Earl Gillstrom

When you shut the engine off, the heater valve
opens and hot water from the engine migrates into
the heater core. If you restart the car after a short time, you have to cool that hot water
before you get cool air from the vents.

If you want to circumvent this problem. see the
writeup by Gary Knox on my website.

It takes less than half an hour and is reversable
to stock operation in less than a minute.

<a href="http://members.rennlist.com/captearlg" target="_blank">http://members.rennlist.com/captearlg</a>

Mitch Johnson

Great idea, simple, workable, and easily reversable solution.

Thanks!!

Jfrahm

You can buy a 3/4" manual heater valve also, what would happen if you installed one in the return line at the water pump on the front of the engine? It would be easy enough to open and close when you wanted to, and would also not fail open at the wrong time. It'd be easy to mount and work with right up front and center like that too.

-Joel

P.S. I suppose you could also put in a cable operated heater valve and hide the cable pull under the dash. There are lots of cable valves in old VW, Honda, US-made cars, etc. Some of them are probably 3/4." This would be good for me, as I find myself in the cold, high mountains and blistering heat on the same day.

Earl Gillstrom

Joel,

It would probably be easier to use a vacuum "Y" valve and Gary's modification if you want control from inside the cabin.

Keep in mind that this modification is probably not necessary for your application. Leave it stock, when you know you will need heat. Or do the mod and flip open the hood for 10 seconds to do the switch.

Jfrahm

Since my heater valve is bad, and I cannot easily replace it right now, I went ahead and put a manual valve on the return line. This is a cheap, easily reversable modification which should also prevent hot coolant from entering the heater core every time I shut off the car:

<a href="http://boards.rennlist.com/upload/valve.jpg" target="_blank">http://boards.rennlist.com/upload/valve.jpg</a>

I got a stub of 3/4" heater hose and connected it to the 'hard' return line before the rubber line to the water pump. It would be nice to put that valve closer to the water pump, but that rubber line bells out before it connects to the water pump and I'm loath to cut into it.

Here is the part number for the 3/4" manual water valve:

Factory Air Corporation #84707
Autozone part #142943

It's $8.99 at my local.

Once I fix the heater valve I might consider a more elegant vacuum operated mod, or a cable operated water valve for summer/winter changeover inside the cabin. A small vacuum ball valve I could reach from the driver's seat might do the trick.

-Joel.

Old & New

Elegant solution:

(1) put an electric solenoid vacuum switch in the heater valve vacuum line.

(2) wire the solenoid valve to shut off when the ignition is off.

Heater valve stays in current position when ignition is switched off.

WallyP

A more radical solution might be to fix the vacuum system so that it works as Porsche intended.

If you replace or block off any leaking vacuum actuators, repair or replace any leaking vacuum lines and fittings, and clean/replace the vacuum check valves, the system should hold vacuum for much longer than required for the engine to cool off - end of problem.

Jfrahm

I was wondering about that... if the vacuum was really supposed to drop with the car shut off or if the HVAC system would still be running off of the vacuum reservoir for some time as one would expect.

-Joel.

Old & New

The way Earl was talking had me thinking it was *supposed* to behave that way.

This thread is giving me Deja Vu a La 50 previous posts on the topic!

Alan

OK someone linked to this (old old old) thread and I saw this answer. Unfortunately its just wrong - even if the vacuum system works perfectly the heater valve still opens after the ignition is off. This is the way Porsche designed it. The heater valve is controlled by a solenoid valve that turns off when he ignition is off. When off the downstream side bleeds off vacuum quickly through a vent port & the water valve opens.

Alan

j.kenzie@sbcglobal.net

I absolutely agree. On the other hand, a normally closed vacuum solenoid in line with the heater valve and wired to an ignition voltage would preserve all essential function and keep hot water from entering the heater core until the car is started and the heater valve is asked to open.

Alan

Unfortunately also not true - since the heater valve may be open when you shutdown - even in cooling mode. If the car has already reached its set temperateure in the cabin - the heater valve is likely to be open for temperature regulation. In this mode you still want the heater valve to close on shutdown so the heater core will cool (it will much faster than the engine block).

So what you need is a 3 way solenoid valve (like the flappy valve) that is controled by ignition to connect the valve to the solenoid with ignition on and the valve to the vacuum reservoir when the ignition is off.

Alan

j.kenzie@sbcglobal.net

You're so smart, Alan. That's a great idea. I wonder how to make it work.

ROG100

I feel a "hot climate" kit in my near future.
I can get the new 3 way valve - what else do we need Alan.
Roger

heinrich

For the record, my heater valve does not warm up when the car is shut off.