I have a 1995 993 with AC problems. The fans moves a lot of air without the AC on, but as soon as I turn on the AC the flow become VERY restricted. I took it to a local mechanic and he said there were not any codes to download from the diagnostic computer. However, he believes it has a bad diaphragm control arm, and said it will cost a bit less than $1000 to fix (8 hours labor plus $100 part). Does that sound resonalble?

 

i had a similar problem and it was a loose vacuum line. it costs me about 20 mins of my labor. i don't know how someone can diagnose that without actually seeing the car....

 

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!!!!!!!!!!!!!!!!!!!!!!

That is NOT reasonable at all! You have a typical vacuum line leak. This should cost you $$$ZERO$$$.

Read this: http://p-car.com/diy/acdiag.html

It is true that you MIGHT have a bad diaphragm control arm... whatever that might be... but there are thread after thread about loose vacuum lines and NEVER have I heard of a broken arm. This is a very typical problem. Try that and then report back with what you find and we can help.

 

After the mechanic diagnosed the "problem" I went back to their shop without notifying them and picked up my car to drive it around for the day. They agreed that I could take it since no parts were delivered yet.

I was amazed to find that the AC worked fine as soon as I turned it on. I called the mechanic to ask him why he recommended such an expensive repair when the problem seems to have disappeared. He told me one of his guys opened/closed the "bad" diaphragm during the troubleshooting process. He said this would allow the AC to work, but not the heater.

After hearing that, I took the car on a second drive and was amazed to find the heater worked fine. I switched it back to AC and that worked fine as well.

My GUESS is that there was a vacuum leak that somehow got sealed durng the diagnosing process. Another POSSIBILITY is the mechanic was trying to find a way to perform work that did NOT NEED to be performed. I all I can say for sure is that I am extremely happy that I did not spend $1000 on a problem that seems to have gone away (knock on wood).

After all of this, the mechanic is still insisting on replacing the "bad" diaphragm and control arm. But I see no reason to spend any more time or money on this at this time. Thanks for the info Brian and Boris. I really appreciate it!

 

Take some of that money you saved and buy a rennlist membership, ********!

 

Great news!

By the way, there is nothing vacuum related to the heating system - unless you are talking about switching to recirc with the heat on to avoid having too much cold air forced into the fresh air vent while driving. I wonder what they would tell you if you asked them what the part # was that they ordered. Anyway, glad to see you beat the $y$tem.

And topped off with a dedication to Ray!

 

How does one top up the refridgerant for the ac.....my ac is cool....but not cold....yes I did a search using refridgerant and came up with 5 thread.....all talking about adding but none saying how to!!!

I have the little device that plugs into the system......which port does it go in?

Thanks for any helpful replies

 

David,
your fresh air vent may be open/partial open... my servo was dead and left my fresh air vent open half way. Check for its operation by putting your hand over the freash air intake below the wind screen first...

our freon system operates at 15 to 20 psi at 2000 rpm. check the pressure first on the low side before adding freon.

George

 

George
Thanks for the reply.....will check fresh air but think that is ok. How do I check the 15-20 psi reading, cant see anything on the p-car site. Then assuming everything is ok....how do I top up coolent

 

David,
to do it properly you would have to go to your trusted local garage and have them hook your system up to check both high and low pressure side... most A/C systems in cars operate on 35 - 45 psi... but not 993s...

or, you can just hook up to the low side via one of those gauges from a refill bottle and run the engine at 2000 rpm and see what the low side is reading... do not over fill - like i did... overfilling will cause your compressor to cycle frequently. This is not the correct way to test the system though...

George

 

I'd agree with George David... the "REAL" way to get the right charge is to have a shop vacuum purge and then refill your system by weight to be 100% accurate.

One step down from that is to measure the pressures in the system with a manifold gauge that reads both the high and low pressure. About $75 to $90 at an autoparts store or at ackits.com. Good thing about those is that they have that nice yellow line in the middle to either add refrig or even attach a vacuum pump @ about $200 to do your own purge.

The next step down is to use the little gauge that comes with the refill kits. As George said, don't use their "OK" or "GOOD" or "GREEN" marks for what acceptable pressure is. That will blow a 993 system up. That gauge ONLY measures low side though. The real downside of that is that you are then blind to the whole system status. Comparing high to low will offer insight into other system problems such as a bad expansion valve, clogged system, poor compressor, etc. And usually their gauges only show the first real number reading at about 20psi ... already too high.

Looking at the specs for the system below, you should see pressure as follows - according to ambient temperature. With today being about - well 100 F or 36C, you should at 2000 rpms show a high side reading of 14-17 bar (205-245psi), a low side of .7 to 1.2 bar (10-17 psi), and vent temps (after 10 minuntes at 2000 rpms) of 9-13 C or 48-55 F.







So this IS capable of being a DIY - but I would agree that it usually won't be as good as a good shop can do. Also might want to verify that your footwell heat servos are fully closing too. I used to have that problem in my former 964. Just the slightest air creeping in from the back will destroy your vent temps.

 

Oh yeah David... a guy I work with lent me his manifold gauge set before and it is still sitting in his cubicle. I'll see if I can borrow it for a few days and we can maybe meet on the way home to check your pressures. I'll shoot you a PM later on if I can have them and if I'll be out early enough today. I fear it will be a late day today because I spent yesterday at Camden Yards.

 

Thanks Brian....pm'd you

 

Brian,
Thanks for the fantastic post on your findings on the 993 air conditioner.
i have a quick question regarding A/C and was hoping that youd perhaps find a moment to point me in the right direction.

After a frustrating series of diagnosis, (incl sealing the fresh air vents permanently..) i've decided to go with the shops advice to flush the coils and recharge the system.

Do you have any specific advice that i should follow?

i understand from your post that the correct values are such
high 205-245 psi
low 10-17
@approx 36degrees

Thanks in advance... (tropic heat and a failing A/C is pure torture )

 

Hi... You are welcome. Always glad to help.

I would say that a system refrigerant flush and PROPER recharge is a good thing if you can't get your vent temperatures where you need them to be. Your numbers listed above for what the system should read at 36 degrees celcius is pretty much dead on. The only bit of advice is that if an independant (non-Porsche) shop is doing the fill, make sure they do the exact specs listed and NOT their normal specs for a normal car. Normal refrigerant levels is way too high for a 993 and you will never get the pressure drop needed to get the cooling cycle working in the evaporator.

Also, the proper high and low side pressure readings will be required to accurately diagnose any suspect components in the actual refrigerant system.

Hope this is helpful. Good luck.

Brian