Pete Lech

Mac, I just reread your original posting. I had missed the comment about the 57-59 degrees after extended driving. It definitely sounds like your evap coil is icing up. I had an '86 that would ice up after freeway runs. It was a defective expansion valve. One symptom of this is that the temp **** has no effect on the cooling. I believe that an AC shop can tell the defective expansion valve by the readings on their gauges. It would seem unlikely that your temp sensor in the evap coil would be misplaced unless someone was in there poking around and failed to replace it properly. I haven't got far enought to find the coil in the new car yet. In the old one, the temp sensor slips inside a copper sleeve that is inserted into the evaporator coil fins.

Good luck.

Mac

It sounds like we're on the right track. All of my driving is at highway speeds and the temp rise is not always present, but when it occurs, it is after about 15-20 min. Our summer climate is 95+F / 75+%RH every day. I'm not sure I understand how the expansion valve would allow for icing, though, so Pete, how does that happen??

cecil

Mac you need to move the temp sensor. it comes stock at the top of the evaporator. in our weather it allows the unit to run to long at highway speeds. it will freeze. my mechanic moved it to the middle of the evaporator and i haven't had a problem since. this is a known fix.

Pete Lech

On my '85 the expansion valve temp sensor was inserted into a copper sleeve in throught the fins of the coil I would think if it was laying on top, it would not get a correct reading. Sorry I can't tell you where the evap coil is on the 993s. I haven't explored mine that much yet.

One more thing you can try is to turn your temp control inside the car back from the maximum position when you are running on the freeway. This may keep it from icing. But if it is really a stuck expansion valve, this won't help.

Good luck.

Ray Calvo

Did an A/C performance test last weekend. Ambient temp about 83-85 deg, moderate/low humidity. Windows/sunroof shut, A/C on normal mode. Lowest temp could get out center vents was about 49 Deg; this was independent of fan setting and was constant for over 1 hour trip I took.

Did a check of suction pressure; was reading low. Decided to add some R134. Added about 10 oz. Discharge temp while sitting in garage with windows/sunroof closed and fan on full dropped from 50 Deg to 42 Deg (suction pressure still low, tho). Haven't taken it on road; weather is presently in 70's. If it heats up this weekend will try another road test.

Haven't monkeyed with the temp sensor.

Mac

What a terrific resource this board is! Over the last week, I have noticed lowest temps at ~43F, and a brief switch off (<1 minute or so) of the compressor, will allow the elevated temp to fall back into mid/upper 40's. To me, this does sound like the temp sensor, but conceptually, don't know enough about the expansion valve to implicate it yet. What is most amazing is that we're actually THINKING and doing some science with these cars! No other car inspires such attention to detail! Hope the dealer shares my enthusiasm...because I'm not going bobbing for temp sensors in THAT dashboard. Removed the heater core from a Dodge Laser ( a very close friend, or else it wouldn't have happened) and I decided that all cars are assembled from the heater core out...with the designers simply surrounding that area with steel, tight corners, sharp stuff and soon to be leaking coolant lines until the only one who can gain access is some minature ASE time traveler. Ugh.

C4 NLW

Cecil, years later and I'm having this very same problem on my 96 993 Targa. Everything checks out on the system acc Porrsche dealer but sytem cools great at the beginnning of a drive and then stops cooling well after 20 to 30 minutes so it's clearly icing up. Do you have any idea on exactly where the sensor is located (pic) and what was involved in moving it? Any info you can give me will be great, thanks.

Nick

2Many Cars

I don't know exactly where the sensor is but there should be a tube running from the expansion valve that you can follow to the sensor. For those who don't konw (many here do I'm sure) the basic drill on an A/C system is the the expansion valve is where the compressed liquid coolant is metered into the evaporator matrix. The liquid coolant evaporates and absorbs heat as it does so. Left "on" all the time the temp of the evaporator will drop below 32 F and the condensation on the coils will freeze, blocking airflow across the coils. When this happens the system can't pass enough air to cool properly. The temp sensor on the evaporator is supposed to tell the expansion valve when the evap temp is nearing freezing so the valve slows down the efficency just enough to keep the evap temp above 32F. If the sensor isn't properly positioned then obviously the reading it's getting is too high and you'll get freezing. This is especially a problem in humid areas as the condensation is much higher and as evaps don't have a uniform temp across the whole matrix you can get partial freezing pretty easily. I'm not that familiar with the 993 system but most of that era have a simple copper tube that runs from the expansion valve to a sensor on the face of the evaporator. later cars can have electronic sensors. Either way the location of the sensor matters, especially in humid climates. HTH.

Michaelc

My A/C has never worked well in South Florida. I've had some work done to it in the past and it's gotten better, but not as cold as it shuold be. So far this season I've not seen a drop of condensation under the car. Shouldn't I have a nice puddle if all is well? I'm taking back to my local wrench first chance I get, but in the meantime does anyone have any thoughts?

2Many Cars

The condensation/draining is all a function of humidity. With the system on full cold and using outside air intake on a humid day you should see water dripping under the car. Remember though that if the system is recirculating the air it dries the cabin air so as the humidity in the cabin drops - so too will the condensation and water coming out of the drain. I believe the 993 sytem recirculates the air when you push the high A/C button so that may be why you're not seeing any water draining out, especially if the system has been on a bit before you look.

Michaelc

I don't think my recirc button works, I don't see any difference in temp or fan speed when I kick on the recirc. Given the humidity in South Florida I should see lots of water coming from the drain as in my other cars. Any thoughts would be appreciated, I like to have some idea about what I'm going in for when I take the car in. A/C is not my area of expertise....

C4 NLW

2 many cars, thanks for your response on my query.

Nick

2Many Cars

I don't notice a fan/temp difference on my car either. The recirc button just changes a flap that cuts off outside air intake so the HVAC draws air from the cabin. Nothing else should change. I believe the high A/C button closes the flap because it's more efficent to cool air that has already been partly cooled.


V8 - happy to help a fellow Targa owner

Michaelc

2Many Cars - thanks for your insite. I'm going to post for an A/C repair reccomendation in the Ft. Lauderdale area. I hate being reluctant to drive my car in the June, July, August, Septemeber months because of the brutal humidity.

01coccobet

great help,

tx