Originally Posted by jimbio (Post 7045278)

I have a 1978 911 SC Targa. Presently the engine (3.0) is being rebuilt, but no A/C. Is this the time to add the A/C, secondly is who offers a dependable and complete A/C unit, third does the dash need reconfiguration, and lastly is it worth it?

Originally Posted by kuehl (Post 7047503)

Jim,

1) You can add AC at any time, engine in or out.
The benefit of doing the job with the engine out is bolting on the SC style
compressor strut mount to engine console, and if by chance your crank pulley
is not a 2 groove you'll need to bolt one on; it is a bit easier to do these 2 tasks engine out of the car but I've done both ways over the years

2) Since EVERYONE (experienced owners) knows
the stock system 'out of the box' from the factory was inadequate

Inadequate, yes. But only inadequate in the sense that more refrigerant condensing, cooling capacity, was/is needed. Don't trust me, just have a look at what Porsche first did to first address that fact.

and not reliable,

No, simply NOT the case. I have 2 911's, an 78 Targa and an '88 Carrera, both with well over 100,000 miles and other than the refrigerant laskage problem and having to replenish the R134a about every 2 years NOTHING has failed. Oops, I take that back, the front comdensor blower got VERY noisy. But the goods ne was that as a result of the fans on the rear deck I didn't need that fan so I simply removed the fuse.

If there is any question of reliability it would be due to the failure rate, life, of the thermostatic compressor clutch control. But the easiest way to tackle that problemis by adding a binary (or trinary) pressure control sensor.

otherwise you would not find thousands of posts here on Pelican or the Rennlist about AC, you know right off the bat what ever you do will need to be better. Period.

Yes, there can be NO QUESTION, historically, that you would have needed to go to one or more of the aftermarket components.

But, this be a NEW DAY. What was, is no longer, all that is left for the aftermarket sales is......SNAKE OIL...!!

The shortest path to that solution if a mixture of the old and new.

Yes, couldn't agree more... New being a 2 12 volt fans and a trinary pressure switch to control both the fans and the compressor clutch. And the leakage issue? It may very well be that preventing the engine lid condensor's temperature from rising too high might well also alleviate that problem.

The old being certain 'used' components that are simply less expensive to source used vs. new. The 'new' components being improvements. If you drop me a PM we can get you down the logical HIGH PROFIT MARGIN path.

3) Is it worth it?
Well you know that is always subjective, an opinion.
The question comes down to how hot and humid your climate is and how many days a year you want to drive your car in those situations: is your car a weekend warrior with no other occupants, or is going to be a daily driver.
I tend to look at it in these fashions:
A) Do you want the car to die before you do, are you going to really drive it as much as possible and enjoy it?
B) Engine rebuild $10k+, tranny rebuild $3k+, body and interior fixes $$$$,
stereo upgrade $500+, tires, shocks, etc. Spend all that cash and if you don't have a good AC system well ??
So the price to have a comfortable cockpit is priceless!

Originally Posted by wwest (Post 7047642)

Originally Posted by wwest (Post 7047642)

Originally Posted by Scott R (Post 7047760)

Yea, forget the 12v fan idea. That's the real snake oil. Factory could have put fans all over that rear condenser back in 78 but chose not to, and there is a simple reason why.

Originally Posted by wwest (Post 7048035)

The type (voltage, CFM etc.) of radiator fans needed did not exist in 1978, they only became readily available with the advent of FWD, and only became reasonably inexpensive with the more widespread adoption of FWD.

Besides which in that era Porsche seemed to be turning to Lucas Electric for the blowers/fans used up until about 1990.

Originally Posted by kuehl (Post 7049309)

Jimbio,
Swing over to the Pelican classifieds here:
Porsche 911 Used Parts For Sale & Wanted - Pelican Parts Technical BBS
You can do a search (tab is on the right top side of all forum headers)
for AC, A/C, air conditioning (all the logical key words) in that forum
and look for someone parting out, say a 1978-1983, 911. You want
everything they have to offer but the

hoses, drier, thermostat

Using a new drier I can understand, but why the hoses and thermostat...Both might very well be perfectly good and fully functional.

and compressor.

Sure, "scrap" what might be a perfectly good, fully functional, compressor for a rather expensive new one with substantially lower displacement volume. Is that a bit like jumping out of the frying pan directly into the FIRE...??!!

If you are serious about an ac project we can guide you in more detail.
In terms of 'vents' for your year car, you don't want a knee pad vent, rather you want the guts to the ventilation components from the evaporator box to
the vents from the 78-83 for example.

Flintstone
Glad to hear you had a positive experience with our Kuehl products; a kudo now and then does tell us we are doing something positive for our community. Feel free to contact us if you need help with your next project.

Best Regards,
Griff
I don't want no garage queens or weekend warriors in my parking spot. I want my car to die before I do.

Originally Posted by wwest (Post 7050066)

..these same hoses were widely used elsewhere in the automotive A/C industry. So just what might be the difference in our 911's..???

Originally Posted by wwest (Post 7050066)

.
Engine heat rising through the rear lid condensor AFTER the engine is shut down?

Originally Posted by wwest (Post 7050066)

... but why the hoses and thermostat...Both might very well be perfectly good and fully functional.

Originally Posted by wwest (Post 7050066)

.
So the answer might well be to provide condensor AND engine cooling airflow POST engine shutdown. .

Originally Posted by kuehl (Post 7050283)

Simply for the sake of redundancy for those, ahhh.. believers of unproven propositions,........... we will go over what is factual, well known in the 911/930 community for many many years, and discussed in thousands of threads through out Pelican, Rennlist and other sources: ....


Most cars are front engine and the compressor, evap and condenser are located in the front near one another. Hence they typically used 10 feet or so of non barrier hoses prior to the introduction of R134a in the early 90's. A 911/930 is quite different, the engine is in the back along with 1 condenser while the evaporator, drier an another condenser are located in the front, hence there is 40+ feet of hose in these makes.

That's a 4 to 1 ratio, if what your surmise is true wouldn't that mean the cars with only 10 feet of hose would lose the refrigerant at an equal ratio, 4-8 years for 10 feet, 1-2 years for 40 feet?

My best example would be our 1968 Ford country squire station wagon. I have a memory of laying the compressor on the fender so I wouldn't have to recharge the system after I pulled the engine for overhaul at 125,000 miles. That car went to the great junkyard in the sky in 1978 with ~278,000 miles and the A/C still operational.

Does the refrigerant leak out of the non-barrier hose?

Or bypass the o-rings due to over-pressure?

Yes.

Its been proven in many studies,


Name, refer me to a couple of those, if you please.

that is why barrier hose is a requirement to slow/stop the permeation leaks no matter what refrigerant you use.

But why has this issue NEVER been raised outside the Porsche community?

And, for those of us whom are experienced and wiser(??), replacing the hoses reduces the permeation rate.

No question here, newer, improved technology components abound all around us. The question "here" is would the "non-barrior" hoses work just as well if the over-pressure matter were resolved.

And, quoted from the shop manual section 800-9, " There are almost always small leaks in the system that will require that it eventually be recharged....".

I have put a LOT of miles on quite a few air conditioned vehicles in my 72 years of life and other than the 911's not one has had to have the refrigerant replenished on a "maintainance" basis.

Did you ever wonder why with the introduction of the 964 in 1989 they decided to use very expensive aluminum tubing from the compressor side lines up to the front of the car?

"Rate of permeation" or rate of rock hits?.

So, they chose aluminum tubing over "barrior" hoses, maybe there is a message there that you missed?

Yes. Heat does rise from the engine. However, as soon as the compressor turns off the pressure in the refrigerant system drops and equalizes.

Not if the evaporator vane surface area(s) are already at 33F when the engine is shut down. I have already proven that the TXV remains closed for quite an extended period of time, minutes, in this instance. Check it out yourself if need be.

For example: assuming you are operating the AC system on a hot day, let's say its 100F outside and your operating high side pressure is 280 and low side is 35. You turn off the compressor and the engine as well.

If you had a set of gauges on the system you would see the high side drop and low side rise.

I only had a low side guage but it remained at the operational low level indication long enough that I was satisfied of my theory.

In short period of time they will both equalize to,...

I guess we need to define "short period". With the evaporator already at 33F and no system airflow how long would you suppose ot might be before the TXV opened...??

let's say 100 psi for example.

If memory serves mine settled at 70PSI.

The residual heat from the engine does NOT drive the pressure back up

Nobody said the pressure had to be driven "back up", my contention is that on occasion the high pressure side is already well elevated when the engine is shut down.

because there is not enough BTU's: radiant, convection or whatever your source of heat is. Not enough BTU's .... period.

"The proof is in the pudding". Try the experiment, it should be easy enough to prove me wrong.

And since the static pressure of 100 is less than the operating pressure of 280 the chances of the system system loosing refrigerant because of engine heat are not probable.

Wrong foundation for your argument, try starting at ~290PSI, or more (R134a).

If you have faulty o-ring seals or leaks in other components you are going to lose refrigerant at a greater rate when the system operating.

No one "said" faulty o-rings nor "faulty" non-barrier hoses, just more system pressure than the system was design to handle.

Many people complain that they had their systems recharged in the summer and the following season they have lost refrigerant, however their technicians cannot find the source of leaks with either black light & dye or electronic sniffing. This is because of the slow permeation rate (xxx parts per million x given time) through the hoses was the cause and cannot be detected with the dye or sniffer.

Please note that would also be the case with my theory, the o-rings are only compromised at/during the rare times of over-pressure, same with the non-barrior hoses.

Hoses have been discussed, however you do have the only unusual Porsche here
so don't worry about. The reason we suggest to replace the thermostat is simple:
A) If you have ever purchased a used 25 year old thermostat that has 36" of 2mm nominal OD soft hardness aluminum tubing filled with a gas, that has been ripped out of a car, stored in a garaged with piles of junk on top, and the shipped to you.... well, you would know better.

No, I would use a standard ice bucket test to prove that the thermostat contacts opened and closed reliably at/near the maximum cooling setting.. AND I would add a pressure sensor switch to over ride the thermostat if system pressures warranted

B) After 25 years of operation: bellows opening and closing, contacts making and breaking .. things get tired.
:rolleyes:
Please proceed with designing of your devices and post your pics and results here when your done.