I spent the day at Road Atlanta watching the American Le Mans series in the hot sun. My car sat for hours in the hot sun and needed about 10 minutes for the AC to cool it down. For the first 20 minutes of my ride home the AC was on full and very cold. after that it seemed to get warmer and stayed only slightly cool for the rest of my trip home. (about 30 minutes)
I was at highway speeds and the car was otherwise running cool (oil temp).
This has happened once before on a hot day and the next time I drove the car the AC seemed fine.
Lastly, I expected to see some water one my garage floor when I parked it, but I didn't see a drop... clogged drain tube? Maybe time for a freon charge?
Any ideas?

 

First guess would be the drain tube. If were low on Freon you should notice poor performance always as I remember.

 

Another possibility is your charge being too high, and your compressor is tripping off on over-pressure.

 

I am thinking drain tube also. Does anyone know where the tube exits the car? Can you just clear it with a straightened coat hanger or something?

 

Kevin,

Your condenser iced up. That's why the A/C still operated (somewhat) on the last part of your ride home.

If the A/C has been operating properly till now, then your drain system is OK. If you had looked under the car 1/2 hour after you parked it in your garage, you would have seen a big puddle from the ice melting and water draining off.

If the system, at other times, is "blowing cold", then your charge is ok as well. "Blowing cold" is relative, but if your want, you can buy a cheap dial thermometer with a probe and stick it in the center vent. These thermometers are the kind the HVAC guys use to check heating and cooling vent temps. Cost about five bucks. The probe will fit into the center vent and leave it there on one of your drives.

Porsche service manuals have a chart that shows ambient versus interior temp to be expected at the center vent. I can fax your a copy if you want. Basically, if you're "blowing cold" at 55 F or colder, you're doing good.

These A/C systems are not that robust, as you probably already know. And, for some reason, the condenser will ice up and impede the performance even more, with the right combination of outside temp, humidity and "heat soak". How do I know this? Same EXACT experience last summer as you had, only at Watkins Glen 2x. Your description is precisely what happened to me. Then I spent days trying to figure it out. Conclusion is that this "ice up" problem is a peculiarity of this system and if the A/C drips and blows cold (55 F or colder) at other times, you don't have a problem.

Email me your fax # if you want this chart. I'll bet you a steak dinner that you have no problem, so don't waste your time. Your can check the center vent temp as I described above, if you want to satisfy your curiousity.

Hope this helps.

Mike Cap
1997 C2
Arena Red

 

Mike.....The logic of your assessment sounds very good. I have a similar problem, the first 30 to 45 min. it blows very cold then I would say it looses is tempeture by 50% +/-.
Then the car sets 30 to 40 min. or longer (big 'ole puddle of water underneath BTW) and it does the same thing. So lets say all I have to do is, if it's freezing up, when the car starts cooling down, just adjust the tempeture selector from full cold then it should cool without freezing-up?

Cheers <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

 

Steve,

I haven't had the opportunity (fortunately) to experiment the way you describe, as it has only happened to me 2x since owning the car. The weather up here does not have anywhere near the number of temps and humidity that you do in Texas.

Your logic is sound, though - if you lower the "load" on the A/C system, then it should reduce the icing. That being said, there is a big difference between a my 2x in two summers and your every drive. The posts I've read from the guys in the south don't have a consistent problem like yours, only intermittent like mine and Kevin's.

I think you may have a problem with a temp sensor or overcharging that creates this problem every drive. You may want to search or do a post specifically to the guys in the south and see if they have a consistent and repeatable problem like yours. Also, do you have a shop that is intimate with the 993 A/C system? The 993 owners in your area may be able to reccomend someone.

Mike Cap
1997 C2
Arena Red

 

Mike,

Thanks again for the intresting thoughts, actually, this has only happened 3 or 4 times this summer. The humidity was 70%+ and temp. 85 deg+.
I'll get on the hunt for a 993 A/C man in this area and I'll pay closer attention to the relationship between humidity and tempeture. In the interim I'm going to stick a thermometer in an exit vent and check that (I'll post that info.), it feels a lot cooler than 55 deg.

cheers <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by mike cap:
<strong>Kevin,

Your condenser iced up. That's why the A/C still operated (somewhat) on the last part of your ride home.

... If you had looked under the car 1/2 hour after you parked it in your garage, you would have seen a big puddle from the ice melting and water draining off...

</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Thanks Mike. I thought the same thing about the condenser as it has happened to the system on my house before. The weird thing is I looked specifically for the "puddle" and didn't see anything.

Does anyone know where the drain tube is? I would like to check it

 

Kevin,

If the condeser is iced up, it does take 30 minutes or so for the dripping to start. And if you get drips from the drain slot after a normal drive, you don't have a problem.

Hard to describe where the drain is. It's in the center of the car, I think it would be just forward of where the shifter would be, if you followed the shaft of the shifter straight down to the floor pan under the car. The drain is not where you would expect it to....

It's kind of a slot, not a tube hanging out like you would expect. Water just kind of drips out of the slot.

Good luck, Kevin. And pick up a cheap probe thermometer to see what the center outlet temp is.

Mike Cap
1997 C2
Arena Red

 

Just a little follow-up here <img border="0" alt="[blabla]" title="" src="graemlins/a_smil17.gif" /> ...went for a little test ride. Tempeture about 95 deg, with a digital thermometer in side ac vent on the hwy 43% humidity. I'm getting 45-49 deg. If it's getting that cold, I guess it's just freezing up on those high humidity days!

Cheers <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

 

I guess I would still wonder if a there is a problem that allows the freeze-ups to happen. I have had a home system be low on freon and still work most of the time but freeze up on really hot days. When the freon was added it no longer iced up on really hot days.
I have never serviced the AC system so I guess it could be down on freon but not enough to shut down the compressor.

 

Kevin Mike Cap is correct. You need to find a good mechanic to relocate your temp sensor closer to the middle of the evaporator to keep the system from freezing up. A temporary but not very pleasant solution is to turn your temperature dial from coldest to half cold.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by cecil:
<strong>Kevin Mike Cap is correct. You need to find a good mechanic to relocate your temp sensor closer to the middle of the evaporator to keep the system from freezing up. ...</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">What?

 

the system has a probe in the evaporator that controls how long the compressor works. It is located near the top of the evaporator. Evaporators get cold from the bottom up. By the time the sensor (in it's present location) starts to control the compressor the system is already icing up. The sensor is located for German summers not ours