CosmosMoon

My question:
since the rear blower fan is always on when the heat is on, what’s the point of having the engine fan blow into into the heat system? Why not just always have fresh air blowing in and then completely block off the engine fan input to the blower?

(This ground has probably been covered before but I couldn’t find it in my searches. )

I know the rear blower helps keep the heat strong when the engine is at low RPM and acts to (occasionally) cool the engine after shut down. I also know the fresh air flap is to let fresh air come in rather than exhaust gas when the car is in reverse.

it seems like the engine could get more cooling by not having some of the engine fan air going to the heat, so why did the Porsche engineers do it that way? Why not always feed the blower with fresh air? Is it to cool the exhaust side of the engine (dumping the air out the dump gates when the heat is off)? In that case, they could have just set it up so that the blower is always on regardless of the heat - no?

I bring this up as the current iteration of the TPC supercharger has a cover that blocks off the engine fan, but they expect you to keep the blower and just have it run on fresh air, and I’d like to know the trade offs. (The old version came with an RS style bypass pipe instead)

ToreB

The rear fan is not always on. It runs in low or high speed when:
1: Heated air needed to the cabin: The cabin temperature is lower than the CCU temp **** setting.
2: Engine cooling mode: The engine (air duct) temperature is high enough
Cooling mode is only invoked when no heated air is needed to the cabin, and is active on both ignition on and off, but with different temperature thresholds.
The rear air valve selects either air from the from the upper air snorkel or the main mechanical fan, indeed depending on whether the reverse gear is engaged or not. The mechanical fan greatly improve the heated air volume to the cabin.
I don't know Porsche engineer's reasoning behind this, but assume the potential danger of sucking exhaust fumes to the cabin when reversing was weighted more than having a short period (when reversing) of less hot air pressure to the cabin.
Cheers,
Tore

CosmosMoon

Thanks Tore… I just want to mention that I’m not talking about getting rid of the blower, but instead talking about not having the mechanical fan pushing air into the blower/heat exchangers, and instead just having the blower motor pulling fresh air when there’s a call for heat.

it’s a drag as I use the heat at full blast for much of the winter since I rarely put the top on. I suppose the best way is to just try it with the mechanical fan side disconnected and see how much of a difference there is. - I was just curious if anyone thought there’d be a mechanical engine-heat-management reason for having air always moving through there from the mechanical fan, but I suppose there’s a lot of track cars (and Singers!) with no duct venting mechanical fan air over heat exchangers and they are fine.

sacman

This is one of the things that bothers me about the 993. Whenever I take my SO out for dinner at night and have to use heat, the air inside smells barely tolerable. Since there's no heat source from coolant in a water cooled car, it has to blow air cool (inside our outside) pass the engine to exchange for the heat.

QN

CosmosMoon

Just stuff a bouquet of fresh lavender in behind the cooling fan - problem solved!

"New from RennLine! Carbon Fiber RS Heater Duct with Potpourri Drawer!"

pp000830

Hi Sacman,
Have you considered you have an oil leak dripping on the exhaust burning and then getting drawn into the cabin? A leaky valve cover or a spill at an oil change can cause this and the attendant smell.
If one gets such a leak fixed, valve cover gaskets are relatively inexpensive to have changed, and the exhaust is hosed off with spray electronic cleaner the bothering may simply go away!
Andy

71-3.0-911

Something needs to be fixed on your car then. You are leaking oil, have holes in the flexible heater ducts, or have lost the reverse flaps. Oil fumes inside the cabin is not normal.

Gbos1

I don’t have this issue… as others have said you apparently have something wrong going on with your car. Get that checked out

CosmosMoon

As a follow up to this, I did an experiment and removed the diverter flap assembly from my blower motor, so the blower is no longer connected to the mechanical fan shroud. It's open on the side and just pulls the air in that way.
Went for a drive in 30degree (F) weather, with the top on. Air was blowing out of the vents the whole time - hard to tell if it was weaker than with the mechanical fan - seemed like, but tough to tell. Once the engine got up to temp, I couldn't keep the heat on high. I was only wearing a sweater, but it was just too warm in the car - especially from the dash vents, I thought my face was going to melt off.
So, while it might not be as warm as it could be, I think I'll be fine w/o the connection between the mech-fan and the blower!

fatmike

These cars smell like leather and burnt oil. It’s part of their charm.

/

Cupcar

A Clubsport 993 RS (M003) comes with a bypass pipe that eliminates the auxiliary blower and diverts air directly from engine fan to heat exchanger system.