A/C layout?

[Riveted1]

Anyone have a diagram, pic, crude drawing, etc. of the ac system on a '72 burb w/front and rear AC? I'm having a hell of a time finding someone in my area to fix this thing, and so I'm thinking of taking it on myself. PO replaced some of the parts and started the r134 conversion, but I think there is a little "engineering" going on here. I looked through my factory assembly manual, but I couldn't find it (I hate that book! So unorganized!)

Thanks!

[AzDon]

Yeah.... I bought a factory wiring schematic that makes no sense!
What is it that you are unclear about? Is there stuff missing? The underhood layout is basically the same on all GM vehicles from that era to present. The only difference with dual air is that both the high and low pressure lines have a "tee" in them for the lines to the rear. Front and rear can each be wired to run independently since the freon path is in parrallel rather than in series. The "kit" to convert to 134a is basically just the two freon fittings and some "conversion" oil. My preference is to buy the fittings seperately, a can of PAG150 oil, replace the reciever/dryer (GM has a different name for it that escapes me right now) and be sure to install a high/low compressor shutoff switch on the high side in place of the stock low switch because the system can literally explode past 300 psi, which these systems are capable of on 134.

[Riveted1]

Finally! Someone that seems to know what they are talking about!

I see the tees in the lines... that's what I was thinking was "engineered". Guess not though. Took it to a local mom and pop mechanic shop today and the guy said I needed to update my lines to work w/the r134. He said with the tees and such it's going to leak no matter what. But he wouldn't touch it himself, and he even has a burb sitting in his back lot!

It's got the updated high/low fittings and a compressor shut off switch. I don't know if they changed the dryer or not.

I did get it to hold a charge for a little while, but it leaked down overnight. Blew cool, but not cold. Tried the dye stuff and couldn't see where it was leaking. That's pretty much when I gave up and started looking for someone to just fix it before the summer temps get here. But everyone I've taken it to so far says it's too old and it's more trouble than it's worth to work on. I did get a lead on another shop that might do it. Gonna give them a call tomorrow. If not, I'm gonna fix it myself even if it kills me (or maybe buck up and just buy a vintage air kit.)

[AzDon]

The factory air (IMO) is WAY better than Vintage Air . They usta say that all the rubber o-rings needed to be changed for 134, but it didnt really turn out to be true. The newer o-rings are green and are available at any part store along with the special o-ring lube. The original pressure shut-off switch is only for low pressure and must be replaced with a high/low shutoff. It also must be in the high pressure line (small line between the condensor and the evaporator box.
Where this line connects to the evaporator, there is a plastic filter/sprayer called the orifice tube installed into the fitting. When you take the line off, you'll see the flat tab that you grab with needle nose pliers and carefully remove and replace. It has o-rings around it and may require a 1/4 turn to remove. This is the item that the liquid freon sprays through to create the misting effect in the evaporator that produces the cold.
Yout leak is probably right at the compressor clutch. It will be sticky around the perimeter and there will be a stripe of dirty oily freon on both fenderwells and the bottom of the hood from the pulley slinging what's leaking.
Good luck!

[Riveted1]

Originally Posted by AzDon

a stripe of dirty oily freon on both fenderwells and the bottom of the hood from the pulley slinging what's leaking.
Good luck!

Haha you hit the nail on the head buddy! I didn't see any actually on the compressor just now when I checked, but I will look closer in a bit. I've been trying to figure out where that oil on my hood and fender has been coming from. Didn't even think about it being from the AC!
I'm gonna attach some pics of what I'm looking at. Maybe you can tell me if it looks correct or not. Sorry, I know they aren't the best pics. Obviously there is some oil on the foam right by the high side port. That was the first leak I found and fixed.

Thanks again for your help!

[Bigdav160]

An orifice tube in 1972? I don't think so. From the factory it would have a expansion valve/POA

Looks like the hoses have been replaced. It's odd that you have a combination of clamps and crimp fittings. I see the oil return line is that a POA under the foam?

[Riveted1]

I think the thing under the foam is this. Not real sure though.
Are clamps ok for r134 systems? That's what the mechanic at the last shop was telling me I needed to replace. Said they should all had to be the crimp-style to work.

Also, now I'm confused as to if it's supposed to have an orifice tube or not.

Gonna try to go out there today and see if I can tell if it's been leaking around the compressor clutch. If that's the case, what's the solution for that?

[AzDon]

I see a lot that I don't like the looks of.... Lets start with the first pic:
The line coming out of the top of the evap box is the low-pressure return line. Right where it comes out is where there is supposed to be the GM drier can (shiny aluminum looks like a 24oz beer keg.) The drier often has the low-pressure freon fitting and low-pressure cycling switch screwed onto it. In your pic, it appears to have been deleted and the switch and fitting put inline.
In the same pic, the smaller line goes into the bottom of the evap box. Where the line disconnects at the box is where you will find the orifice tube in metal tube going into the box. No orifice tube, no misting effect, no a/c!
As stated by others, all hose barbs should be the crimped type. Any hose that has 45 or 90 degree fittings on both ends will need to be pre-fit and marked for crimping because a/c hose cannot really be twisted much. Lastly, Sanden compressors look cool, but if you want good cooling at low RPMs and maximum cooling capacity, The stock GM A6 compressor is without peers! Your system, especially with dual units, is what the A6 is designed to run. I dont think a Sanden has enough capacity!
I'll assume that you have the stock condensor, which should be fine....

So to recap: Must haves:
1) the stock drier can
2)Clean orifice tube installed
3)high/low cutout switch install in high pressure line ( the small line entering the bottom of the box)
4) Low pressure service fitting between compressor and drier (or on drier)
5) High pressure service fitting between condensor and orifice tube connection
6) neatly laid out and properly crimped hoses

Good to have;
GM A6 (long style) compressor
Good luck

P.S. I'm gonna dig out my A/C book, so I can recommend it to you.... I'd also recommend getting the vintage air catalog, as it has a lot of good basic info. I'm gonna buy from Nostalgic Air next time, though, because I was mistreated when last dealing with vintage air.

[Riveted1]

Thanks again for your help, AZDon. After you told me about the drier being missing, I went and looked at pics of several burbs and trucks on e-bay with AC (don't know why I didn't think to go there before!) I only found one that had the large drier next to the evap box. All of the others had a small drier mounted above the compressor. That's when I realized that I forgot to mention (and take a pic) that the PO put a newer-style drier out on the front of the core support next to the condenser.

There is one service fitting on the POA "update kit" (the switch/fitting coming out of the evap box) and it looks like the other one is on the backside of the compressor. The switch in the POA kit is supposed to cycle the compressor on and off.

So I guess my first plan of attack would be to get all of the correct lines and then proceed from there.

[Bigdav160]

GM's first CCOT (orifice tube) didn't arrive until 1973.

You should NOT have a low-side accumulator with a TXV-POA system. The high-side drier (on the core support?) is correct. It ensures the TXV gets nothing but liquid refrigerant.

The oil on the foam near the POA is a sure indicator of a leak. The line connections, while hokey looking, don't appear to be leaking. Can you trim the foam back to expose the outlet of the POA. That small copper line doesn't look right and would add a restriction.

How much refrigerant are you putting in? Front and rear A/C is a big system.

[Riveted1]

Bigdav, thanks for the info. Yes, the oil on the foam is from a leak I think I fixed already. The coupling right there was loose. I will go out there shortly and take the foam off so I can get some pics of what is going on under there.

I did stumble across my Chassis Service Manual for my '67. It's got GREAT pics of all of the AC parts and info on how it all goes together. I wonder how much changed between then and '72, and if the '72 manual has good pics of how everything goes together for the dual ac.

Through the manual, I also found out that the thing I thought was a drier above the compressor on other ac systems was a muffler for the compressor. Learning new stuff every day!

[AzDon]

Okay.... reciever on the high side of the condensor? Does it have a high/low switch? The switch in photo 1 is on the low side line next to the low side fitting. This will NOT protect the system from excess pressure. I don't see an expansion valve at the end of the high pressure line and it looks like the line going into the bottom of the suitcase is the inlet fitting of the evap "core", so I still believe there is an orifice tube inside that fitting. I still believe that ALL firewall-mounted GM evap suitcases use orifice tubes. I believe that the GM low-side drier can was removed because I see the mount that it was strapped to. The system WILL WORK with a high-side drier and I especially like that those usually have a little window to look for bubbles in the freon.
The rear A/C units DO have expansion valves
I'm not sure exactly why someone felt the need to foam wrap the line COMING OUT of the evap TO the compressor......The only part of the systen that provides colder air by being wrapped is from the orifice tube fitting to the suitcase (because it's inbound).
Whoever set up those lines was completely unconcerned about aesthetics and was thrashin to get-r-done! Those fittings, barbs, and clamps ARE made for A/C, but really meant more for quick-n-dirty fast completion than for cleanliness and safety. The system will run up to 300 lbs before cutting off (if you have the high switch installed). At 400 psi, i've seen hoses explode! I want the crimped stuff for safety!
The A/C book I've got is the soft-cover Haynes A/C book from the parts store. That and the Vintage Air Catalog should give you all the basics you'll need. If you're sticking with the Sanden compressor, be sure to use the correct PAG oil.

When putting the gauges on the empty system, be sure the knobs are shut and know that both gauges will read with the valves shut .It is recommended that you hook a vacuum pump to the charge (yellow) line and vacuum the system as low as it will go (blue knob open) on the low side gauge. close the gauge valve (blue knob), shut the pump off and wait 1/2 hour to see if the vacuum holds. If it does, do not open any valves until you have a can of pag oil on the end of the yellow hose, punctured, and the yellow hose bled of air by slightly unscrewing it at the gauges and bleeding till you get oil. Open the low side fitting and let the oil vacuum in which may occur without having to run the compressor. The second can (freon) probably won't go in without running the compressor. You may have to jumper twelve volts to the clutch until the system has enough pressure to defeat the low-pressure shutoff switch. The WHOLE OPERATION is done using the blue, low side knob ONLY. as you run the system, the compressor will create the high-side pressure. On the gauges, you are looking for not over 300psi on the high side (red) and between 20 and 60 on the low side (blue). If you get to either 60 low side or 300 high side, stop adding freon. Actually 40-50 and 200 are about perfect!

In Arizona, because of our low humidity, you can get away without doing the vacuum process, but keep in mind that air (especially wet air) both contaminates and displaces freon in the system, and you'll lose the opportunity to use vacuum to check for leaks, so evacuation is recommended.

[AzDon]

In the last picture, there is a cylindrical section just before the bottom evap-core fitting that MAY BE an expansion valve. It would basically be a sprinkler head, pressurized by liquid freon and spraying into the evap core, creating the cooling effect. If so, it and everything from there into the suitcase should have foam wrap!

[Riveted1]

After looking at this again today, I started feeling overwhelmed. So I took it to the place recommended to me by another classic owner. They are going to look it over and give me an estimate. Hopefully the damage won't be too severe and they can get this thing back to working properly. I have taken your advice on the A6 compressor and will probably switch back to one of those.

[Bigdav160]

Don could be on to something about the evap core.

I hope it's OK to link to this members truck offered for auction. In this pic you can see the TXV mounting outside the evap case.

[Riveted1]

So does the orifice tube replace the expansion valve?

[Bigdav160]

Originally Posted by Riveted1

So does the orifice tube replace the expansion valve?

They serve the same purpose but aren't interchangeable. An orifice tube works like putting your finger over the end of a garden hose. Liquid refrigerant sprays out in small droplets. The orifice is a fixed size so an "accumulator" is placed on the outlet of the evaporator core to prevent liquid from getting to the compressor.

The expansion valve is a variable opening that corresponds to the temp of the core. It works best when fed only liquid refrigerant. That's why the drier is placed before it. Early systems like yours did not cycle the compressor and the POA valve helped to prevent freezing at the evap core.

There's a possibility that the mix of parts on your truck prevents it from working effectively.

I didn't mention it earlier but an uncommon, but possible mistake, is connecting the condenser core backwards. The liquid line should exit the bottom and the compressor line should attach to the top.

[AzDon]

Okay Big Dave--
I can see that the system IS different than the ones I've had, which were 74,76 and 83.... I couldnt see the lowside pipe in riveted's pics because of the foam wrap. Later models have the fitting at the case exit with the drier screwed onto it. Whatever kind of device sprays the liquid has gotta be right at the highside suitcase connection.
I wasnt trying to be confusing or argumenative and I'm not an expert.... just a guy that knows enough to be dangerous!
Some of the smaller details can be accomplished a couple of different ways and still work great.
My best advice is to design and lay out a system under the hood that you'd be proud to show off. Get everything crimped and assembled and take it to an A/C expert for startup and charging. The expert can then either charge it or tell you why he can't. In the end, you'll know your A/C system good enough to work it yourself next time.
When I came to Arizona in 91, I knew nothing about auto A/C and hadn't cared. After a few go-rounds with overpriced A/C guys, I learned by watching that what they do isn't all that mysterious, but rather simple! The high cost with licensed professionals is the freon recovery machines they are required to use. That machine hasta be paid for, so guess who's gonna pay!

[AzDon]

In your pic, Dave, I see the expansion valve with the thermostatic petot tube right below the lowside pipe. I also see how a bandclamp holds the low pipe and screws to the mount I thought was for the accumulator's clamp in riveted's pic. The high side line enters Riveted's suitcase like I'm used to seeing. In your pic, the highside line enters much higher. Riveted's system appears to have a piece of straight tube installed in place of the expansion valve.
I'd sure like to know if the spray setup on that truck is correct....

[Riveted1]

AZDon, no need to apologize I don't think. Everything in this post so far has been good. It seems as if my system is kind of a hybrid btwn the original stuff and some newer stuff. That's pretty much what I figured to begin with. I took it to get an estimate on repairs, so between that, the info I'm getting here from you guys, the vintage air catalog, the haynes manual and the '72 service manual, I think I can figure out what all needs to be done to get it were it is both presentable and functioning. I'm hoping I can do like you said and get it close myself and get the shop to do the finishing stuff.

[AzDon]

You are way farther to completion than I am on my 67.... It came with only a broken heater!
So far, I've got a GM R-4 compressor on a serpentine drive with the wires run for the pressure switches and I've got a rear A/C out of an 87 burb mounted. I'm gonna use an underdash heat/air/defrost unit from nostalgic air.com and plumb in the rear a/c.
One suggestion I forgot to make if you are going back to an A-6 is to go to a truck wrecking yard and get all the pulleys and brackets and a core compressor from a 73-87 pickup so that you can depend on GM engineering to keep the belts on.
The reason I like the 73-87 setup is because the compressor is on the drivers side AND you can find this setup under the hood of virtually every one of these trucks.
Compressors pulsate/surge as they run which causes the belt to jiggle and when the compressor is mounted on the upper right, the bottom run of the belt is fed from the crank pulley, so it's the slack run and it is LONG (unless it runs around a smog-pump pulley)
The R4, which replaced the A6, is short and tucks down in front of the right cyl head, so not as long of a slack-belt run.
With a serp setup, the tensioner moves with the pulses, so all of the pulsing problems were solved.
A serp setup with R4 is even better, if you can find one, but your engine may not have all the necessary mounting holes. Additionally, you'd need the reversed water pump and fan and need to convert to the tiny 105 amp alternator.

[Riveted1]

Don't know how I missed your latest post AZDon. Sounds like you have your hands full! Some good info in there too.

I just got a call from the mechanic and said he replaced the service ports. Both were leaking. Says it's holding it's charge and cooling great. So hopefully it's fixed. Maybe after the summer is over I'll get out there and clean it all up and think about switching back to the A6 compressor.

[Riveted1]

Had a couple of days with the AC. Outside temps have been around 90 degrees, which we know is nothing around here. Blows nice and cold when I'm driving, and it actually gets chilly when I'm cruising at highway speeds. BUT any kind of stop and go (which is the majority of my driving), and it just doesn't cool well.

Any ideas?

[iluvmy72]

try some of these options

http://www.discountvantruck.com/rvva...condensers.htm

[C20-67_N_MO]

Anyone seen an A/C system that is under the rear seat like mine?

If you can't read whats on the knob its for temp control.

The fan switch is on my dash on the lower left hand side.

Just thought I would share this with everyone.