Constant blowing heat...

[Kenda11]

Looking for a little guidance on where to start in eliminating annoying blowing heat the comes from under the dash on the passenger side of my 76' 911. I also could not stop the defrost from blowing. Interim fix for that was to pull the #2 rear fuse. What seamed odd is that the defrost blowing out of the driver side vent was ambient air temperature where the passenger side clearly was relative to engine temp. This heat is constantly present and seams to increase blowing when moving. None the less, It's not much fun to drive with full heat on in the summer...Well, it's fun until the engine warms up.

This all started after my local repair shop replaced the intake seal. I don't think the repair is related, however this is my point of reference. They are willing to look at it. My problem is that every time I drop it off they have it for 4 to 8 weeks. I could live with it and drop it off this winter, but I thought I'd give the forum a try.

Thanks!

[javadog]

First, you need to find a new shop. Any shop that keeps your car that long for a repair is not worth using.

Put the fuse back in, that's not your biggest problem. The valve that directs heated air from your heat exchangers into the right side of your car is stuck in one position. Do a search in this forum for the specifics of where it is and how to fix it.

While you are at it, search also for how the whole system works, so you can sort out the other problem you have. Once you understand what all of the components do, sorting this out yourself won't take you long.

JR

[porschenut]

It sure sounds like the right flapper box is stuck closed, directing heat into the cabin instead of exiting to the outside. It's a common problem in older cars as the flapper boxes get corroded and finicky. The left one appears to be fine.

[Jdub]

Your setup may differ slightly from my '78 but here goes.. First, do perform a Search on Flapper Box to begin understanding how the heat works.

The system is a bit lame - engine heat is blown through a pair of large hoses you will see when you look at your engine. You decide to allow all part of the heat in using the pair of levers between your seats. Full up is full on, full down is full off. If all is working as it should, the moment you lift either lever, the heater blower motor is grounded and begins to blow through the hoses, augmenting what is arguably an MG-grade system.

Problems arise when the wires to the flapper boxes that allow/prevent heat to the cabin break or become sticky, and when the actual rounded cap plates on the flapper boxes decide to rust to their pivot pin. Now, you have a permanant heat on or off depending on the state of the cap plate. Next, the blower motor often will not work because the switch under the levers, which is plastic, degrades over time and finally packs it in. Finally, that same blower motor in the engine bay (look upper left) will often pack it in or worse, run and melt the wiring at worst.

You are getting alternate heat - sounds like one flapper box is not dumping the heat but instead is driving it to the cabin. Compounding this is the fact it *appears* there the heat is blowing in - sounds a bit like the blower motor is on all the time, but noshing is simple - it could easily just be how fast your engine is running. You see, the heater blower motor augments the flow of air, but frankly many find that, at higher revs, they are getting plenty of heat since the fan in the engine forces hot air through depending on the speed of the engine. They decide the blower motor is not needed and pull it totally. This is referred to as a "Heater Backdate" for our cars, since it makes them work much as the older Pcars (and your old VW).

So get the car on a lift in a GOOD PORSCHE SHOP FOR GOD'S SAKE and have a look.

[boss11]

+1 on sticky flapper box. Jack up one side reach in there and open the box by hand. Don't play with the leavers between the seats and it will stay open. Spray some crc/wd40 if it wont budge.

I had same issue on drivers side, my feet were getting roasted in summer. Opened the flapper box by hand and no more hot air inside and I can still use my levers to close the boxes if I want, it just won't return to fully open position afterwards.

[megerian]

unwanted heat

[sugarwood]

Is this how it works? The default position is for the flapper box vents to be open. This allows hot air to escape outside. When the lever is pulled up, the flapper box valves close, and air is directed into the cabin. The red lever also closes the heater blower circuit.

If the flapper valve was stuck open, wouldn't the red levers also be stuck? If not, doesn't that mean the cable is broken? I don't see how it's just a case of lubing the flapper box.

[javadog]

No, and no. Have a look at how the cable attaches.

JR

[DRACO A5OG]

Originally Posted by sugarwood

Is this how it works? The default position is for the flapper box vents to be open. This allows hot air to escape outside. When the lever is pulled up, the flapper box valves close, and air is directed into the cabin. The red lever also closes the heater blower circuit.

If the flapper valve was stuck open, wouldn't the red levers also be stuck? If not, doesn't that mean the cable is broken? I don't see how it's just a case of lubing the flapper box.

Default would be lever down and flapper vent closed but re-direct ports open.

If flapper vent is in open position and levers do nothing then the cable is most likely broken or came off the fastener at the box.

Lube is part of it but sometimes the cable stretches and does not fully close the flapper.

One has to get under the car and ask a helper to raise and lower the levers and and observe the flappers. Up the ports are closed and vent is open and heater motor should be running, if with foot blowers those will run too.

Lever down the ports are open ( ports I mean the three triangular holes ) vent is closed, heater motor should be off.

[javadog]

The flaps on the boxes are spring loaded, so if a cable fails for some reason, the box should close the air supply to the cabin. The usual reason that they don't is that the boxes are rusted.

All of this discussion is taking longer than just crawling under the car and looking at the box. The problem will be immediately obvious.

JR

[javadog]

[DRACO A5OG]

+1 get under the car and see what is going on

[Bob Kontak]

Originally Posted by Kenda11

This all started after my local repair shop replaced the intake seal...............they have it for 4 to 8 weeks.

It rained in the NE for about six straight weeks this early summer. Damp. Your boxes, outside at the shop, could have rusted a wee bit more allowing it to freeze up?

This does not sound terminal if it's just a few months extra corrosion.

Use jack stands. If you don't know where to place them or where to lift, just ask.