ZEUS+

Seems like a lot of work, when just a switch and valve change will do.

borland

It's a hobby car..... its not about the work or expense. It's much easier to live with the 5 second hot air blast.

ZEUS+

Never bothered me !
A truly trick approach would be installing a BMW or Benz heater valve wired in with the setting motor.

TheoJ

Barry, the flappy solenoid closes the nose entry pretty nicely. So it keeps the vacuum on the warmwater valve when you shut down the ignition. The valve also has a bleed port (rear round black cap, you can see on the pic) and it can be left as is or closed. Closing is easy, as yoiu can take the plastic cap off. If you close the bleed port like I did, it works like a charm.
Eventually, after some time, the warmwatervalve will loose its vacuum due to minor leaks and will open. But by then the engine has cooled down and there is no reason to keep the warmwater valve closed.

borland

Thanks Theo!

Flappy Vacuum Solenoid Valve:
P/N Nomenclature
-------------------------------------
911.618.123.01 Vacuum Valve


HVAC Vacuum Solenoid:
P/N Nomenclature
-------------------------------------
928.573.691.02 Solenoid Valve


The electrical connector to the flappy part may be hard to source, while the HVAC part uses a common type blade connector.

TheoJ

you're welcome. So both valves will do the trick? Nice. Thanks for looking up the part numbers.

I was surprised to see that you had basically the same idea to get rid of the "unwanted heat syndrome". I appreciate all other efforts and modifications, but this modification is simple, keeps all functions operational, is reversable, and effective. What more can you ask for ??

regards

dprantl

Or you can just go down to a junkyard and pull a solenoid bank out of a 190E Benz for $2. I knew that would come in handy someday

Dan
'91 928GT S/C 475hp/460lb.ft

Alan

Theo - it isn't guaranteed to work. It will mostly work - but the hot water valve can be on in AC mode - if it is when you shutdown you won't close the water valve.

Whenever the AC has cooled the car enough - the way temperature is regulated is to open the watervalve and adjust the mixing flaps to warm the AC fed air slightly. The evaporator is always full cold in AC mode and all the air goes through it... the only way to be less cold is to partially mix heated air with it (not the most efficient - but thats how it works).

Essentially the AC on just reduces the temperature of the airfeed - temperature regulation works the same as it would be with ambient air of the same temp...

Alan

TheoJ

Alan,
true, if the AC would have switched on the heater (turned off the vacuum to the heater valve) then I'm still getting hot water into the heater core. It happens sometimes, although the effect of the little mod is good. It keeps a {closed} warmwater valve closed for a long time.

In the USA you use the AC probably a lot more then we do in the Netherlands. If you want to fix that AC-heat-on state also, you could connect the rear side of the valve (bleed side ) to the vacuum booster. I think that is what Barry already mentioned. There is a convenient hose connection if you take the rear-side cap off the solenoid. The new connection will put vacuum on the heatervalve when you turn off the ignition. I'd need to check but I think it won't cripple the normal operation as it seals off the bleed side when 12v is on the solenoid, and connects the heatervalve to the HVAC solenoid assembly.

Alan

Theo - yes, exactly. The flappy solenoid valve seems to be the way to go here since it can more easily be used as a true 3 port valve (rather than to 2 port with bleed of the HVAC solenoids) - thanks for that info. Still considering all the options.

Alan

Alan

OK I've been pondering this and I think I'm going to implement the Theo vacuum route with the stock water valve using the flappy solenoid valve with the vaccuum reservoir plumbed to its vent port.

(sounds a bit like Colonel Mustard in the library with the lead pipe...)

My reasons are that after consideration there are 2-3 downsides to what I proposed with the default closed hot water valve.

1) Filling the car with coolant with the ignition off would be complicated by the closed water valve and mechanics working on the car would not know this.

2) If the HVAC should loose vacuum in the winter you would be without ANY heating - I'm sure this was a Porsche consideration in choosing the default state - not just for engine off but also for vac loss.

With the stock valve and no vacuum you'd have good heating and functional but compromised AC cooling.

3) Adding an ignition controlled solenoid is far easier than adding a function reversing relay. The failure mode of the solenoid is also to default to heat - while the failure mode of the relay would be default to no heat.

For me working though this makes it clear which path to take. The flappy solenoid is already rated for engine compartment use - thats where it lives. I will install the solenoid in the bulkhead area and then the vacuum reservoir feed is also very easy. I already have used the firewall grommet near the wiper motor - so thats easy too.

This was a great discussion and changed my thinking here quite a bit - this is probably a cheaper and easier to implement solution to this issue - and easy to return to stock behaviour too. I think I'd recommend it to anyone who lives somewhere really hot - however I'll implement it before saying more...

Big thanks to Borland for this idea - a very good one - and the solenoid part # and to Theo for both the same idea and implementation details...

Alan

the flyin' scotsman

Always liked Miss Scarlet myself

Let us know how it all works Alan............pics would be nice

robot808

Alan,
In a recent post you said to me, "and you know the lengths I will go to if I think its worthwhile...."

You ain't just whistling Dixie brother.

borland

Alan,

I’ve found this three-way vacuum solenoid valve on eBay. Its is Mercedes part number 001 540 70 97. Described as a EGR actuator solenoid valve.





You can see in the second photo the rubber vent has a plastic insert with screen.

There are several of these on eBay. Search “Mercedes EGR Valve” and look for the solenoids. About $16 with shipping. Make sure you ask the seller for a electrical connector and pigtail.

It functions exactly the same as the flappy solenoid valve. I did some tests with my Mity-Vac. Here’s the results:

Coil Un-energized:
1. Vacuum at actuator port (3) - draws air from vent port (1)
2. Plugged at actuator port (3) - draws vacuum from vent port (1)
3. Vacuum at vacuum port (2) – holds vacuum at vacuum port (2)
Coil Energized:
1. Vacuum at vacuum port (2) – draws vacuum at actuator port (3)
2. Vacuum at actuator port (3) – draws air from vacuum port (2)
3. Vacuum at vent port (1) – holds vacuum at vent port (1)

Do you think this will work?

I think it might be easier to install behind the center console to reduce the vacuum line lengths, but where would you find ignition 12v power available some where in the engine bay?

SharkSkin

Alan, this cropped up in another thread recently... did you see Bob's automagic solution, posts #17 & #27 here?