heinrich

Speaking of which, I've always thought that a simple 1972 Mazda pushrod cable to a simple push-closed pull-open heater valve would have been a MUCH better option than all those stupid vacuum hoses and solenoids. One cable for heat, one for open flaps, one for close flaps. DONE.

Bilal928S4

Isn't that how the old beetles and 911 were set up?
Bilal

JPTL

After the original plastic valve's seal came loose letting by a steady flow of hot, I tried various aftermarket valves & eventually a petcock. On a hunch that when working correctly, the oem valve would close off the flow 100%, I went back to an oem valve a few months ago. Although it works much better than the original & the aftermarket vacuum valves, it still doesn't close off the flow 100%.
I can't assume that it's the valve. I have to gather that I have a small leak in my vacuum line somewhere.
I therefore agree with MainePorsche who says the right approach is to test for a vacuum leak.
..but I also agree with Heinrich. A vacuum system has vulnerabilities whereas a simple 'on/off' valve is bulletproof.
I'm therefore considering using both valves which will take less time than vacuum diagnosis/repair:

• OEM valve installed in its original position & connected to the vacuum line
• Petcock spliced in the line along the firewall.

With this black car in the hot DC Summers, I need all the cooling that my AC can muster. The tiniest bit of hot water getting to the heater core competes with the AC and it becomes inefficient. So, in the Summer, the petcock would be closed and completely seal off the hot water that's apparently getting by the oem valve.
In the Fall, the petcock is opened and is essentially 'disabled'. The oem valve takes over for cooler/cold weather and the vacuum temp. control goes back in use.

Alan

H - I believe some very early (heater only) cars were set up exactly like that stock...

Personally I continue to use the stock valve - mostly they seem to be OK - need periodic replacement - but I expect all types will.

I do have a planned modification for the hot air blast on restart, an additional vacuum solenoid in the heater valve vac line. Its a flappy solenoid - engaged with ignition to be open. It closes as soon as the ignition goes off and has its vent connection plugged. This will always turn on after the HVAC and turn off before the HVAC (HVAC is X-Bus - accessory - driven).

The extra vac solenoid will hold whatever was on the heater valve (vac or not from the head unit) after the power goes off until vac leaks away at the actuator. This means the heater valve can basically practically default either way depending on what the HVAC head was commanding when the car was turned off. If you were in heating mode it will say open if you were in full cold mode it will stay closed for quite a long time (and based only on leakage on the heater actuator diaphragm).

I have not installed this yet - but I believe it will work fine. Of course the system has to be functional and the valve seal effectively - mine seems quite OK in those respects.

For those of you with permanently off water valves: petcock, wired shut - whatever... you do realize you now really have no temperature control at all...?

In AC mode the AC is always on (unless the evap freezes) and the only way temperature is controlled is by opening the water valve and mixing. Without the ability to open the water valve the only way to regulate temperature is with the blower fan and AC switch - e.g. modulate AC on/off and or reduce the air flow (maybe recirc/vs fresh too) - in any case very manual.

If the system is working effectively the AC should eventually get you uncomfortably cold air blowing on you - it certainly does for me even in Phoenix in summer - it may take a while - but on a long trip and especially out of town - I'd eventually want to be able to warm up that airflow to a comfortable temp. So for me a permanantly closed valve just wouldn't be a good idea.

Alan

JPTL

Bilal, air cooled cars had a different system I believe.
Water cooled cars & trucks 40+ years ago had slide controls that were basically cable operated petcocks.

Imo000

Even the early 90's Civics had a cable oprated controllers and they were buletproof. Then they switched to electric servo motorsm and they were also very robust. The vacumme controlled units, doesn't matter the make, are always the most vonurable for faliure and over time they ALL will fail. Rubber only lasts so long.

heinrich

Agreed

BC

So we need to find an electric valve.

heinrich

agreed.

heinrich

http://shop.advanceautoparts.com/1/1...art-74852.html

heinrich

agreed.

ROG100

I use an early manual heater valve for a 924. It allows manual operation which here in Texas is about twice a year. A customer of mine in Australia came up with the idea of plumbing the manual valve after the stock vacuum operated valve so that in the winter you could still have heat and cold.
A small length of wire to the manual valve allows you to make the change without removing anything. I found the closing of the vaccum valve using tie wraps or whatever a PITA.

Imo000

Got the valve, intalled it and works as it should. However the NAPA Canada part number for a '92 Caravan, without aux heater, is totally different (H6332) and only the plastic version is available. The auxilary heater model has two outlets. The in/outlet pipes on the valve are slightly smaller than the Porsche part so the hose clamps had to be crancked down a little more. The short hose and the long heater hose were already replaced by the PO and look pretty new so I didn't change them.

Here is what the part number and the part from the Canadian NAPA looks like:

Jim Devine

I think this is what Roger is referring to- it's an exact
fit- just uses a cable. If you don't want/ need the blend
feature of the vacuum one this should do it.

http://www.autopartsnetwork.com/imag...1630166TKU.JPG

ROG100

I should of mentioned that Jim turned me on the manual valve a while back - thanks again Jim.