"..live without A/C like you can..."

Yes, being raised on a cotton farm, share-cropping, in NE Arkansas pretty much inured me against the type of heat and humidity encountered there. Were my wife not along I would likely not even turn on the A/C.

You obviously didn't read my post for anything but a reason to find some points of disagreement.

I DO NOT AGREE that your solution increases the efficiency of the decklid condenser. For the completely stock system, the decklid condenser is not the limiting factor. It is the evaporator, and the inability to transfer the cabin heat to the refrigerant. After that is addressed, then upgrading the efficiency of the FRONT condenser yields further gains.

If someone were going to do JUST ONE THING to help the AC, it's upgrading the evaporator. The fact that folks actually get benefit with things like the ProCooler give you the location of the limiting portion of the system. This ain't rocket surgery.

If it were as easy as adding fans to the decklid, everybody would have done it already, and there wouldn't be such a large market for, ummm, upgraded evaporators, evaporator blower motors, front condensers, fender condensers, etc. Ask yourself that simple question - why do otherwise frugal folks spend 20x the cash if the answer is so simple?

Your solution doesn't pass the logic test, and it doesn't pass the real-world-real-users test.

Paraphasing you:

"..if the evaporator is upgraded then the factory condensing capability proves to be inadequate to support the cooling capacity of the more efficient evaporator....

Sounds like a which came first, chicken or egg, question to me.

What I discovered via some serious, instrumented, experimentation was that on a hot day, even by Seattle standards, the compressor could NOT drive the evaporator vane/core temperature down to even 35F, the system capillary thermostant was checked an confirmed to open at 32F (ice bucked 7/8 filled with water).

I first tired simply laying a good size window fan over the '78 rear spoiler to prove out my theory, and that worked well enough to indicate that going forward would be worthwhile.

Otherwise the Sight glass NEVER filled with (pure) liquid.

One of the primary arguements against my idea seems to be more, to much engine heat. If my idea does work to improve the efficiency of the rear lid condensor then how in hell is it that the issue of engine heat arises.

WWEST,

The bottom line is that AC is a slippery slope. Not unlike brakes, engine rebuilds and suspensions. A Spal fan is the equivalent of a cool collar. Upgraded evaps and condensers are the equivalent of adding remote oil coolers. To say that the cool collar will solve overheating is a farce, as is saying a SPAL fan will fix AC. Once you have the upgraded oil cooler, or the AC condenser, of course a decent SPAL fan WILL make it better. The reason you put remote oil coolers remotely and not in the deck is the same reason you do so with AC fender condensers. It does generate heat as it is commonly referred to as a heat exchanger, and you are trying to remove heat from the engine not add it. This is not rocket science. Your statements defy logic.

If you dont want to ride the slippery slope, then dont get on it. But dont compare apples and oranges and then present it as science, when there are 100's of pages of real world testing by credible sources that prove otherwise.

If you believe that the weak leak is the Evap, then the Evap fan for air volume. Once you get this resolved, you find its not only condenser efficiency and heat transfer but also volume. Hence upgraded front condenser, fender condensers and fans. That is why the Retroaire and Kuehl complete systems work so well. They arent just addressing heat transfer, they address volume.

If you dont believe any of it, then it really doesnt matter.

But it is disingenuous to state that 2 $30 Spal fans will fix all of the inherent ineffeicncies in the Porsche 911 AC system and that it is a cheap fix that will generate ice cold AC on a stock system in most climates.
In the end, you have tested your theory where the ambient temps rarely get above 78 degrees. not too robust... to have a robust test for heat transfer, you have to be in a location with heat! Perhaps in 70 degree ambients where you dont even need AC, improving airflow over the deck condenser with a spal fan will seem to fix all of the inefficiencies... but then again, you dont even need AC there so not a good theory on which to place your reputation.

Which came first, fuel pump capacity, injector size, intake / exhaust port size, AFR measurements, intake shape, size, geometry?
Which came first, tire compounds, tbar capacity, other suspension parts, cb, geometry, alignment, driver skill?
Which came first, evap capacity, condenser capacity, air volume, driver expectations, heat transfer issues?
Which came first, speakers capacity, headunit capacity, amp capacity, wire capacity, power draw capacity?
Which came first, cam choice, timing (ingition and cam), fuel system choice, exhaust choice?
Which came first, Battery capacity, voltage regulation, fuse panel integrity, alternator capacity, component requirements?

That is true with every mechanical part of our cars. Thats why they are called "systems".

If you fix one part of a system, then if there are other weak links they manifest themselves.

That is why they sell fuel systems as systems, why elephant sells suspension kits and systems that are matched together.
its why retroaire will only sell you a kit and kuehl recommends it.

All of these are SYSTEMS. Each component works in concert with each other.

based on your logic, I can change my tbars and not worrry about CB, Alighment, the shocks, Tie rods, bushings because I changed the tbars. I can change my cams and not worry about my ignition timing, fuel system choices, exhaust choices. I can swap out my injectors for some big 50 pound ones and not worry about the rest of the system.

How is this any different WWEST? you are not making any sense. it defies all logic. and is proven in every system on our cars to be FALSE.
Every system needs a system approach that is balanced to get the maximum performance from that given system. If you are addressing AC performance, focusing 100% on condenser heat transfer in only the deck lid, is ignoring 90% of the given system.

To oversimplify and ignore 90% of any system just makes you sound uninformed and clueless. regardless of what system you are talking about.

Perhaps you want to believe you are right at all costs. but data that is readily available has proven otherwise.

I don't know if it's a slippery-slope issue or not, Brad. There is a certain economy to doing stuff all togehter with an AC upgrade - the drier is something you have to replace every time you open the system. Well, might as well not piss away refigerant every mile, so replace the hoses with barrier type. Now, add the cost of that up, and keep in mind that you haven't touched the basic design or technology of the original system. This is JUST to get the system so that you're not spending $300/year on Freon and tech time. Adding fans to the rear condenser doesn't even touch this aspect of the problem, and is a penny-wise/pound-foolish approach. Great, you install fans to move air at idle. Without refrigerant, so what? And how many years do you chase the refrigerant loss before you replace the hoses (to get to a non-leaky stock design)? Well, why spend money on a drier next year, when you can slap in an evaporator this year? Oh, and BTW get a front condenser upgrade and switch to R134a, and you won't have to open the thing up again, and have good climate control for years, and is applicable most everywhere.

Yes, ALL of those folks who bought system upgrades are just not nearly as smart as wwest. ROFL.

I agree with you. I meant slippery slope only in the sense that you can plan to do one thing, lets say an Evap, and you can end up replacing alot more "while your in there" at a much higher "initial" cost.

I prefer to do it right the first time. Ends up being cheaper in the end. Guess WWEST just prefers to think he is smarter than 1000's of people who have been there and done that and have the results to prove it...

The problem is, at least from my viewpoint, is that most of what you say is more in the class of Urban Legend that otherwise.


A.) The drier....

I happen to have had no less than 6 vehicles(***) converted to R134a by professionals, RECOGNIZED A/C professionals. Not one of these even mentioned the need to replace the drier. The most recent one I had done was a '92 R/awd Ford Aerostar, almost $200 (norm is ~$150.00) o-rings on the back of the Sanden compressor were leaking.

'91 Ls400
'92 LS400 (3 of those).
'88 Carrera.
'78 Targa

I had a new dryer in hand when the '88 was done but was told that there was no need to incur the extra labor charges. It's still in frunk.

B.) Non-barrier hoses.

Has anyone EVER replaced those factory hoses WITHOUT using NEW connector O-ring seals...? Or for many of you, other ancillary A/C components. So, I ask you, to your own specific knowledge, what was the actual refrigerant leak FIX?? I am of the current opinion, you're welcome to provide PROOF that I'm wrong, that excessive system pressures result in loss of refrigerant, either bypassing the o-rings or via a compressor "fuse", as is, apparently, the case in my '92 Aerostar.

With the factory system the compressor iis NOT cycled off unless the evaporator vane/core temperature declines enough to "trip" the capillary type thermostaic switch. So, how high might the system pressure get with the engine simply idling along on a HOT day in Memphis.

I strongly suspect that adding the binary switch to the high side as a secondary compressor control would forever solve this issue of non-barrier hoses. Many newer systems use a trinary switch to provide for bringing on more cooling, higher condensor fan speed, if the system pressure begins to rise too high.

Anyone make a trinary switch for the air-cooled 911 A/C system?

I knew, eventually, we'd get to this.

Request for proof of a negative.

Yes, everyone that says that the hoses are permeable are lying to sell product - no, they are permeable, but only at a certain pressure. Not only does the decklid fan now solve the AC problems inherent in the design, it also reduces the pore size of rubber hoses to smaller than R12! Now you're not making actual sense in the realm of physics. Forget logic and real-world application - now you're abandoning the laws of physics to try and make a point.

Thanks for clearing all that up, and please go ahead and have the last word.

I just discovered that the Sanden A/C compressor in m y '92 R/awd Ford Aerostar has a high pressure relief valve that opens to atmosphere if the A/C high side pressure exceeds a certain level, then resets/closes once th esystem pressure is reduced. On a '92.....

Does this seem extreme to anyone other that me??

It must be there, in the design, to over come a KNOWN circumstance, right?

The Aerostar uses a hi/lo pressure switch to control the operation of the compressor clutch, therefore an overpressure of the magnitude required to "trip" the relief valve is only likely to result from outside sources...HOT day, run HARD, A/C max use, then shutdown and the HOT engine cooling radiator in such close proximaty to the A/C condensor drives the refrigerant pressure upward...

Given the parallel of the extreme level of HEAT that might rise through the engine lid condensor once the engine is shut down after a HOT day with A/C use wouldn't our air-cooled Porsche's have to endure this same circumstance?

Does the factory A/C compressor design include this feature...?

Or may ALL A/C compressors of a certain generation.

Without the binary, or even trinary, pressure switch what method is used to prevent system pressures from rising too high..?