Everyone,

I've had my 1997 993 into the shop (very competent independent in Syracuse, NY) three times complaining about the A/C not blowing cold enough. A thermometer probe in the center A/C outlets show me the best temp I can get is about 50 to 52 degrees F. My Chevy Blazer blows cold at about 46 F, as a comparison.

Yesterday, coming back from the Vintage Gran Prix day at Watkins Glen it was 90 F outside. I had the A/C cranked up and it felt like it was blowing at it's usual anemic temp of 50+ F or so. Performance that I figured I had to live with by now. About 1/2 home it was obvious that the A/C outlet temp had gone way up and I checked it at home - outlet temp was about 70 F. I checked under the car and no dripping from the condensate drain. I shut-down the car and checked for condensate drainage about 1/2 hour later and the water was pouring out.

Obviously the heat exchanger had iced up and was now melting off. I re-started the car in the garage in the shade and let it idle for a while and checked the A/C outlet temp. It was now blowing at about 60 F. The front left fan was running.

The shop in Syracuse has "re-charged" the system so far and replaced the ballast resistor to get the fan running on both speeds. I don't understand why the heat exchanger would ice up on a hot, low humidity day like yesterday. Also, why such lousy A/C outlet temps? I assume during my experience yesterday that the heat exchanger fan operation is immaterial, since I was at 50 to 80 mph for an hour and still the A/C temp crapped out.

Help? Anyone have a name for a superb A/C shop in the Syracuse, NY area? I've searched all the treads on this board on this subject and no obvious answers.

On a side note, I want to thank all you folks for the help on this board. I've learned a lot about this car and picked out a few mods to do already (Robin's RSR mufflers, chrome tips, motor-sound airbox cover). I plan on sending the ECU to Steve W. over the winter to get the upgrade.

Any help on this A/C problem would be appreciated.

Mike Cap
1997 C2
Arena Red

 

My question exactly...

 

Some data points (few times I'll quote shop manual numbers to numnuts too cheap to buy one):

At 90 degrees ambient, outlet temperatures should be 46 to 52 degrees with fan on full. All windows closed, engine 2000 RPM, at least 10 minutes after test starts.

If you don't notice any condensate, would recommend trying to see if the drain tube is blocked. Crawl under the car and see if you can clear it out with a wire.

In any case, don't expect a 993 to give equivalent air conditioning to your Cheby. While I find the AC adequate on mine, and better than my old '84 Carrera, it can't match the icebox that my Audi A4 Avant is (where I have to dial back the AC to avoid frostbite on my fingers even on a 90 degree day). Traditional 'Murrican cars/(trucks?) are noted for their AC as well.

If the evaporator coils are icing up, you DEFINITELY have acceptable Freon levels, and the compressor, condenser, and expansion valve are doing their jobs. From your description, the drain tube is likely your problem.

 

To: Ray Calvo, Senior User

 

To: Ray Calvo, Senior User

 

To: Ray Calvo, Senior User, Pittsburgh PA

If you read paragraph two of my post you'll see that the problem is not with the condensate drain tube. It is not plugged, as water flowed out of it at a fast rate as the ice melted on the evap coils. Also, the drain drips at a normal rate at all other times the A/C is in operation.

What causes the evap coil to ice up on a 90 degree low humidity day? Never has happened before in any vehicle I've owned.

On a personal note, I don't appreciate being called a "numnuts too cheap to buy" a shop manual.
Is that the way a "Senior User" talks to a new member who has only owned his first Porsche for 6 mos? It's ******** like you that turn people off from owning these cars and wanting to participate in their enjoyment.

By the way, my airplane is a 1987 $300,000 Beechcraft Bonanza A36 - I do a lot of the maintenance on it. The service and parts manuals were $500.00 for the set and they are on the shelf at my hangar. So I'm not a cheap "numnuts".

Mike Cap
1997 C2
Arena Red

 

Hi,
I dont know about intake / exit temps but I had the same trouble. ie very poor a/c.

I was just plain jealous of my friends' BMWs and VWs with their a/c. I figured it was just a hang back to the original design and air cooling vs water.

That changed with my last re-gas.

I don't know exactly what they did but they did something. I actually have to turn it down/off to avoid getting a chill even when its hot (not v often in the UK).

The only different thing they mentioned was 'oil levels' in the a/c system (at first I thought they were trying to sell me an oil change - but apparently not).
They said oil in the a/c system was v low and they topped this up, to help lubricate the pump.

My advice find an a/c shop that knows what it's doing. Not necessarily a dealer / OPC in my experience.

Belive me if mine can cool then yours should be able to , unless of course there is a leak or some other defect in the system.

Best of luck Tito

 

Mike
There have been a number of past threads re AC problems. I'm no AC expert, but the system doesn't seem to be well understood by most AC shops & is idiosyncratic. This is one area where a P dealer may be better. E.g., recharging is by weight, not pressure, & problems can result from too little or too much. Perhaps something in this archived thread will be of use:

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=3&t=003919" target="_blank">A/C won't consistently cool </a>

Good luck & let us know the results.

BTW, don't take Ray's gratuitous comments personally, he's just ... well, he's just Ray.

 

mike cap (whoever the heck you are), I still feel you have a drain problem; it can't handle the condensate buildup, backs up and ices the evaporator. I feel this is the reason why the performance deteriorated over the trip from the Glen. I've experienced it on another car I had; fine AC initially, then after a period of driving it deteriorated and started blowing mist out the vents. Clearing the drain tube cured the problem. You say water is dripping out "at a normal rate at all other times". I wonder if you can tell what a "normal rate" is; I know I CAN'T.

Once again, my opinion. You asked for opinions; live with the responses.

Owned the car for 6 months? PLENTY of time to buy a shop manual!!!!! You ordered yours yet?

Good luck with banishing the devil from your AC system.

 

Here's the center nozzle vs. ambient temp table from the shop manual:



(This figure is actually for an R-134a equipped 964, but the 993 figure is the same. I just happened to already have this image uploaded to Rennlist from a previous post.)

As you can see from the above figure, if you're blowing at some 50F (10C), you're on the high end of what the factory considers to be acceptable--assuming ambient temperature is less than 95F (35C). As a reference, my own car is freshly charged, with a new receiver/dryer, and the lowest center nozzle temp I've seen is 48F (9C). Quite adequate for me, but I'm on the west coast.

Car & Driver did a long-term test on a '95 993. One of their biggest gripes was the A/C being barely adequate (or something to that effect) on 104 degree days. As others have suggested, the 964/993 A/C is great compared to previous 911s (you can actually say it works!), but pales in comparison to what you can get out of a low-budget American car.

As I understand it, part of the problem lies with the length of hoses the 911 uses to pass refrigerant. It starts at the compressor, gets pumped (at a high pressure) to the condenser in the front of the car, goes through the drier/receiver, then the expansion valve, to the evaporator at a lower pressure, then is passed back to the compressor at the rear of the car. So ... as you can see, the hoses run to the front of the car, then back to the rear of the car.

Anyway, even if your center nozzle temps are okay, I don't understand why your evaporator is freezing up. The evaporator temp. sensor is supposed to shutdown the system to prevent this from happening.

Well, that's all I can think of for now. Best of luck to you!

 

Okay, one more thought, Mike. If you're feeling really motivated, you can verify your evaporator temperature sensor is working correctly. Readings taken across G-18/G-22 at the back of the CCU:

0C 8.8 to 9.2 Kohm
7C 7k Kohm
20C 3.3 Kohm
25C 2.6 to 2.9 Kohm

So, at ambient temp, your evaporator temp. sensor's resistance should be close to 2.7 Kohm. After freezing up, it should be near 9 Kohm.

 

Mike,

I've got a similar problem to your situation. Temperature measures consistently 50 degreesF when the car is moving (recirculation on and max AC button pressed in). I charged it w/ a can of R134a and it's still putting out 50 degrees from the center outlets. If I let the car sit and idle sometimes the temps get down to about 45 to 46 degreesF, but the few times I did this test the ambient temperature was lower than the peak temps I did the running tests at (maybe 80 degrees instead of 90) so that may have "helped" the AC system get down below 50 degrees. It seems that the 50 degrees is so consistent that I'm wondering if that's what the system is set at from the factory to yield.

Anyways, your issue of the freezing AC system might be associated with the temperature sensor as someone has stated earlier. I've read that re-positioning this sensor might help with the situation. Most posts indicate the opposite of what you're experiencing (i.e. not enough cold so they have to move the sensor farther away so the AC system "thinks" it's warmer than before and keeps the system on longer). I believe this thermostat is located near the evaporator core inside the car.

If your AC system gets cold and then warms up and then gets cold again, you've got moisture in the system (water inside the lines, condensor, ...). The moisture freezes up and the evaporator valve can't function, the ice melts and then the system works again until the moisture freezes ...). You have to evacuate your AC system and then draw a deep vacuum of at least 29in of mercury for about 30 minutes to get rid of the moisture. Not DIY stuff unless you've got the tools/machines.

Hope this helps.

 

I know nothing about A/C on a Porsche. So I might learn something. BUT, this story is pretty similar.

My house has a moisture problem. I purchased a whole house dehumidifier last year and the humitity runs about 33-35%. About two weeks ago, the humidity suddenly went up about 5%. Wife started to complain. When I checked the humidifier, it was totally ICED UP. No water draining from unit and very restricted air flow out.

It took me about an hour with hair dryer to thaw out the unit. The cause was clogged intake filter which was choked by dust. When I cleaned and replaced the filter it ran perfectly again.

Could it be your automotive system is possibly an air flow problem over the coils and has nothing to do with R134?

 

[quote]Originally posted by WillyC4S:
<strong>Mike,

***snip***

If your AC system gets cold and then warms up and then gets cold again, you've got moisture in the system (water inside the lines, condensor, ...). The moisture freezes up and the evaporator valve can't function, the ice melts and then the system works again until the moisture freezes ...). You have to evacuate your AC system and then draw a deep vacuum of at least 29in of mercury for about 30 minutes to get rid of the moisture. Not DIY stuff unless you've got the tools/machines.

</strong><hr></blockquote>

I'll second these comments ....

 

One I drive for a little while, myy car blows a consistant 40 degrees out of the center vent no matter what the ambient temperature is.

I had an '86 911 that would literally ice up the evap coil after a brisk run down the freeway, where the rpms stayed high for quite a while. The the system would quit cooling just like you are experiencing. When back in the garage, the water would drip out of the drain hose for a long time. The mechanic said that my expansion valve, which meters the proper amount of refrigerant to the evaporator coil, was stuck open. The temperature sensor seemed to have no effect on cooling on mild days, which in hindsight, was a tipoff that the expansion valve would not shut off on command. I would think that a bad temperature sensor that went to max cold would have a similiar result.

Don't worry, your 2 weeks of summer in Syracuse are over, so you will need your heater real soon. (I worked for Carrier, but not in Syracuse, for 10 years.)