STUPID question on heating system...

floydebi · floydebi's Garage

Let me start by doing the proverbial "doggy rollover and submit" - my wife and I are entirely new to the Porsche community and will be on here occassionally asking VERY fundamental and somewhat stupid questions.. So I beg for your patience! I purchased an 85 911 for my wife for our 20th anniversary... It was purchased out of state so I did what I thought was the frugal thing and hired an independant inspection on the car. The inspection came back describing the car much as the owners had - in excellent working order. Upon investigation over the past month, we have discovered that there were/are some minor and a couple of potentially somewhat major issues that need to be rectified. So much so that the inspection company refunded my fee (woohoo) and fired the inspector.

The first issue I am starting with is the heating system. Until recently, the weather hadn't really been conducive to testing out the heating system. In any event, it turns out that someone (and I am assuming it was the previous bonehead that owned it) discovered that the automatic heat control module and/or temperature sensor (under the passenger's seat) were in need of replacement. So, rather than replace them, removed the sensor and unhooked to control module. I now know that I am getting some heat that flows out of the driver's side front heat vents constantly and I cannot get it to shut off. I know I have to replace those 2 components, but my question is - allbeit goofy - if the system is automated, what do the 2 red levers near the emergency brake handle control? They do not seem to be operating as one would expect and appear to have no effect on the heat flow.... I can't find anything in the Bentley manual that even explains what they are for... HELP!!!

masraum · 07-14-2005, 04:17 AM

Hmm, usually the automatic heat cars don't have the two red levers. Usually the non-auto heat cars have the two red levers and a knob that is numbered from 0-3, but the auto heat has only a knob that is numbered from 0-9.

If you have the manual heat (knob 0-3) then the two levers should be connected via cable to two flapper valves in the back of the car. If you have heat all of the time then either the cables aren't connected or the flapper valves aren't working properly. THey may need to be cleaned or replaced.

floydebi · floydebi's Garage

Thanks masraum.... Perhaps mine does not have the auto heat system (well - in actuallity it doesn't at this time!). Mine does have the red knob numbered 0-3... I thought (based on what I could get out of the Bentley manual) that this was the auto system. Perhaps that explains no sensor under the passenger seat.. My next goofy question is - what is the red knob for? The wiring harness is not hooked to anything.. Is it another fan control?? Thanks!

Ron.G · 07-14-2005, 04:30 AM

Hmm,
Mine has auto heat with a dial that goes one two ten and one red handle right next to the E-brake......

mine does not work either. The PO disconnected the rod (or it had broken)inside the magic box between the seats.

masraum · 07-14-2005, 04:38 AM

OK, if you are 0-3 and two red levers you definitely don't have auto heat. The way your heat works is...

The red levers have a small switch that should engage as soon as either one of the levers gets pulled up a bit. That switch should turn on the heater blower in the engine compartment. Also, the levers should control the amount that the flapper valves on each side are open which somewhat controls the amount of hot air that gets to the cabin. The knob should control the speed of the fan in the back. In my car the fan was on very low on positions 0 and 1, a little faster on 2, and even faster on 3.

I'd say you need to check your flappers and then cables first.

chgrec · chgrec's Garage

I had the same questions when I bought my 84 a few months ago.....Its a kinda strange setup but I now also understand why they did it that way.....

Essentially, the heat flow is controlled by the red rotary knob & 2 levers between the seats. There is a housing around the exhaust manifolds in the engine compartment (under the engine) called heat exchangers. They are connected to duct work that route through a fan also mounted in the engine compartment. You can see the fan on the left side of the engine when looking at it with the engine lid open. Its the large black stuff. The rotary switch controls this fan (and 2 other fans located at the drivers & passengers foot-wells) and it pushes the warm air toward the cabin.

The levers open a flapper valve that is in the ducting between the fan & the cabin of the car. Each lever controls a flapper valve on its respective side of the car.

If your heat is constant on the drivers side, I would think either your lever is up (on), the cable has hung up somewhere, or your flapper valve is stuck.....

Here is a very good thread that explains the heater function both auto heat & "manual" heat.
Inane heater controls

It seems that Porsche thought it would be a good idea to have 2 separate systems to route air in the car. One for heating & defrosting & one for cool air movement.....I say cool air as there is much debate on the effectiveness of 911 A/C and if it should even be installed....but's that for a dozen or so other threads....

The owners manual does have a very good explanation of how it all works. Let me know if you don't have one and I will scan the pages of mine and email them to you....

And welcome to the club......you must, in all good conscious post some photos of your "new" car.....

Having owned 64 cars so far, this board is by far the best single spot resource for any vehicle I have ever seen.....the people here will bend over backwards to help in any way they can......You will be spending quite a bit of time on the site.....

Chris

Mysterytrain · 07-14-2005, 05:16 AM

Ok, let me add to the confusion. The two red levers between the seats have 2 functions, they open and close the valves that direct heated air into the cabin and they also turn on the heater blower located in the engine compartment. In 1984, two small 3 speed fans where added to the the heater ducts located in the side footwell carpeting to boast the hot air flow. If the car has manual heat [as your does] a small console was added aft of the shift lever with the 3 position dial to control the speed of the footwell blowers. A couple of quirky points..the footwell blower will not work unless the rear blower is working. Hence, a burned out rear blower, blown rear blower fuse or defective switches on the red levers {remember you need to pull them up slightly to engage the mircoswitch} will defeat the entire system. There are some thread here on how to remove the rear blower and just use the footwell blowers. The other quirk is that some cars came with the ablity to have the footwell blowers to turn-off and others had the blowers running in the slow position even when the 3 position dial was in the off position. My feelings on this is that the hot air is so hot that the idle footwell blowers had meltdowns. Porsche later set them up so that even in the off position they would spin slowly to avoid the fire hazard. There ya you have it. Good luck with your car...where in Upstate NY?

304065 · 07-14-2005, 05:41 AM

A good way to tell whether you have auto heat or not is to look on the options sticker on the underside of the hood. There will be a bunch of codes. Post these here and we can decode them for you, if you like.

BigKenSteele · 07-14-2005, 06:07 AM

Floyd,
The search button is your friend. I found a great 6 page article describing the system front to back, both auto and manual. It is far too large to upload here, but pm me your email address, and I will send it to you.
Ken

chgrec · chgrec's Garage

See....Look at all the help you are getting....
Is this a great board or what!

Gotta love it......

Chris

floydebi · floydebi's Garage

Unreal! This is like going to "Web MD" for the Porsche! Thank you all so much! Since it is 90 degrees plus here today, I am waiting for a cool down to start having at it.. Thank you again for all the advice/ideas. I will be back on if I run into trouble!

safe · safe's Garage

The fans are just crap. I have just replaced the flapperboxes and sort of backdated the the ducting in the engine compartment.
I get plenty of good heat, just got to have the revs up abit (above 2-2.5K).

Also the 2 levers can adjust heat independent left and right

floydebi · floydebi's Garage

I went out a did a little looking around - where are the flappers located?

chgrec · chgrec's Garage

Flapper boxes are located under the car just forward of the engine.
Here is a photo from under the car......(faint red arrow is pointing to it)

this is a photo of it out of the car

and here is an exploded diagram

there are also some photos on this thread
Heated air path

Kinda hard to get to...take the drivers rear wheel off and it should be much easier.....

good luck & happy hunting..
Chris