rcoble

I don’t know if anyone has done this before but this is my solution for the heater valve being on when the car is off, and thus making it hot as hell when you return to the car after a short stop. This is a bigger deal for those of us who have not fixed, or are missing parts of their AC.
I first modified the heater valve so that when vacuum is present the hot water is ON instead of OFF. Just made a new L shaped bracket for the actuator so it hooked to the valve in the opposite direction.
Then used a simple sealed relay from radio shack to reverse the power signal to the vacuum switch for the heater valve (behind the center console) so that it gets power when the heat should be ON, Instead of the when the heat should be Off.
Now heater works normaly, but the new default (when the car power is off) is NO HEAT!
Robert

OK as promised here is a diagram (CG That I did) for how to modify the heater valve:

This is what a heater valve looks like in the default open position.

This is the bracket you will have to make.

This is how it ataches (not showing screws and glue)

Move the actuator to the new mount.

Make an extension for the actuator arm (shown in green). Make sure there is a little pressure on the valve so it will be tightly closed.

Next, the relay picts ... stay tuned.

Here it is:

Robert

bd0nalds0n

That's interesting; I was going to add a second heater control valve that needs vacuum to open. Start the car, the 2nd valve opens; shut off the car, the 2nd valve shuts. No more hot water circulating when you shut off the car. My climate control works okay otherwise.

How did you modify the heater valve to reverse its action?

rcoble

Not really too hard to modify the valve, just cut a peice of sheet aluminum put a 90deg bend in it cut and drill some holes. Glue and screw it to the old mount.

Flott Leben

Just curious, how would the coolant circulate when the car is shut off?

I assume the 928 system was designed this way for a reason - maybe to always have coolant circulating through the heater core to avoid rust or deposit buildups? Or maybe to help dissipate heat since these engines run so hot anyway? Anyone?

bd0nalds0n

Well, it stops "circulating" when the water pump stops.

However, the "failure" mode for the climate control system is a) heater valve open and b) defroster vent open. Hans wanted to be sure that if your vacuum system fails while you're cruising thru the Alps in a snowstorm, you won't get a frosty windshield.

As a practical reality of the above, when our cars are shut off, the heater valve opens. This allows the hot water that was heretofore prevented from mixing with the heater-core water to commingle, thereby transferring heat to the interior of the car. If you start the car before the temp is back down, you get a blast of hot air.

There have been various workarounds advanced over the years--unsurprisingly, they tend to orignate from the southwest US, some crude, some elegant.

rcoble

True, the water pump is not running when you turn off the car, but when the car is off the heater/water valve opens allowing water to circulate slowly due to expanding water stuck in the engine etc. Then when you turn the car back on the heater core is quite hot, trust me on this one, I don't have AC. Other people have modified their heater valves in the summer by tying the valve shut.

Alan

I think the default configuration makes sense if the predominant conditions where you live are cold. In the case of Germany - most of the time its a benefit to have some prewarmed water in the heat exchanger so you get faster warmth when you resart after a short stop.. If you live somewhere where its predominantly hot (like Phoenix!! the opposite is definitely true).

You could argue a case for a conditional valve that opens on shutdown only in the wintertime (based on external temperature). But as a vacuum valve it has to have a single default direction... I guess if I lived in Germany I'd choose the same thing...

I doubt it has any effect on the engine cooling...but maybe its helpful to circulate the heater core water from time to time when the AC is left on - but I doubt there is enough flow to flush much with the pump shutdown...

Alan

borland

Good job. I thought about fixing this in two other ways without changing the heater valve.

1. Install a second vacuum solenoid valve (modified by plugging the bleed off when power is cut) in line with the heater valve actuator. Wire the second vacuum actuator so it is powered (open) with ignition on. So when the ignition is turned OFF and the heater valve is closed, it stays closed.

2. A simple timer that senses the ignition is turned OFF and continues to supplies power to the vacuum solenoid valve for a period of time, maintaining the heater valve in the closed position until the timer expires. Course the timer would also need to be inactive during ignition ON.

Flott Leben

Gotcha. I was just wondering if the water circulates after shutoff due to gravity, pressure in the system, etc. I didn't know.

So, when the engine starts up, the valve to the heater is closed with vacuum and then only reopened when the climate control triggers that heat is necessary for the inside cabin? In other words, default when engine running is closed and default when engine is off is open? Or am I completely off base? Thanks.

rcoble

Yes you are right.
Except I don't know if I would call it a default to be off when the engine is running. Thats not really a default. The valve will got to the state requested by you via your climate controll settings.

heinrich

please post a step-by-step so Homer Simpson and I can follow it.

rcoble

I knew someone would need the pictures I didn't take. So wait a bit and I'll CG the steps.
Robert

rcoble

Ok I added some picts to the original post.
Robert

Randy V

Nice CAD work!

chaadster

Nice work Robert, both on the mod and the CG graphics!