How does the heating system work for 74-89?

[RWebb]

Originally Posted by HarryD

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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'm glad you guys like the above post I wrote up. I don't recall where I first posted it - could have been PorscheFans, or the early text-only Rennlist.

[Va_Powerman]

Originally Posted by javadog

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

Yep, no warm air out of the left side at all - I've got the controls somewhat figured out. That's why I think it may be a problem somewhere in the heat exchanger duct and valve.

It's an '85 targa with auto heat...

[javadog]

Sounds like no heat is making it into the heater duct on the left side. First thing I'd check is if the hose on that side between the heat exchanger and flapper valve is missing or disconnected. A car with auto heat uses one cable that is folded in half and has a loop twisted into the end that attaches to the lever operated by the servo. Because of this, it can only pull on both flapper valves together. It's not unusual to have the flapper valves stick in one position, but the fact that there is only one cable half working indicates that the end of the cable on the left side might be broken, or loose in the little clamp.

It ought to be pretty obvious if you can crawl under the car and have a look.

In the meantime, move the red lever on the dash all the way to the left, the middle lever all the way to the right and the two upper levers all the way to the left. Crank the heat on but try to keep the footwell blowers at the low speed. So, maybe 1-3 on the dial.
JR

[Va_Powerman]

Yep, good call. The hose was disconnected...

Originally Posted by javadog

Sounds like no heat is making it into the heater duct on the left side. First thing I'd check is if the hose on that side between the heat exchanger and flapper valve is missing or disconnected. A car with auto heat uses one cable that is folded in half and has a loop twisted into the end that attaches to the lever operated by the servo. Because of this, it can only pull on both flapper valves together. It's not unusual to have the flapper valves stick in one position, but the fact that there is only one cable half working indicates that the end of the cable on the left side might be broken, or loose in the little clamp.

It ought to be pretty obvious if you can crawl under the car and have a look.

In the meantime, move the red lever on the dash all the way to the left, the middle lever all the way to the right and the two upper levers all the way to the left. Crank the heat on but try to keep the footwell blowers at the low speed. So, maybe 1-3 on the dial.
JR