haven't been able to buy a good POA for years, and they were spendy when you could. I like to think of the POA valve as a distant cousin to the carburetor, one day they work perfect, and the next, not so much, and the next day maybe fine again! Can you tell I don't like carbs?

That all said, if you want to keep the A/C, and only want to do it once, do what you did to the original Chevelle engine with carb, and throw it aside and get some newer technology. What I would suggest is getting an evaporator out of a newer car with an orifice tube and accumulator and putting it in your original A/C box. Another member on here that i know who has a '71 Chevelle, said he put one out of a late 80's or early 90's Camaro in his, so that will give you something to look into. From there you would just have to have some lines made to hook everything together. This way you would eliminate all the old parts that usually go bad and keep the A/C from working. I'm sure you're on a tight budget and don't want to hear that you need to buy more parts, but I think in the long run it would be in your best interest, and will keep you from throwing good money after bad.

And ask all the questions you need, it's the only way you learn. When you get it all figured out, and you're driving around in the comfort of an A/C equipped Chevelle, you'll have the satisfaction of knowing you made it happen!

 

This is what I'm currently working on. It's a '71 Chevy truck with an evaporator out of an '87 Chevy truck. Just to give you an idea of what it would look like. Edit: In the 3rd pic, the fitting between the two lines, is where the low pressure switch goes. I need to get a new one, so that's why it's not there.

 

Using a newer setup definitely sounds like the way to go. What should I look for in the donor car setup? I guess it will need the low pressure switch somewhere. The local salvage yard says they have two 1994 v6 camaros. Would that be a good system to use?

 

What fan shroud are you running on that 71 chevy truck?

 

I'm not sure about 4th gen Camaros, you would need to take your original evaporator out, and find one that is close in size and shape, with the lines coming out in the same basic place. The next time I'm at the salvage yard, I'll look at a 4th gen and see if I can tell, and I'll get back to you. I'm pretty sure a 3rd gen one would be a close fit though.

 

It's a stock 67-72 Chevy truck with a small block shroud.

 

I just got back from the salvage yard and they have quite a few third gen Camaros too. That setup looks like it will fit better but it is intended for R12. Is there anything that needs to be converted to work with 134a? In the swaps that you have shown me have have you used the factory AC lines or did you have to get custom ones made?

 

Yes there are things that need to be done to convert to 134a, you'll need to flush the evaporator really good to get all of the old mineral oil out, and you need to find the biggest R134a condenser that you can fit in the car. I wouldn't try to use a used one, because you cannot really flush them out, and having a good condenser is a must, it's basically what takes the heat out of the system. Depending on your budget, it may be in your best interest to buy a new evaporator as well, just because they are a royal pain to change in a fully assembled car if it were to leak, and it will be your only used part, with the exception of the compressor. I usually get one from a pick a part, and use it for mock up then once I know it will fit I'll get a new one. I wouldn't say it was mandatory though. You will however need a new accumulator and orifice tube.

The lines on my '72 (the blue one with the build thread in my sig) were all stock 2003 Silverado, but I did bend one coming off the compressor and in the process broke it, so I had it welded at a slight angle. On the orange '71, the lines are a mix of stock lines that have been TIG welded together, and fittings from the auto parts store with hoses crimped on them. By TIG welding the lines, you can go to the junk yard and pull some aluminum A/C lines and fit them together to make them go where ever you want them. You can also weld barb fittings to the end of a factory line so you can crimp a hose on the end if you need to. On my orange truck, the big line coming out of the accumulator on the the passenger side is part of the original line that has had a barb fitting welded on and a hose crimped on it. I should mention that I don't have a TIG welder, but I know a guy that's very good at it, and I just take them to him after I get them cut and fitted where I need them.

 

Do the accumulator and orifice tube have to come from a 134a car? I guess I will just have to look around for hoses that will fit. Would the third gen's evaporator have metric threads that fit a 2001 Silverado hose?

 

No, the accumulator and orifice tube don't have to come from a 134a system, just use the parts that match the evaporator you use.

As for the lines, the 3rd gen Camaro and the 2001 Silverado use two different type of fittings, so some custom lines are going to be necessary. Do you have the factory lines off of the 2001? If not, then you will need some to hook to the compressor to fab your lines off of, or you might try http://www.docsblocks.com/, as they make fittings to bolt to the compressor, then you can get a hose made up with fittings to hook to them, and your accumulator and condenser.

I hope this is clear, I know what I'm trying to say, so it makes sense to me, but may be a bunch of mumbling to you if you don't understand. If it doesn't make sense to you, let me know and I'll try and clear it up a bit.

 

I'm watching this too as I have a 72 GMC with a 2001 6.0 in it, and will be installing the Ls compressor to the original truck a/c components. Good info guys.

 

I understand what you are saying. I just need to figure out what hoses I am going to use. Hopefully the Silverado ones that come off of the compressor will be long enough to reach. That way I can have different fittings welded on or maybe even find adapters to connect the different fittings.

Thanks again for all of the help,
David

 

I'm kind of bringing up an older horse here but I'm looking to wire in my vintage air system with the 2002 Camaro computer. I just want to make sure I've got this correct.

Pin 17 (AC Request) comes from the unit inside.
Pin 14 (AC Refrig Press Sen Sig) Not used as I am using a Sanden Compressor with no High side switch?
Pin 18 (AC Clutch Status) where does this come from?
Pin 44 (AC Clutch Rly Control) this runs to the relay to kick on the compressor.

Also, am I correct that the factory computer cuts the compressor above a certain RPM or 100%TPS? I'm having a problem with long WOT runs and the low side going too low. The system runs fine other then that. Freon levels are fine and the system cools really well.

 

If you guys are using a variable compressor you should have the pressure switch. This is the variables equivalent of a hi/low switch and it also controls the fans. If you are using a fixed compressor you need the hi/low switch both types can and should be controled through the PCM. Either way you can wire it according to a 02 truck or car respectively and turn the a/c on with the a/c request which is 12 volts and can be wired directly to the original a/c switch. The PCM then needs to have the a/c type set to the proper a/c type. Even a GTO PCM and OS will work this way and turn on the fans accordingly which is not what most people say because the wiring does not show it but the newer 1mb OS's are essentially the same as the 02 Camaro/Vette/Truck 411's and interchange accordingly. Both the a/c and the fan can be controlled by the PCM even though the GTO's controlled the a/c and one fan through the BCM.

For the oriface valve all you need to do is match the type to a 134 and they are cheap about $20. I have not run a POA but it was recommended by a A/C guy in Arizona to change it out for a oriface valve. If you use an old system like a 3rd gen then again you need to replace the oriface valve to the proper type. For the vintage air or similiar conversions the system uses an expansion valve which acts essentially the same as a oriface valve and it regulates the flow of 134. Vintage says a variable will not work and burn up the compressor and Classic Auto Air says it will work. I have run both a GM R4 and a Sanden on the vintage setup and found the GM unit actually worked better. I now have the variable compressor on my car but have not run it enough to give a verdict as to the efficiency for a yea or nay. If it is not good enough I will convert it to a fixed compressor and there is thread that explains how to perform this.

When you convert the a/c you should strongly consider changing the condensor. The older R12 condensors will work but will not be as efficient. Apparently the 134's generate more heat and I believe they also use bigger tubes and area for more heat rejection.

If you guys have an original A/C setup in your car do not be tempted to go to aftermarket unit make the old system work by combining it to a newer system. The control of the factory systems is sooooooo much better than the aftermarket systems.

Look at ls1nova's truck build thread. Not only is that a beautiful truck he did the a/c right with a factory setup.

 

I know this is a old thread but thought one of you would have a answer for me. I'm getting ready to do a ls swap on a 72 skylark, and will the compressor fit in the stock location low on the pass side of the block or will it his the crossmember in the car?

 

I believe if you use the Holley forward mounts, they have a bracket that will let you use a Sanden compressor down low on the passenger side without notching the frame.

Andrew

 

If you use the Forward Holley mounts, the stock compressor will fit with the stock brackets if using a truck set up...