Dick964

Hi,

(I'm living in Holland so forgive me my English grammar...)

I'm new to this Forum and also new to 964 ! Driven SC's for the last 12 years and finally changed to a '91 964 Tiptronic. Really a great ride and the AC and sunroof option is also nice with this kind of weather.

But I noticed something weird...
When the engine is very hot my rear blower is also working to help cooling the engine (I understand this is normal...). The fan in the front at my oil cooler is also working (both speeds..).

Strange thing is that left and rigt sills (is this the right word for it ?? I mean the hollow body parts where warm air is also going through while the heater is on..) are also become hot. The heater is off and no warm air is entering the interior at the dashboard... Also the AC is working fine.

Is it normal that these sills become warm when the engine blower is working?

Hope you can help.

Regards,

Dick911

jimq

The oil heats up the right side sill and fender. Never noticed if the (driver) left side got hot.
Welcome and show us some pictures of the car

Slappy

The oil pipes that transfers the oil from the front cooler to the engine run down the right side of the car, so the passenger sill is typically warm, if not hot. I have never experienced the same kind of heat on the left hand sill.

jeffnudd

Yep, exactly what i was going to say, plus if the car has been running for some time on tickover i found the front wing would get boling hot too, also the air con pipes run down the other side and because the condensor is at the front aswell that side would get hot too, because the condensor will be cooling the heat tranfered from the air-con to the condensor via the pipes that run under your sill covers.

Dick964

Thank you all for your replies.

I know the oil lines and cooler are on the right side of the car and also running through the sill towards the front wing.

But I've the weird problem that both my sills are warm, not by oil lines but I think they're warmed up by hot air pushed forwards by the blower in the rear at the engine.

Some mechanic told me this is normal because the rear blower dumps the warm air from the engine in the rear wheel arches but also in the sills...
At the front of the car the warm air which is not needed, will leave the car at the underside...

Is there somebody out there who can confirm the above mentioned story by the mechanic?

Thanks in advance!

Dick

JasonAndreas

Air is pushed through the dump valves (1st image) and down the side sills to the temperature mixing chambers in the front (2nd image). If the mixing chamber doors are closed (3rd image - green arrow) the air will back up and pressure will force the dump valves to close (4th image) in the rear wheel well and exhaust next to your tires (5th image). I posted some flow diagrams HERE.

KirkF

Jason,

Impressive set of diagrams! When I finish my other 800 projects, I have to look at why I get hot air in the cabin even though the heat is off. This will be a great help when the time comes! I wonder if maybe my dump valves are seized up? Maybe I should have a look in there while the engine is out?

I assume these are part 964 572 087 00 & 964 572 068 00 in pet?

This might be Dicks problem as well if the dump valves are not closing and the hot air is only being stopped by the front air flaps?

Kirk

JasonAndreas

Faulty temperature mixing chamber servos.

They probably aren't stuck but with the engine removed it can't hurt to look. If you're REALLY looking for a new project you might also want remove them and look for rust behind the rubber mounting gaskets and while you are there check the rear axle cross-tubes, Porsche didn't bother painting the insides.

Yes they are the "Heater Control Boxes."


Even with perfectly functioning rear flaps the inner sills are warmer than ambient, internally (the inserts are metal and the bends are plastic) they should be only slightly cooler than (almost equal to) the air exiting the heat exchangers. If you turn CCU to maximum heat, turn the engine off and then close a passenger compartment door (with the windows already closed) you should here a click in the rear, that will be the "Heater Control Boxes" flaps.

Dick964

Hello Jason (and Kirk),

Many, many, many thanks !!! The pictures and the flow diagram makes it all clear to me.
I'm going to check the dump valves. In the front of the car is no warm air noticeable so the mixing chamber at the front seems to be working fine.

Thanks again,

Dick964

PS: what stands CCU for in English ?

Computamedic

Climate Control Unit

Regards

Dave

Dick964

Aha, thanks !

Dick964

With all the new information from this great forum I did some research yesterday evening at the dump valves and other mentioned parts.
But I also noticed something else:

The sills only become warm when I'm driving with my sunroof open !
When I close the sunroof and wait (still driving) for about 3-4 minutes the sills cool down again...

Is it possible that my interior temperature meter (?) is giving false information to the CCU ?

Greetings,

Dick964

Computamedic

I'm guessing here, but since the flapper boxes are operated by differential air pressure, opening the sunroof is likely to change the air pressure situation completely. Opening the windows is likely to have a similar effect I would guess.

I'm sure someone else could explain in detail.

Regards

Dave