Driving my 993 last night i realised my heater isn't working right. Heat comes out of the centre vent ok but not side or windscreen or footwell. Any ideas?
Thanks

 

Doogle,

Could be a problem with the servo actuators in the trunk or the mixing valves inthe RH and LH footwells. Your symptoms are odd, though - usual problem is one side (foot, face, windshield) hot and one side cold. I don't think the center vent ONLY would ever be the only vent blowing hot. But you may have a combo component failure....

Could it be that ONE SIDE of the center vent is blowing hot and one cold? This would make more sense - I think the system splits LH and RH there. It could be hard to tell if this was the case because the air mixes coming out of the center vent. Check this out.

The most knowledgable guy here on the 993 HVAC system is "Randall G" in California. Do a 993 specific search on his name and you will see what I mean. He is also very helpful and has diagnosed many problems like this that others have had. You may want to read some of his posts and/or PM him for help.

There is also a UK website that explains the heating and vent system for the 964, but it is the same for the 993. May be some help to you:

http://www.porsche964.co.uk/technical/servos.htm

 

doogle,

I'm in the last stages of dealing with this kind of problem. I agree with Mike that your description sounds a bit odd, so if you could take a closer look at the hot vs cold air and the settings.

Put the temp gauge all the way to hot and turn on the fan at 2
Turn the foot well air to high - are both sides hot or cold or is one side hot and one side cold?
Turn the windscreen air to high - do the same comparison
Turn all the air to the center ducts - not check all 4 ducts. The middle duct will mix some so compare the far right and the far left ducts.

My symptoms were:
Foot well air to high - driver side was hot and passenger side cold
Windscreen air to high - driver side was hot and passenger side cold
Center ducts - far left duct hot, far right duct cold, center duct in the middle

Let us know the outcome and Mike and/or I can potentially provide the solution.

-Skip

 

No guessing allowed when it comes to analyzing CC (climate control) problems.

Take the your car to a shop that has the Porsche PST2 to properly determine
what's the real problem. That tester can "drive" all the CC actuators and
easily determine the system faults. Most/all CC problems are external to
the CCU (climate control unit).

The Porsche CC system is NOT easily diagnosed on a forum, which can result
in wasted time and money by guessing as many have learned!

 

Doogle,

The high probability is that your problem is in one of the servo actuators or one of the mixing valves in the footwells. As Skip described above, if you can relate specifically the symptoms (where do you blow hot and when) it is not hard to diagnose the "culprit(s)". Again, "Randall G" is a real pro on this stuff and VERY helpful, as you can see from the many Rennlisters he has helped.

Even if your going to take your car to a qualified Porsche shop, it is nice to know what the problem is before you turn them loose on your car at a T&M rate.

 

Thanks for your replies,
It was definitely blowing hot from the centre vents and cold from the others with all vents open.
Today it seemed better on the return journey (about 3 hours) but got slightly worse towards the end. So i tried a bit of experimentation - I turned the heat up full and turned off all centre vents and just left the windscreen and then footwell. They blew warmish, then I teurned the centre and side vents on..the centre ones were red hot and the side ones warmish too.
Very strange..so when I get time I'm going to read the info in links you gave and try and work it out before I shell out $ or £££££ in my case!
As you can see I am new to Rennlist...and I am amazed at the response. Everyone is so willing to help, thanks again.
Don.

 

Don,

The HVAC system on the 993 is a bit peculiar and it can be a challange figuring out how to use it, let alone diagnosing a problem. Sound like you're on the right track.

You'll find most people here to be very helpful, especially if you use the archives and your owners or shop manuals to do your homework first. I think its a good idea to diagnose the problem your having first and then point your technician in the right direction.

 

and this has happendd to me today !

only cold from the left side but hot works on the right side = servo or mixing values it is !

although to compound the problem no A/C is working on the right side as well.... I assume it's part of the same mixing problem ???

 

New to the 993 meself but I see that the heat exchanger seems to have a resdesingned air dump compared to the old 911-964 valves. Is each heat exchanger's air dump controlled by the CCU? Could your symptoms be that one exchanger is not allowing warmed air to enter the system? Hence the one sided effect?