Heater Controls 78 SC
 

I drive this 911 SC to work daily. I like to have the sun roof open no matter how cold, thus, I need the heat. Does anyone understand how to use the heater controls? I don’t consider myself dolt, but between the two floor levers and the panel controls I have no idea how to work the thing. No I don't have an owners manual, but I was told they don't adequately expalin the controls anyway.

Any ideas?

John

These controls have been baffling people for years. I assume you don't have A/C in the mix. Consider yourself lucky.

For heat pull the floor levers up and all the panel control levers to the left to give you max heat to the floor. If you need heat on the windshield move the bottom (usually red) panel lever to the right. If you want a floor & windshield mix put the bottom panel lever in the middle.

The floor levers also control the heater blower fan (in engine compartment). About halfway through the lever motion it will turn on the blower fan. Without the blower fan on you should get less heat flow.

The top panel lever controls the fresh air supply and fresh air blower fan. Top lever to the left is fresh air fan off, to the right fresh air fan max on.

Pay attention now!

If you have two upper levers the left is fresh air vent control and the right is fresh air fan control. (Both upper levers still to the left for max heat)

The Middle panel lever (usually blue) directs the fresh air flow. Left for floor or right for the windshield and side vents.

Close the side vents to maximize air to floor or window. I think this applies to heat or fresh air.

"Your result may vary"

You should make sure your heater blower is working by turning the ignition key on (don't start car) then pull up on the floor levers. You should hear the fan start and feel the air. If you hear the fan and don't feel the air you might have bad or loose control valves or cables and/or damaged heater ducts.

Finally, all this assumes your heat exchangers are in good shape.

Good luck!

Lewistown?

On my 78 the engine compartment blower motor comes on with just a slight lift of either floor mounted heat control lever. Check and make sure the engine compartment blower motor is still alive and well. It's not a very efficient blower to begin with, it is designed to let the engine cooling blower airflow bypass it at high engine RPMs (relatively) and that bypassing capability compromises its efficiency significantly.

I also have a 78 SC, Targa, and back when I was driving it on a regular basis, even in winter with the top off, I would go through in the fall and adjust all the pull cables, mostly within the trunk, so that I could be sure and get maximum heat, especially in the defog mode (Seattle). All that is necessary to fully kill heating in the spring is to be sure the heat bypass valves above the inside of the rear tires close completely and fully with the floor mounted levers fully down.

Coldest night I ever experienced was in Lewistown in 63 at 50F below.

I am always amazed as to how people get baffled by the heating system in a 911. All it takes is a couple of minutes playing with the thing to understand it. But basically this is how it goes. Red levers no matter where within the interior are for hot air. So RED=HOT AIR. The levers between the seats control how much hot air you want coming in the interior. The red slider on the dashboard controls where you want that hot air. If, as indicated by the arrow pointing down, you want the air to go down to your feet, then leave the red lever to the left. If you want the hot air to go up to the windshield, as suggested by the arrow pointing up, move it right. If there is a dial control between the seats, it is for a booster fan for that hot air. If it has 3 speeds, other than off, 1 is slowest, 3 is highest. The other two sliders on the dashboard, which are not RED, control fresh air. BLACK=FRESH AIR. The top one is the fan speed and the middle one, just like the red lever below it, controls the direction of that air. It can also be mixed with the hot air if desired. Try it and you will see. For max defrost, the manual recommends lower levers up and red slider full right with the black sliders left. I disagree. For max defrost, I like the levers between the seats up and all the levers on the dash to the right. Works very well. Or if the weather is hot, maybe adjust the floor levers accordingly. And for anyone who finds the heater does not heat well enough, I suggest getting it looked at. On my two Carreras, they are furnaces. I actually enjoy the hell out of this interactive ventilation system in the 911. For one, the driver and passenger can each control how much heat he or she wants. Also, considering how utterly flat out boring it is to drive within the speed limit, it is nice to have something to play with and keep myself entertained.

Good explanation, a bit demeaning, but a good explanation.

Heater controls........

Confusion may arise from the fact that first time owners simply cannot believe the lack of reasonable heat flow even if the manual is followed religiously, "I must have done something wrong".

It takes one awhile to understand/comprehend that the dash blower speed control is absolutely and totally useless except for moving more hot airflow into the non-A/C car on a hot day. One must dig into and understand the entire system before coming to the understanding that Porsche has designed a useless blower motor into the 911.

Especially so for the models prior to the footwell mounted boost blowers for windshield defrost/defog/demist.

i did not realize the florr levers controlled the fan. i thought it was purely radom at best.

I don't know, but in my Carreras when driving in snow, I never turn on the booster fan. If I do, my wife who hates heaters bitches me out. The heat coming out is plenty hot enough. Maybe my cars are a couple of the few in proper working order.

Not to be too demeaning, but in Scottsdale how would you know?

As I said, in MT 50F below is not all that unusual.

Thank you for all the replys. For those of you who told me I should be happy I don't have airconditioning...I do have airconditioning, but I know it is a totally separate entity installed after the 911 left the factory.

Oooops....

Aftermarket A/C, 911 SC.

Been there, done that, ripped it out.

Bought a 78 SC Targa with an aftermarket A/C, some of the airflow ductwork, center dash outflow for instance, was only serviced by the A/C blower.

If you're suffering from lack of sufficient heater airflow, check out the A/C installation thoroughly. Given the condition of mine I assumed origin had been SOUTHERN, which later proved to be true, AZ.

How would I know living in Scottsdale?

Because in Scottsdale, if one gets on the highway and heads north or east, within 2 hours one will find oneself in snow in winter. Or if one heads northest, like I do plenty in winter, one will find oneself in Colorado. After all, Scottsdale is in the southwest where there are plenty of mountains. Because of these mountains, even though it might be warm in the lower regions, it can be very cold up in the higher altitudes during snowstorms. So that is how I know living in Scottsdale.

Scottsdale...

Choosing to drive into cold weather is not exactly the same as living within the environment each and every day throughout the winter. I have taken my 78 Targa over and to Snoqualimie pass in the winter many times, but winter in MT, no way. It just barely provides enough heat to keep the windshield defogged, let alone providing some reasonable level of human comfort, here in WA in the winter.

I find the heat in my SC to be adequate as long as the floor levers are up. This includes dead of winter as well. The defogger, however, is another story. It just seems to deposit moist air on the glass. If it is raining or real humid, I might as well pull over. I thought perhaps my heat exchangers were leaking, but they look solid. My mechanic can't find any problems either. Any ideas from those of you with working defoggers?

Have you checked that the heat exchanger flaps are opening properly and that all the requisite hoses are in good shape?