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Cooling a vintage Suburban

Landyot on Sun June 20, 2010 11:59 AM User is offline

Year: 1970
Make: Chev
Model: Suburban
Engine Size: 350
Refrigerant Type: 134
Ambient Temp: na
Pressure Low: na
Pressure High: na
Country of Origin: United States

Haven't been here for years, can't believe I remembered my log in info. You guys helped me sort through a low-buck r134 conversion on my '75 de Ville, of course the low-buck part ended up costing me. I'll get back to that one by next summer.

Now I have a non-AC '70 K10 burb. The '67-'71 burbs had a roof air system that was sort of a mess, the '72 version was a more conventional front/rear system. I want to start from the beginning and install a front/rear system that with the newest parts I can using r134-and I want it to work. I've noticed alot of late model trucks don't come with rear ac. It is often ducted from the front to the back. I understand the difficulties created by the large cabin volume, surface area, greenhouse windows and lack of insulation. Front systems are available that have new parts and look stock, but they are for pickups. They will not cool a suburban. My question is will I be able to rig up a front/rear system that really works? The rear evaporator/blower setup can be used from '72 on up through the '80s at least, but is there a big enough compressor and condenser to actually make this work? I would like to engineer this system from the ground up, but if just isn't going to work I will skip it altogether.

If you could just point me in the right direction I would appreciate it. Thanks

Cussboy on Sun June 20, 2010 2:08 PM User is offline

How many passengers will you typically have, and what part of the country do you live? As of last year my '94 Suburban "lost" its rear AC (clogged/stuck rear expansion valve), front works fine. In Arizona summer, passengers in second row haven't had any issues this way.

Landyot on Sun June 20, 2010 6:27 PM User is offline

Central Kentucky (HUMID!!!), usually 4 passengers. I spend alot of time on a 67-72 Suburban web board, and the consensus with the guys with a/c is that front only isn't enough. Part of the problem is probably that the front system on these trucks only has one thin upper vent in the center of the dash and two round ones, one each on the outer part of the dash near the door. One of the questions has been if we couldn't creatively run some ducting to the second seat area--like later model trucks--and call it good. Everybody seems to have trouble with the rear system when using R12. And I haven't gotten anybody to claim they are successfully running front and rear air with 134. I'm not saying they're not out there, but I haven't heard from them yet.

Just to clarify about my Caddy, the low-buck failure was strictly due to bad decisions on my part. You can get good advice, but if you don't take it to heart..........

bohica2xo on Sun June 20, 2010 6:50 PM User is offline


Do you have the roof mount unit in your vehicle now? Or are you starting from scratch?

There are rear systems available to retrofit to big vehicles like your GMC Whale. The site sponsor actually manufactures a couple of them.

The OEM A6 compressor for your vehicle has enough capacity to cool the big space. In fact there is not much on the market that comes close to that capacity. Are you still running the 1970 style brackets / compressor / V belt ?

To take advantage of that pump capacity, and to cool multiple evaporators - you will need a high capacity condensor. Parallel flow condensors have improved a lot over the years, and you should mount the largest one that will fit. A condensor does not work well without airflow. You should have a proper fan shroud, functioning fan assembly & perhaps even an aux fan installed.

If you want to do the work, you can certainly de-humidify & cool the inside of that vehicle.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Landyot on Sun June 20, 2010 7:07 PM User is offline

I do not have any a/c in my truck at all. I've only seen pictures of the roof units. It is actually mounted inside the trucks and drops from the middle of the roof running from front to back. Not attractive. I want to keep as close to stock as possible with brackets, vents etc. But I don't want to use 30-40 year old parts, at least not the ones that matter, like evaporators, hoses, condenser, compressor, etc. My instinct was that the condenser was the big issue. I have a rear unit from an '84, and I'm sure it could be tweaked to look pretty much like the stock '72 unit. But I would want a new evaporator.

bohica2xo on Mon June 21, 2010 1:15 AM User is offline

I am familiar with the old "headliner" unit, they are not very common.

The condensor is very important. A parallel flow unit like the ones Listed HERE would be a good choice. Use the largest unit you can fit into your vehicle. It is impossible to install too much condensor in your application.

AMA makes a rear evaporator assembly for install in vehicles like yours.
AMA Rear Evaporator assy.

A fresh A6 compressor would do the job. They are 12 CID, and well suited to hard running. The only stumble is going to be control. The original A6 installations for your vehicle were equipped with POA valves to prevent evaporator icing - a real issue in humid climates. The POA valve has been out of production for decades, and they have value to the restoration types.

With two evaporators & two TXV valves you will need a way to control the system. The current trend is to cycle the clutch with a low pressure switch. The A6 was designed for continuous run systems, and is not too happy with cycling. A freeze switch type thermostat could be used, but the system would still cycle.

A more elegant solution would be to fit a V7 compressor. The V7 is a big displacement compressor like the A6, but it uses a variable stroke to control evaporator pressure & prevent icing. The V7 is available with mounting ears similar to the HT6, but might require some bracket swapping or modification to mount on the vehicle. V7's are usually equipped with a serpentine clutch. If you want to stay with a V belt, the clutch from a V belt V5 compressor is a direct fit. Not a simple bolt in, but a great compressor in this application.

With a parallel flow condensor and good airflow - using 134a should not be a problem.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Landyot on Mon June 21, 2010 11:16 AM User is offline

Thanks for all the info. This will keep me busy for a while. I'm trying to do this project backwards from how I normally do things--meaning I would like to think it through as much as possible before I start collecting parts I don't end up using. Being a classic GM guy, I have only dealt with the A6. If a better compressor is available I'm all for it, and I should be up to the task if it comes down to fabricating brackets. The installation doesn't have to be original, it just has to be clean and look like it belongs, and that should all be up to me paying attention to detail. You answered my question about the low pressure switch situation. I have only dealt with those systems, in fact converting my '75 coupe with a VIR eliminator. I will have to install a new box on the firewall either way, so I can pretty much consider anything that I think might fit and will work properly. My only concern in the stock appearance department is the dash vents and controls. Thanks again.

Landyot on Tue June 22, 2010 11:14 AM User is offline

I'm thinking of trying to find a late model GM SUV with front/rear a/c in a junkyard. Maybe I can use some of the parts or at least get some ideas. So I have a couple dumb questions: What year did the v7 start showing up, so I know what year range trucks I'm looking for. And how do you tell the v5 from a v7? Thanks.

bohica2xo on Tue June 22, 2010 11:56 AM User is offline

The irony of GM.
If you look at the 1998 to 2003 S-10 with the 2.2l 4 banger you will find an ear mount V7. The biggest compressor they made, on the 4 cylinder compact truck.

The V7 was used in other places, but this is a common boneyard vehicle (around here anyway) if you are just lifting hoods to look.

AMA can sell you a new unit, or a reman Look HERE


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Landyot on Tue June 22, 2010 1:27 PM User is offline

Very weird. The s10 kept popping up while I was researching all this, but I thought it was a mistake. But did they use this compressor on Suburbans, Tahoes, etc? I will definitely be buying a brand new compressor--I won't make the mistake of using a salvage yard compressor again (my Caddy). My interest in the junkyard trucks has more to do with the rest of the system like brackets, fittings, valves, switches, maybe hoses and how the whole system is set up.

bohica2xo on Tue June 22, 2010 2:35 PM User is offline

More GM irony...

The Corvette got the V7, in a pad mount. The same V8 in the truck got different mounts, and an HT6. This never made any sense to me, unless it was cost driven.

Firebird's & Camaro's 1998-2002 5.7v8 also got this compressor.

Never made sense to me that the most capable compressor that had went where it did.

The V7 was replaced by the CVC 185 in the Delphi line. The OEM data sheet is no longer available online for the V7, but I do have a copy.

The CVC info can be viewed HERE
or the PDF HERE


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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