Alan

H - thats because you live in Seattle... just comes with the territory - Oh and BTW you would't notice even if it did ... !

Alan

dr bob

My simple-cheap-easily reversible and foolproof proposal is to install a vacuum-to-open heater valve in series with the factory valve. Ford Escort valve IIRC, less than $20. Cut the hose between the existing valve and the heater core and slip the new valve in there. Connect the vacuum to the manifold connection that attaches to the FPR and dampers, NOT the one that supplies the flappy. Stop the engine, valve closes. Start the engine, valve opens. Downsidde is you might not have as much heat under hard acceleration when vacuum is scarce. Big deal. No wiring, no other mods, very easy to undo later. Just put a new hose in.

I have a Four Seasons #74614 valve on order to try. Will post pics and results when it goes in as part of my intake refresh project.

Alan

Roger - nothing much - the flappy valve and extra (short) vacuum lines a new vacuum 'T' for connection to the vacuum reservior and a flappy electrical connector.

Alan

heinrich

Alan ... Bob I like it. But
i really think my car holds vacuum after shutdown, will look to confirm.

Alan

H - sorry unless someone modified it it can't possibly.. but I''m serious you probably wouldn't notice...

Alan

dr bob

I can safely guarantee that it doesn't hold vacuum in the intake manifold. Trust me on this one.

Alan

Or in the hot water valve...

Alan

heinrich

Not questioningthat .. just questioningwhether the heater valve vacuum circuit is designed to lose vacuum from the factory.

Alan

All the console HVAC solenoid valves MUST lose vacuum when not activated or else turning them off would make no difference...! Its a direct functional requirement .

Alan

Stan.Shaw@Excell.Net

Please confirm the following, so I am sure I understand, then I can be confident of my testing.

The HVAC lower slide control determines which solenoid(s) to power.

When the ignition is off the solenoid opens to vent in atmospheric pressure.

When the engine is acting as a vacuum pump (cranking?) the position of the HVAC lower slide will determine which diaphragm circuit will be open to vacuum.

Thank you!

j.kenzie@sbcglobal.net

I was thinking about the rationale of the design of the normally open heater valve. In winter at shutdown, it leaves hot water in the heater core, so you can get heat faster if you resume heat after a short time. In summer at shutdown, the same hot water gives you a blast of hot air until the a/c evaporator cools it down. It occurred to me that the hot water in the a/c box might cut down on mold formation, since I never have had any odor problems that you can see with mold. The open heater valve would warm the evaporator and cut down on further condensation in the air box. Just an idea.

dr bob

The 'fail-open' configuration works in concert with a few other failure positions for actuators. Defrost vent fails open, comb flap fails closed, heatr valve fails open. So in a failed state, you have heat directed at the windscreen so you can see if it happens to be cold.

I propose adding a 'fail-open' heater valve in series with the original fail-open valve, but plumb the vacuum connnection to the intake manifold. That way, when the engine is running but not under high load/hard accelleration, the new valve will allow water to pass through. Shut the engine off, vacuum diappears and that valve goes shut at the same time that the fil-open factory valve goes open with no signal to the controlling solenoid. If you have a problem with your original valve, you can pull and plug the vacuum connection to the new valve and it will stay closed.

SeanR

How about when you have the AC cranked, you give the car 1/2 or more throttle and you get a huge blast of hot air slamming you in the face. I find that irritating. I would assume I'm losing vacuum.

the flyin' scotsman

Bob has it.............Porsche designed the car to fail safe in cold climates hence why ALL the vac valves when the lose pressure on time after shutdown open the way they do.

Manually closing the HWV in the summer months works well but thats assuming the valve seals; my solution was to have 2 HWV's; the old thats closed solid by tye wire and glue the new that works per design.

Ultimately I had thought about electric servos that would operate the valves and elliminate the vac system but haven't got there.............yet!

dr bob

Safe assumption.

The solenoids fro the five actuators have vacuum 'accumulated' (should be 'evacuated'...??) by manifold vacuum and isolated with the check valve. The HVAC system design protects the accumulator from bleeding too much thanks to small hoses and connections, so things like the vacuum cruise control, vacuum door locks, and on later cars things like the flappy actuator could continue to operate if there is a failure in the HVAC system. A leak in any of the systems in the HVAC will cause the pressure iin the system to rise, and the bigger the leak the shorter will be the time before other actuators run out of suction and move towards their 'failed' positions. Got a leaky comb flap diaphragm? Fresh air/recirc door actuator? Those are normally operated when the AC is engaged, and if they leak they will drag the heater valve alng with them.

The first thing to check is of course the little check valve itself. If it fails open, it will allow air to pass back into the accumulator when the engine is under higher load. It's pretty easy to test-- Pull the valve and see if it passes air in only one direction. A miti-vac is real handy for this, but you can generally blow through it wth your mouth in one direction only. Installed, it needs to pass air from the accessory side towards the engine side, and block airflow towards the accessories and accumulator.