It's hot out and A/C is pumping out nothing but heat

[Napa911]

I just bought myself a 1994 911 C2 Targa. The air
conditioning seems to be OK when the car first gets started, however after about 30-60 minutes on the road things start to heat up and I have NO AC and tons of heat. The car had an AC servicing and dye placed in the system in 2004 - so obviously this is not something new.

Is this a common problem and is there a solution?

[herman maire]

Check the 964 forums .... Down near the bottom of the page there are a few A/C treads on your 964.

[kuehl]

Originally posted by Napa911
The air
conditioning seems to be OK when the car first gets started, however after about 30-60 minutes on the road things start to heat up and I have NO AC and tons of heat.

The 964/993 are a bit more complicated than the early 911,
with the changes in the evaporator box and climate control.
Shooting from the hip, if the ac works fine when you first turn in on and starts to warm up, as you noted 30-60 mins later,
however if you try turning if off for 15 mins and then resume using it and it works fine again, it "could" be that the evaporator core is icing up. See if this is the scenario.

[elpello]

I had the same problem with my A/C in my 87 Carrera. My evaporator core would ice up about 45 mins after I turned it on. I would then turn the A/C off and a good amount of water would come out of the evaporator drain hole. It was because there was not enough R-12 in the system. I had it serviced and it worked fine after that. The A/C system is the 964 may be a little different but not by much. I hope this helps.

[DonMo]

A couple of things to check. 1) Low freon icing up the system (likely) or if too low, the high/low cutoff to the system switch may be cutting of the compressor so it doesn't self destruct. Not likely the high pressure cut off if you had it checked and charged a couple of years ago but it could be. Higher outside temp causes higher operating pressures.

[Napa911]

Thanks for the input - Now here is one other thing I have discovered. With the top in place and the windows rolled up - the AC seems to run just fine. I was on a 1 hour drive last night and it was about 72 outside and I had the A/C on and the car never heated up in the same way that it did with the top off. With the top off and 80+ degree temp seems to be when things heat up -

Napa911

[Jim Sims]

Did the A/C work well in hot temperatures before with the top down before or is this a new requirement you are applying? I doubt your system is designed to work very well "open loop".

[kuehl]

Originally posted by Jim Sims
Did the A/C work well in hot temperatures before with the top down before or is this a new requirement you are applying? I doubt your system is designed to work very well "open loop".

Jim,

We did the open-loop test last September on our 87 cab.
We had a 103-105F day, mid day sun, driving at 45 with the top down we achieved 39F on center vent at 50% fan speed, using the Kuehl 4 condenser system and the Kuehl serp evaporator.

But were very disappointed. We are going to revisit it again this year and we think tinted widows will improve the scores and if we cheat a little bit and turn off the heater ducts we may push it down to subzero.

[Jim Sims]

I would assume single pass A/C systems take a lot of capacity if the cooled air is being continually being sucked out of the car; it's tough to cool the entire state of New Jersey. If the air flow in the cabriolet is arranged to maintain a semi-stagnant air "bubble" in the passenger area then one might get something accomplished with enough capacity but I have my doubts the Porsche OEM A/C configuration was intended to service such a load.

[ruf-porsche]

When I take the top off on my Targa I drive with the a/c on. The vent temp is somewhere between the high thirty and mid 40 depending on the ambient temperature. I'm sure the entire cabin doesn't get cold, but the cool breeze with the top off makes owning a PORSCHE worth while.

[kuehl]

Originally posted by Jim Sims
it's tough to cool the entire state of New Jersey. If the air flow in the state is arranged to maintain a semi-stagnant air "bubble" in the area then one might get something accomplished

Jim,

You could not have said it any better. As a matter of fact,
our glorious Governor Corzine did achieve that here in N.J. last week. However he took a different approach. Rather than using serptine condensers to chill the state he simply shut it down because our glorious overpaid congressmen and senators could not figure a way to balance the budget.
So we had a bubble like stagnant state! State workers did not work or get paid (cough, choke). The casinos, which rake in $1.3 million per day (given to the state), were closed... dahhhh. Families with little children could not visit the state parks. But guess what? They figured out a solution. Now, instead of a 6 cent sales tax we have a 7 cent sales tax. Imaginative solution! Simply amazing brain power.

Now we know why the phrase "chill out" got so popular.

Time to move to Nevada!

[Jim Sims]

"Now, instead of a 6 cent sales tax we have a 7 cent sales tax. Imaginative solution! Simply amazing brain power."

You gotta pay for the programs people demand plus make up for all the people who are doing nothing productive (both in government services and in the general population). You won't escape it by going to Nevada; a different set of problems (inquire about how a recent medical liability insurance crisis was handled in Nevada) will be waiting for you at the exit ramp.

Back on topic. A/C vent temps in an open car are a poor indication of comfort; measurements at the driver's head level or at the seat at the small of the back would be better indices.

[kuehl]

Originally posted by Jim Sims
" A/C vent temps in an open car are a poor indication of comfort; measurements at the driver's head level or at the seat at the small of the back would be better indices.

I agree with you Jim. A/C vent temps make you aware of what the evaporator core is doing but not the overall system performance to satisfy the vehicle and driver.

Last September we took our black top 87 cabriolet out for a test drive on an unusual 103-105F September day. We had various temperature scores at the vents 24F-42F or so at max fan speed and max cool while driving. However those chilly vent temps don't do much for the occupant. So we move our thermometer probe to the side and back of the driver's head and got readings that averaged 69F.

Recalling that that particular temperature seemed comfortable I did some quikie tests in the old 96 Jeep Cherookee last week. This particular Jeep's vent temp usually does not go below 40-45F as the compressor clutch disengages. I have not explored what causes the system to shut off at this temperature (evaporator freeze out sensor, vent sensor, pressure switch, etc.), however will all the vents and their locations and the power of the blower, the Jeep's a/c system is more than adequate. So we took our thermometer probe and did like tests of the air temps around the driver's head and seemed to fine that 69-72F was comfortable.

Getting back to Napa's original question, "The air
conditioning seems to be OK when the car first gets started, however after about 30-60 minutes on the road things start to heat up and I have NO AC and tons of heat.
Is this a common problem and is there a solution?".

I would have to say that:
1) No and Yes on the problem part of the question. No, it should not be happening. And, Yes, this type of problem can be common to any brand vehicle, such as when the system is not performing correctly.... such as
a) when an evaporator core ices up do to failure of the freeze out sensor, or
b) when the 964's electric temperature mixing flap motor (two of them as I recall) goes south, or
c) when the condenser fan motor fails, or etc.

Then I recall something from the shop manual where you can hook up the "hammer" diagnostic tool and you may be lucky to get a fault reading when problem is active.

So maybe if Napa responds to the previous post question,
if the ac works fine when you first turn in on and starts to warm up, as you noted 30-60 mins later,
however if you try turning if off for 15 mins and then resume using it and it works fine again, it "could" be that the evaporator core is icing up. See if this is the scenario then we'll get an idea as to whether it could or could not be a freezing condition.

Napa, sorry for straying there for a bit. I hope to hear what your test results or observations are.