Dans993C4Cab

Hey gang, it's been a while since I've had the chance to be online.
I've got an interesting one, at least it is to me! I heard a pop while driving the other day and all of the sudden the interior vents for the AC/Heat were blowing very hot. I turned the AC on to see if it had any effect but no. And it's been blowing hot regardless if the fan is on or not.
Any ideas?

User 122821

Most likely the climate control computer is broken or the flap valves under the engine are stuck open allowing all the heat to shoot into the vents

911Dave

You heard a POP, followed by hot air coming out of the air vents. Obviously something broke suddently. I can't imagine it's anything other than the CCU. You can get it replaced or rebuilt.

Dans993C4Cab

Thanks guys I really appreciate it!!
Dan

helmet993

The pop sound you heard, was it akin to the pop (plop?) sound the recirc door makes when it shuts, say after turning the key off or on?

Is your a/c compressor running? Is one of the lines cold near the compressor (it should be sweating too)??

You can verify all the flaps are working by running the car and having someone slide the sliders on the CCU, you can see the actuators move if you remove the cowl cover.

helmet993

Another thing, does using the large snowflake button change anything?

Here's a thread for a/c diagnosis...I've had to use it before, it was frustrating at first, but overall very very rewarding once fixed.

https://rennlist.com/forums/993-foru...diagnosis.html

ToreB

Constant heat is most often due to broken mixing flap servos. There's two of them, one in each footwell, controlling the air flow in each half of the dashboard vents. Are the air flows on both sides the same?
It's easy to open the carpet walls and spot for any movement on these servos, but you may have to disconnect the vent/servo mechanism from the heat hose to see it. Both servos are meant to open and close simultaneously when you turn the temperature setting **** on the CCU to max and minimum.
I've seen some rare cases of defective servo drivers in the CCU, but it's way more likely that one or both servos have given up the ghost.
You could also use Scantool or other OBD tools to poke any fault codes in your CCU.

I can't explain your popping sound, you may have more issues in your HVAC system. A typical scenario is inert or failing mixing/fresh air vents, and turning up the fan speed cause a vacuum, pulling the resirc flap closed with a pop. That may also be caused by a problem with the vacuum hose to the resirc flap actuator.
All these issues are not uncommon, and I have seen several cases of cars having such multiple faults.

Have a look at my DIY web site for details:
www.ccu.tore.bergvill.com

Cheers,
Tore

ToreB

winfordenning, please explain why.
Cheers,
Tore

x50type

I can't imagine its much more than the passenger side mixing flap servo - readily available from your Porsche dealer for about $300 and easily fitted in 10 minutes.

vjd3

If it's a footwell servo, it would be only one side or the other ... the OP said all the interior vents are blowing hot.

He also said all the vents are blowing hot regardless of the fan setting, which sounds like it's still blowing hot air even if the fan is turned all the way off. That would seem to indicate a CCU failure.

The Porsche system tester can check the various components and see what's going on.

ToreB

I don't agree in the conclusion of a faulty CCU quite yet, based on the information we have so far.
A much more probable cause is that both mixing servos have given up the ghost. I've seen that before, and sometimes one of them stops working before both do. Remember, an inert servo may stop in all possible postions, fully closed or open. It is therefore not always easy to registrate, depending on the time of year and need of cold or hot air.
Mixing flaps stuck in open position will always allow hot air to be blown from the engine independent of the fan setting.
Tore

bobboinski

I had a footwell servo stick open about 2yrs. ago. Gave it a few taps while cycling the heat control and it has worked perfectly since. Time to do a little investigating? The pop is new to me. Those servos don't seem like they would generate enough force to cause much of a pop.

Ish993

I had a flex duct break in the passenger footwell behind the kick panel. It was like the fires of hell were venting thru my car

x50type

I would rather try a $300 servo before opting for a $2000 CCU - which appears quite rugged.

Did i mention the 2 push buttons on the CCU are NLA but the slider ***** and 2 round ***** are!

Dans993C4Cab

Wow! Awesome input guys! Guess I've got some investigating to do! Now I know where to start! Hoping for a flex tube or servo.
Thanks again guys!