How does the heating system work for 74-89?
 

Can anyone point me to a doc that explains how the heating system works for the mid-year oil cooled cars? I searched forums but did not find any overview explanations. Thanks in advance,

Paul.

The basic system works like this:

Red tipped levers on the floor between the seats are pulled up, opening the flapper valves on the heat exchangers. This channels warm air into the cabin. The dash controls--typically three rows of levers--uses the bottom red tipped lever to direct the air to the windshield or the foot wells.

Now, there are some variations depending on the year of the car. Some cars have "auto heat" which opens the flappers mentioned above by turning a switch and small servo motors. Some cars have footwell booster fans to force more air out. The dash controls are essentially the same though--top two rows are for fresh, outside air, and the bottom red control for direction of warmed air.

Best to get a driver's manual for your particular car and read up. Failing that, post the exact year and model here, and someone with the exact car will fill you in on the details.

Try the search button on the top right of the Technical page and try search words like "heater" "dash controls".

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This is a commonly asked question, so I thought I would re-post something I wrote up for the old Porsche Email lists before the dawn of the Pelican.

Q: I just bought a 911 and can't figure out how to make the heater work -- or the fresh air either. Can you help me?

A: Sure, I can help you. The ventilation system requires that you operate 4 levers to make it work. 3 of the levers are on the dash, and the other is between the seats -- on newer Pooscheys there are 2 levers between the seats).

The top lever on the dash actually does several different things (remember, it is a fiendish German device, just like the rest of the car). Pushing it to the middle opens the dust ports leading to the windshield (see below for operation of fogging machine and oil mist spray device). Pushing it to the right past the middle also activates the rattling noise-maker device. There are three loudness levels to choose from. Pushing the lever all the way to the left is used to jam the cable so unauthorized personnel cannot operate any of the devices above. The lever also enables the automatic heat exchanger signaling device -- when opening it spews rust particles on the windshield, you should replace the heat exchangers. Also, if opening it causes you to immediately turn blue or purple (not just hair, but skin color) and become unconscious, you (or your estate) should definitely replace the heat exchangers.

The second lever from the top controls the lights on the White House Xmas tree. Move it to the middle to turn on the lights, and all the way to the right to fire 4500 Megatons of Nukes at Iran.

The bottom lever on the dash is used to replace the windshield when it becomes scratched or pitted with rock chips. It also determines how much hot air goes to your feet as opposed to your head. For example, let's say the engine is completely warmed up and the hot air is burning your feet. If it's a cold day, you can flip the lever to the other side and shoot hot air onto the windshield so it cracks and shatters. Then call your insurance company (you do have insurance, don't you?)

The lever between the seats controls the oil mist spray device. When the engine is warmed up, this lever allows you to blow oil mist into the passenger cabin. Using the top dash lever lets you select whether you want the oil mist to coat the inside of the windshield or to just circulate around your feet. On a newer Pooschey, you have 2 levers on the floor between the seats. The left hand lever lets you open the left side vents which are aimed so they burn the feet of the person in the right hand seat, and the right hand lever lets you open the right side vents which are aimed so they burn the feet of the person in the left hand seat. Of course, each lever will also burn just the tops of the feet of the person in the other seat. If you are driving in the rain (or even stopped in the rain after the car has broken down), these levers also let you spray a fog of water vapor on the windshield, so no one can see in or out of the car -- sort of like privacy glass

I think I remember reading that post back in the early '90s on the Porschephile list (Stan Hanks was "moderator"). It was funny then too.

Try these links:
03-01_911_heater
911 Auto Heat
http://forums.pelicanparts.com/porsche-911-technical-forum/438183-911-heat-questions.html
Porsche Club of America, Northeast Region

Yeah, I always loved this pic:

http://members.rennlist.com/imcarthu...ercontrols.jpg

When you figure it out please let the rest of us know!!!

How does the heating system work for 74-89?

Poorly.

Except when it roasts ya'. ;)

Good stuff!

My 85 will roast you for sure even on very cold days. I would say it works great.

Here is a complementary pic of the layout, which I obtained on this forum:

http://forums.pelicanparts.com/uploa...1265247325.jpg

heat
 

great stuff everyone. the mysteries of porsche 911 auto heat diagram is good. i was curious about the servos when i turn my heat on, ie where are they and how do they work. looks like they are the Heat Control Valve...which makes sense to me now as they are connected directly to the console between the seats. my heat works exceedingly well, and the a/c is not bad using a sanden compressor new filter etc. . love the comic review---funny stuff. really appreciate the feedback from everyone.

best, Paul.

i forgot to mention i took the car out in 20 degree weather and it took some time for the heat to finally kick-in, even though the motor had warmed up....when switching on the heat, i could hear the servo motors, but i had to drive 15 mins before the heat came on...i have a feeling the servos were to cold to operate.

which would defeat the purpose of having them as part of the heating system...!:D

You gotta love the design that has no fresh directed at the driver, just non working air conditioning.:rolleyes:

Keep in mind that the system used on a 911 is different from that in a 930; the 911 systems varied from year to year; in a 911 you could have manual or auto heat...

There are at least 6 variations that I can think of. So, don't assume that everything you see above applies to your car...

JR

If I want the creature comfort of a predictable cabin temperature other than hot, hotter and hottest in the colder months, I drive the Audi.

footwell blowers
 

Hi Can you help,
Ive just replaced the fresh air blower motor and this works!!!!:)
The footwell blowers have never worked - if I remove one and add 12V they work fine. does anyone know where they are switched from ?
Please help
Thanks Chris 1986 911 turbo bodied cab:)

The round knob between the seats, by the handbrake.

JR

This explains it well. I can't drive the car when it is colder than 50 degrees because the tires ***** and squeal at me. So the warning that came with the tires is true "these tires won't stick below 50 deg. "

My 87 Carrera footwell fans come on when the heat knobs are lifted. Round knob is part of the auto heat. I have the round knob...but not auto heat...and as near as I can tell it doesn't do anything.

There's a third system that looks like auto heat but isn't. It has a similar rotary control to the auto heat option but it is basically just a fan speed control. I'be betting that's what Chris has, although auto heat was an option for a cab in 1986. Either way, you turn the knob and the fans should come on.

JR

I love my car but even a yugo would blow cool air on the drivers face! But not my 85 Carrera! 27 fans and 14 levers and no cool air on my face! How did that happen? How did they make a $35000 car have terrible heating and A/C?

There's a thread somewhere on here which explains the circuitry for the footwell blowers very well, better than I am able to, but here's the overview:


The middle fuse of the 3-fuse panel behind the plastic cover in the engine compartment provides the power for the fan heating fan control unit, which is a plug-in device directly above it. The fan control module routes the 12V to the footwell blowers through the rotary switch between the seats. Here's the key to it all: The 12V for those routes through contacts of a relay in the module. The winding of this relay is in series with the engine compartment blower motor.The relay will NOT operate (and thus provide power to the footwell blowers) unless there is current flow operating the engine compartment blower. In normal operation, this means you must raise one or another of the red-knobbed levers between the seats, which provides the 12V to flow through the relay, onward to the rear blower, and back to the module to ground. In other words, any open in the circuit which powers the rear blower, fails the footwell auxillary blowers because the fan control relay won't activate.

In my case, I could raise the levers in the cabin and see 12V across the pins of the rear blower connector, but the rear blower was dead when it was plugged in. This placed the trouble in the rear blower motor. I removed it, opened the motor case in an attempt to repair it myself, and found that the entire plastic structure within it that holds the commutator brushes was burnt to a cinder. Replacement was the only option. When you think about it, that blower assembly is subject to a tremendous amount of heat over its lifetime, it amazes me that they last so long.

My recommendation: Open the engine compartment, switch the ignition on, raise the red-knobbed levers, listen to discern whether the rear blower motor is operating. If it isn't, pull the 2-pos. motor wire connector and meter betwen the pins. If Voltage is there, replace the motor. If Voltage isn't there, check fuse number two under the cover. If the fuse is good and has the 12V through it, you probably have a bad fan module. All the parts are available here.

Don

Cool air on your face comes from the A/C. If your car was built without A/C, you could get fresh air through the dash vents. If you've removed your A/C components, you can change what you have to allow fresh air to be ducted to the dash vents. It's been discussed here before, in detail.

Porsche's system seems complicated if you don't fully understand it. Most of the complaints come from people who don't have a good understanding of how it works and half of those have never even read the section in the owner's manual about how to use it. AND, there were several minor variations over the years, depending upon the market the car was built for, whether it had factory A/C and a few other things, so it helps to know something about the specific system in your car, and not what someone else has. And, if you've modified it, as many do, it helps to not just do "the removal" part and quit there.

Likewise, the heat is great, if everything works and it's adjusted properly. You can heat up the car much faster than a normal car.

JR

Have to agree with you, Nick. The idea of needing to read instructions how to operate a heating/cooling system is just baffling -- even as far back as the early 70s. Furthermore, to view heat/cold as a superficial excess speaks volumes about the engineering department's lack of total comprehension of automobile market. Luckily it took the Japanese to come up with the outrageous concept of "user friendly" and apply it to the automobile. So nowadays, anyone without all the creature comfort options that work easily and well, are immediately out of business.

It's like the preference for single-shot rifles over full automatics -- twenty-30 years ago, full auto was seen as a waste of bullets. NOT ONE soldier today will echo that ridiculous old idea.

There are two ways to look at it. What some people don't consider is that the system Porsche used gives you far more flexibilty than systems in other cars. Some of the BMW's had pretty decent controls that gave a lot of options to the user, but the 911 system was better in that respect. Modern systems are more user friendly but the climate control computer makes some assumptions about what you want and tries to give it to you. Sometimes that works, sometimes it doesn't. I can teach someone everything about a 911 system in about five minutes.

JR

Javadog, I did study the controls on my car. I know fresh air comes out of the defrost vents. . I know you can remove the A/C and re route stuff to get fresh air on your face. I know the heater works great. My point is that you should not have to do all of that stuff to get stinking air on your face. These are great cars but the heating and ventilation system is just stupid. So is the A/C. You can teach me everything about the 911 system in about 5 minutes but it still will not put cool air on my face when I am driving. That is the one main option I want.

A flexible duct under the ashtray coming from the A/C blower can direct plenty of air at your face or other body parts. Convection of even warm air has a cooling effect. The factory fan is plenty powerful.
Ice cold is overrated, except when prefacing the word "beer".

So, your A/C doesn't work?

JR

Yes my A/C system works fine. My point is that in a car like a Porsche if you want fresh air in the cabin or on your face you should not have to turn on A/C to have it. You should just pull a lever like any other car. VW had the right idea with old Bugs. Two simple levers for heat and defrost and a wing window for fresh air. Worked great on a trip!

If you want fresh air in the cabin, open the outside air vent and turn the blower fan on, if you want. You can use the A/C to blow cold air on your face.

Or, open a window, like in a bug.

Or, pipe fresh air to your center dash vents. There's a thread on Pelican on how to do it.

JR

Dredging up an old thread with a question - can anyone tell me why, with the levers set (apparently) correctly, I get warm air out of the passenger defrost vent, and cool/cold air out of the drivers defrost vent? Could it be a heat exchanger valve issue?

You might not be getting hot air into the left side of the car, back at the outlet from the heat exchangers. Or, the left side distribution box may not be directing the hot air properly, either because a cable is incorrectly adjusted, or there is something wrong with the box internally, or the small duct to the defrost vent is not connected.

JR

Thanks for the quick response - it gets cold being the driver.

For other searchers, I found the following article which is interesting:

Porsche 911 heating systems - Philip Raby Porsche

What year is the car? I assume you're getting no warm air at all on the left side? You want most of it to come out under the dash into the footwells, if you are cold while driving.

JR

I have an 83 SC with autoheat.... my problem is the fan in the engine compartment only runs on one speed. Should it not be 3 speed based upon the dial on the control box? and would it be a control box issue or a relay somewhere?
Basically the heat in mine works damn good even on real winter days in the NE

Is your '83 a cab? Do you have auto heat, or do you have the similar-looking box between the seats that has a control for fan speed?

JR

my 83 is a Targa w/autoheat. Just not sure if the 3 stage fan speed is regulated by the autoheat box or from ? a relay in the engine compartment

I think you only had a one speed fan. Porsche introduced a pair of footwell blowers on the '83 turbo, controlled by a switch on the dash to the right of the steeering wheel but I don't think the '83 SC targa had that. The later 911s got the footwell blowers and the autoheat control unit was different. There were 3 blowers speeds available, depending on the dial position.

JR