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1979 El Camino (yellow), 1979 El Camino (blue)
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Discussion Starter · #1 ·
It's getting hot! Time to get the AC working on my 1979, which has a 5.3 from a 2000 Silverado. It has the original G-body evaporator, plus a low-mount compressor on the 5.3 engine, plus a new 4th gen F-body condenser. I also have the original high pressure line that goes to the evaporator, and the discharge line from the Silverado. I've cut those up and combined them with new fittings and hoses. I'll use a new compressor, accumulator, and orifice tube, and I'll flush the evaporator.

I've used the coldhose.com website, and have made several orders for fittings and hoses. I've got my hoses mocked up, and will take them to the local hose shop to have them crimped. But before I do that I've got questions.

Here's the design I've come up with. Below are the questions I can't figure out. Any help would be great.
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What low pressure switch? For the low pressure switch I want to use one of the two Schrader fittings on the accumulator. I'll use the other one for the low-side port. But which switch? Will this Four Seasons 37308 for a Cadillac Escalade work? (Amazon.com: Four Seasons 37308 System Mounted Cycling Pressure Switch: Automotive) Will it fit a male Schrader valve? It is for R134-a.I guess if it works I can get the matching Escalade electrical connector. Or is there another switch that's a better match?

Do I use the high pressure switch on the compressor? This unfinished swap came with a discharge hose, which I think is from the Silverado engine. The discharge hose has a high pressure switch in it, which I plan to use. But the compressor also has a pressure switch on the rear. I've read a little about it being some kind of auxiliary switch. Do I need to use it?

How to wire the high and low pressure switches? I will connect the AC request wire from the G-body to the request line on the Silverado PCM. This tells the PCM that the compressor should be on, so it can raise the idle and turn the fans on, and whatever else it wants to do to compensate for the load. The PCM has a compressor out wire that will go to a relay to send power to the compressor. Do I just run that compressor out wire through both the high and low switches so that if either pressure switch is open the relay won't close even when the PCM is wants it closed? Or something similar where the control side of the relay doesn't have a ground if either switch is open?


How much oil and where? I've got gauges and a vacuum pump and even a scale, so I'm planning on charging this myself. Where does the oil go? Just in the compressor? Or does some go in the accumulator, or even in the condenser? And how much?

Anything I'm missing?
 

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I think the stock Elco just uses one pressure switch, not sure if its a low or high pressure switch though. Are you using a new compressor? I think most of them are pre oiled prior to purchase but if not I've seen the oil added into the compressor via one of the hose connections on the compressor prior to installation onto the engine.
 

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1979 El Camino (yellow), 1979 El Camino (blue)
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Discussion Starter · #3 ·
I think the stock Elco just uses one pressure switch, not sure if its a low or high pressure switch though. Are you using a new compressor? I think most of them are pre oiled prior to purchase but if not I've seen the oil added into the compressor via one of the hose connections on the compressor prior to installation onto the engine.
I found this picture of an 86 Regal, that uses this switch:AC Clutch Cycle Pressure Switch for GM / Camaro / Chevy / Buick (R134a) A/C | eBay I think this is the switch that cycles the compressor. I think the high-pressure switch is just to protect the system.
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And I believe the early G-bodies, like mine, used a thermostatic cycling switch to control the compressor. This one: https://www.opgi.com/cooling-heatin...tic-cycle-switch-1976-79-gm-w-ac-ch28932.html So I'm not sure if I should leave that in place to signal the PCM to turn on the compressor, or bypass it and use the low pressure switch?

I guess the hot/cold lever doesn't set the cabin temp? Is it just AC cycling on and off?
 

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I found this picture of an 86 Regal, that uses this switch:AC Clutch Cycle Pressure Switch for GM / Camaro / Chevy / Buick (R134a) A/C | eBay I think this is the switch that cycles the compressor. I think the high-pressure switch is just to protect the system.
View attachment 135798

And I believe the early G-bodies, like mine, used a thermostatic cycling switch to control the compressor. This one: https://www.opgi.com/cooling-heatin...tic-cycle-switch-1976-79-gm-w-ac-ch28932.html So I'm not sure if I should leave that in place to signal the PCM to turn on the compressor, or bypass it and use the low pressure switch?

I guess the hot/cold lever doesn't set the cabin temp? Is it just AC cycling on and off?

My only concern with bypassing would be dealing with idle compensation with the PCM. I'm not familiar with how GM PCMs work in that regard. For my Sniper setup, the A/C kick is triggered with a ground output. The A/C control panel sends out a +12V signal so I split that output both to kick on the compressor as well as through a relay to trigger the grounding of the Sniper's A/C output.
The hot/cold lever in the interior is just an adjustment via blend door of how much hot and cold air makes it's way into the cabin through the heater core and A/C evaporator. What you have pictured looks just like my setup.
 

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Discussion Starter · #6 ·
The PCM has an AC request input line. Instead of running the request from the evaporator direct to the compressor relay, the evaporator request goes to the PCM, which then goes to the compressor relay. This way the PCM knows when the compressor is on, and can adjust the idle and fan speed.

After doing some more reading, I think I want to bypass the original thermostatic cycling switch in the evaporator. The AC on switch in the control panel would instead go to the low-pressure switch and then through the high-pressure switch, and then into the PCM. That way the low-pressure switch would control whether AC is requested from the PCM (depending on system pressure), and the high-pressure switch would act as a safety to interrupt the request to the PCM in case the pressure is too high.

After even more reading, it looks like the low-pressure switch goes directly to the PCM, and the pressure sensor (not sure what this is, but I think it goes in the high pressure switch location), and the evaporator request goes directly to the PCM. If the PCM sees the request, and the low-pressure switch is not low, and the pressure switch is on, then the PCM commands the AC clutch.

Further, because I have a truck OS written to my PCM, the PCM will not turn on the fans when the compressor is on, because the Silverado does not have computer-controlled fans. I wired in the fans to the PCM and changed the PCM calibration to use the fans, but I don't think the PCM will use the fans for the AC. Instead, I need to write a Camaro/Firebird OS to my PCM, since the F-bodies have computer controlled fans. Maybe having an F-body tune will make things a little livelier!

Anyway, I'm now pretty sure that I have my hoses configured correctly, so I'll get them crimped. Then I can work on the wiring and the programming.
 

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What B52 said -- I have an LT1 swap instead of LS, but my experience is the same. My AC is wired like the stock 84 AC system (which was converted to R134 before the engine swap) and the AC works the same as before. And the PCM controls idle speed, adapts for load to keep the same RPM - can't even tell when the compressor cycles.
 

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Discussion Starter · #8 ·
What B52 said -- I have an LT1 swap instead of LS, but my experience is the same. My AC is wired like the stock 84 AC system (which was converted to R134 before the engine swap) and the AC works the same as before. And the PCM controls idle speed, adapts for load to keep the same RPM - can't even tell when the compressor cycles.
Maybe I'm overthinking it. This is what I want. So dashboard control switch goes to low pressure switch goes to clutch relay? And high pressure switch is not used?
 

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Discussion Starter · #10 ·
The hoses are done. I kept the high pressure switch because it was already mocked up that way, but now I'm not going to use it. Hopefully I can get them installed soon.
135844
 
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Any chance you would have the fitting sizes on the hoses?
 

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Discussion Starter · #13 ·
Any chance you would have the fitting sizes on the hoses?
I don't recall off the top of my head. Are you looking for sizes for the same swap, with 4th gen F-body condenser and Silverado compressor and G-body evaporator and accumulator? If so I can look at what I have.
BTW, I swore back in February that I would have the AC working long before it got hot here, but then a VW bus project moved into my garage, and I'm still daily-driving an un-air conditioned El Camino. That bus will be gone soon!
 

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Everything is stock 87 ElCo EXCEPT for the compressor block which I got a LS conversion block for my stock R4 compressor.
I believe the block is 8-D/High & 10-I/Low
Stock condenser.
I swore the same, but am working on it now.
 

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Discussion Starter · #15 · (Edited)
Only a year later, and I am back at this. I've got the system assembled but I can't pull a vacuum.

I've been using Rob Siegel's vintage AC book Just Needs a Recharge: The Hack Mechanic Guide to Vintage Air Conditioning: Siegel, Rob: 9780998950716: Amazon.com: Books and it's been really helpful. He suggests pressure testing to find leaks, using a nitrogen bottle and regulator. Well, I have a tig welder with an argon bottle and regulator, so I want to try using that. I need to connect the regulator to my AC gauge set, so I ordered his suggested fitting (¼ flare to ¼ NPT) https://www.amazon.com/dp/B079M6H3S4 but it doesn’t fit the yellow hose on my R134a gauges R134A A/C Manifold Gauge Set. After reading a lot and checking the Harbor Freight site I found that R134a gauges use ½” ACME fittings. So I ordered this assortment from Amazon https://www.amazon.com/dp/B07ST1JM9W and found that the ½ ACME male to ¼ flare female fits the suggested fitting, and together they go from ½ ACME to ¼ NPT, which allows me to connect the yellow hose from the gauge set to the regulator on the argon bottle from my tig welder. It remains to be seen how well using argon and a welder regulator will work.

I wanted to post this before I lost the info, as it took a long time to figure out what adapters I needed, and maybe it will help someone else.
 

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Discussion Starter · #16 ·
I've been working on the AC for a while now. I knew I had some rust on the firewall behind the AC box. I posted here (I opened a rusty can of worms) about removing it. I ended up removing the AC box completely, and rebuilding it with a kit from one of the El Camino restoration shops. It was a bunch of work, but probably necessary, as every rubber and foam piece inside the box had turned to dust. When I was done I knew all of the vacuum actuators worked, and all of the doors sealed correctly. Plus it looked good.
Tire Hood Automotive tire Wheel Motor vehicle

Hood Motor vehicle Automotive tire Bumper Automotive exterior

While I had the engine out I also reworked the harness. It was a Chinese harness that had been crudely integrated with the G-body wiring. I stripped off all of the loom, cleaned up the 12v+ wires, added in the wiring from the 4L60E gear selector switches, and made some other fixes. I didn't put loom on it because I figured I had made a mistake somewhere. I also painted the more of the engine bay with POR15. It's not a restoration-quality job, but it looks a lot better than it did.
I got the engine in and running, and pulled the harness back off. I wrapped every inch of it in cloth tape, and then put plastic split loom on it. It looks much better now.
Car Vehicle Motor vehicle Hood Automotive fuel system


Then I started on the AC. I put oil into the evaporator, compressor, condenser, and accumulator (all new). I hooked up my custom hoses with new o-rings and seals. Then I pressurized the system as described above. I found and fixed a few leaks with the Blu Goo spray, but I could not find the slow overnight leak.

Motor vehicle Automotive design Vehicle Hood Automotive tire


Finally I figured I'd just run it and find the leak with the fluorescent dye and blacklight. I finished the compressor wiring, and confirmed that the AC system really did send 12v when it wanted the compressor on. I also ran the compressor request to the correct pin in the PCM, so the PCM would know the AC was on and bump up the idle and turn on the fans. I hooked up a can of freon to my gauges, started the car, and turned on the AC.

But the compressor wouldn't cycle on! And the wire to the magnetic clutch got so hot it melted through. I checked the resistance on the clutch -- 0 ohms. And I put 12v right to the clutch, but it still wouldn't engage. It's hard to believe, but the clutch on my new Denso compressor is bad, right out of the box. I've ordered a new one from Rock Auto, and will return the old one under warranty (hopefully they don't deny it).

It's as hot as the surface of the sun here in south Florida, so I am really looking forward to having the AC work.
 

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Looks like you are about done with your hoses, but for those still working on hoses checkout Eaton's EZ Clip system.
You can make custom hoses in your own garage in minutes.
It's what I'm using, will post pic's soon.
 

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Discussion Starter · #18 ·
I don't understand what's going on with the clutch. I got the new compressor today, so I pulled the old one, and bench tested it. I gave it 12v and ground, and it wouldn't do anything. I unboxed the new one, gave it 12v and ground, and the clutch engaged just fine.
I put the new compressor in, and my wiring won't activate the clutch. It acts just like the last one. So I looked closely at the pigtail that connects to the clutch, and the wires are reversed from the connector on the clutch. Green (power) to black (ground), and black to green. That's my fault for assuming the pigtail would come wired correctly. So I reversed my wiring, and now I think power and ground are connected correctly. But the clutch still won't activate.
At this point I am putting 12v directly into the AC relay connector wiring that goes to the clutch, and the clutch won't activate. That is 12v through a 16ga wire about 4 feet long.
Am I getting too much current loss through the 16ga wiring? That is the size wiring on the pigtail, and on the compressor itself. This shouldn't be that difficult.
Any suggestions are much appreciated. I'm leaving town for a few days in the morning, but will check this thread.
 

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You have to have some freon in the system or the clutch will not engage.
Or you can bypass the low pressure switch on the accumulator with 2 male spades and a wire to check the clutch.
 

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I don't understand what's going on with the clutch. I got the new compressor today, so I pulled the old one, and bench tested it. I gave it 12v and ground, and it wouldn't do anything. I unboxed the new one, gave it 12v and ground, and the clutch engaged just fine.
I put the new compressor in, and my wiring won't activate the clutch. It acts just like the last one. So I looked closely at the pigtail that connects to the clutch, and the wires are reversed from the connector on the clutch. Green (power) to black (ground), and black to green. That's my fault for assuming the pigtail would come wired correctly. So I reversed my wiring, and now I think power and ground are connected correctly. But the clutch still won't activate.
At this point I am putting 12v directly into the AC relay connector wiring that goes to the clutch, and the clutch won't activate. That is 12v through a 16ga wire about 4 feet long.
Am I getting too much current loss through the 16ga wiring? That is the size wiring on the pigtail, and on the compressor itself. This shouldn't be that difficult.
Any suggestions are much appreciated. I'm leaving town for a few days in the morning, but will check this thread.
I've been following your thread the last couple days as i am also hooking up my LT1 wiring for my A/C now as well, using the Denso Compressor. what i noticed on my LT1 wiring but you didnt mention on your LS wiring was a diode. mine has a inline diode between the compressor and Low pressure switch. i hooked mine wiring up so the diode was included. does your harness have this? IDK, this might be your issue??
 
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