Why does Porsche A/C work in 993 but not in the earlier cars

[webrest]

My mate Steve and I were talking today and the subject of A/C came up and he proposed this question to me.

Why is the A/C in his 993 very efficient and the A/C in my '85 3.2 rubbish?

Obviously it is a well recognised fact that the earlier models have very poor cooling as there are a million theories on how to improve the situation from the very cheap to the very prohibitive.
The layouts of the air cooled models are very similar, so why does one work and the other not.

Any definite reasons why this is the case?

R.
Dave

[schumicat]

early car was not designed to have a/c. a system was cobbled together as a kludge due to demand from US customers. the later cars were designed to have it from the beginning.

[g_vaxed]

To make a long story short... Porsche moved the 993's condenser to the place with the most airflow/cooling. Also a much stronger blower similar to that of a modern car today. Earlier cars had two condensers in two stupidest places you could have put them. I would have had more respect for the engineers had they used the underbelly or fender condenser by the time SC's came out....

[wwest]

Originally Posted by g_vaxed

To make a long story short... Porsche moved the 993's condenser to the place with the most airflow/cooling. Also a much stronger blower similar to that of a modern car today. Earlier cars had two condensers in two stupidest places you could have put them. I would have had more respect for the engineers had they used the underbelly or fender condenser by the time SC's came out....

I agree, mostly. But the real problem IMO was/is the lack of cooling airflow for the condensors when not underway. Perhaps Porsche engineers never foresaw that their "race"/sports car would be used as a DD in NYC.

The other thing that was done for the 993, and even the 964, was to provide "make-up" cooling airflow for the engine using the cabin heater fan in the very same conditions this type of solution would have worked for our 911's.

[Jim Richards]

I think the A/C in my 964 works about as well as the A/C in my old 993.

[GH85Carrera]

It is mostly a lack of condensers.

As mentioned above, the car was not originally designed to have AC.

If you get your stock system in 100% peak condition it is OK for up to low 90 degree days. If you want good AC add a couple of condensers and replace the old hoses. You can cobble together your own system is you are good at engineering. If not Griffith's can sell you a system custom designed for your car. It is not cheap but it is good top quality equipment and engineering.

[dicklague]

My 1979 Saab turbo had awful air that was broken more than it worked. The mounting bracket would break, the idler pulley bracket would break. The hoses leaked.

The 1988 turbo convertible air worked well with little maintenance. My 2001 95 Aero has worked for 13 years with one less than $100 gas top up. My wife's 2003 Aero Saab A/C has never been touched and works great.

I think it is just development and refinement and better tech.

In the 70s and 80s, the Euros did not know why us Yanks wanted air conditioning? They did build systems, but they did not have a ton of development. The Porsche was a tough problem with no air inlet grilles in front and engine in rear.

[964TargaC2]

because they dont have super secret prototype condensers and tri switches?

[brads911sc]

keep in mind that a 993 condenser is almost 5 inches thick and is an efficient design. You arent going to get the same performance on a tube and fin condenser or on a 1 inch thick condenser... which is why its disingenuous to really present the front fender as a viable option as a deck replacement if you are talking a typical 1 inch thick heat exchanger like we have in most deck or fender units. there just isnt enough surface area to really replace the deck..

i also think that the location of our condensers (deck, front but somewhat obstructed) is going to reduce efficiency.
if you took the surface area of the deck and front its probably similar to that of the 993.. but its removed from the heat, given dedicated airflow...

also remember that the 993 also had 100% more air volume in the cabin and double the evap volume. So it wasnt just about the condensers.

this is an apples and oranges comparison.

[kuehl]

Email received today from a Kuehl customer, the car is a Carrera (not a 993):


"Picked the car up at noon today, it had been parked outside in the sun all morning, heat exhausted, and the Griffiths a/c cooled it down fine for a 2hr drive."

[1-ev.com]

we have 100-113 with 95 humid air almost every second day here

[wwest]

Originally Posted by kuehl

Email received today from a Kuehl customer, the car is a Carrera (not a 993):


"Picked the car up at noon today, it had been parked outside in the sun all morning, heat exhausted, and the Griffiths a/c cooled it down fine for a 2hr drive."

Gee, my '78 Targa could do that before any mods. Ask him about Manhatten to the airport during rush hour.

[brads911sc]

Might be good if everyone stick to the original PO question...

[Uncle]

Originally Posted by 964targac2

because they dont have super secret prototype condensers and tri switches?

:d

[kuehl]

Originally Posted by webrest

Why is the A/C in his 993 very efficient and the A/C in my '85 3.2 rubbish?


Any definite reasons why this is the case?

R.
Dave

Sorry about the comparative post of an upgraded Carrera. I just wanted to bring WwEsT into the puzzle since his comments are always so helpful to the board.

The reason why the 964/993 system "seems" to cool better is a mixture reliability improvements as well as condenser/evaporator and air flow improvements. The later model air cooled brought aluminum tubing in to replace the leaking plain rubber hose. A single condenser, twice as thick as the previous generation and powered by a rather large fan in terms of cfm. The evaporator increased in size. One evaporator blower became 2 blowers. Additional insulation, better venting. Put it all together and you have what "seems" to be better system. Seems in the eye of the beholder.

Now, the reality check. Is the 964/993 cheaper or less expensive long term, say maintenance wise, as compared to upgrading the previous generation 911 systems (prior to the introduction of the 964) ?
NOPE!
NOPE!
NOPE!

Compressors? SC/Carrera ... vs. 964/993, same cost, but I'd say I see more 964/993 failures then SC/Carrera

Refrigerant lines? the SC/Carrera models were all rubber, now upgraded with barrier hoses. The later 964/993 use primarily aluminum however there sections of rubber in the engine bay and by the front fender condenser. And, some of the 964/993 model lines have custom fittings you will not find easily. The 964/993 model are now needing their engine compartment rubber lines replaced (with barrier).

Drier? same cost, but the SC/Carrera is easier to replace.

Condenser? SC/Carrera models (deck lid and front) tend to hold up quite well, but to cool these cars down you need to add more. 964/993 models have 1 condenser and they are cost affordable, however its fan is proprietary and R&R time is 3 times as long. By the way, the Boxster/996 condensers are starting to leak.

Evaporators? SC/Carrera models up through 85 hold up well to a point, most need to be cleaned by now. 86-89 bonded a copper manifold to aluminum tubes (alike late 928 units), they all leak soon. The 964/993 models are all leaking! Yes, the 964/993 all need to be replaced. Time to R&R an SC/Carrera model is 45 mins for the experienced or 3 hours for the DIY. The model 964/993.... 12 to 15 hours! By the way, the Boxster/996 evaporators are starting to leak.

Controls? SC/Carrera model thermostat and fan speed switch are cheap and easy to replace. The 964/993 model AC control heads are very expensive to repair. The SC/Carrera heat vs. AC air piping or 'flaps' are cheap and seldom fail.
964/993 model fresh air/ ac air/ heated air mixing system is more complicated and timely to troubleshoot and need the hammer (reminiscent of the over designed 928).

Evaporator Blower Motor? SC/Carrera just use one and they hold up at least 20 years, rather easy to R&R. The 964/993 uses 2 unique proprietary blower/motors, costs are 3 times just for one motor and take 5 times longer to replace.

Bottom Line
We (our firm) hear's few complaints from 964/993 owners, however that is relative to the higher ratio of SC/Carrera on the road.
When we get a phone call from a client that "needs to convert to R134a", we know its because they have a leak in the system,
if its a 964/993 owner and the leak is the evaporator... they are shocked when they research the repair time.
The average upgrade time for SC/Carrera is ranges from 15 to 22 hours depending upon the range of upgrades,
while the time just to replace the evaporator in a 964/993 averages 15 hours.
There is more competition and selections of upgrades for the SC/Carrera, just read the boards,
however when a 964/993 owner in Tucson needs to cool down there are very few choices for upgrades.
Considering the number of SC/Carrera vs. the number of 964/993 on the road today,
and the number ratio of orders we receive for replacement AC parts or upgrades.....
I'd buy the SC/Carrera and upgrade. Less expensive in the long run and much easier for the DIY as well as having a shop do the work.
The 964/993 does have some appealing attributes, such as power steering, coil overs and few more ponies......
But my Carrera cabriolet, with its ice cold AC system, reliable motronic, simple component design, and.....
3.5 liter supercharged engine.. lol, leaves them all in the dust. Just IMO, .... lol.

[hazelmrzv]

I would have had more respect for the engineers had they used the underbelly or fender condenser by the time SC's came out.

[brads911sc]

No offense was taken... we just need to try to stop feeding the troll so that he dies here and stays on the lexus forum..

Originally Posted by kuehl

Sorry about the comparative post of an upgraded Carrera. I just wanted to bring WwEsT into the puzzle since his comments are always so helpful to the board.

[webrest]

Well thanks all for the input I think I now have a pretty sound idea of what is going on.
The big question for me now is whether or not I'm going to do anything about it.
The short answer is probably no. Messy job that will cost too much versus the amount of time that I would use it.
It is always good to know how things work or in this case. Don't work.
Thanks again to all.
Dave

[flskala]

Still on topic.... This entire week I commuted to work (Northeast temps near 100 every day) in a friends black w/black interior 993. Each day we had to turn the AC down from the highest setting! Yep, you read that right! The 993's AC cooled a black/black car down perfectly and rather quickly.

Has anyone on here successfully fitted a 993 condenser w/fan in a carrera/sc? I'll admit I haven't searched but.....

[shbop]

Originally Posted by flskala

Still on topic.... This entire week I commuted to work (Northeast temps near 100 every day) in a friends black w/black interior 993. Each day we had to turn the AC down from the highest setting! Yep, you read that right! The 993's AC cooled a black/black car down perfectly and rather quickly.

Has anyone on here successfully fitted a 993 condenser w/fan in a carrera/sc? I'll admit I haven't searched but.....

I tried this on an 88'. The entire assembly was too large for the rear wheel well, however after removing the factory fan, and modifying the housing, you end-up with a condenser that will fit. We didn't want to get rid of the water tank in the driver's side front, so the rear was what we had to work with. We thought about adding a thinner Spal fan, but opted to add a Zims condenser in front of the rear wheel after making new barrier hose assemblies for the car. This third, fan assisted unit, provided the necessary cooling. The A/C now works quite well.