ZEUS+

It's actually quick and simple, all under the hood. As long as there is room like you stated. Just a suggestion. Dont suffer from the extreme heat up here.

Alan

I do think room is a problem - took a look.

To your original proposal (before edit) since the HVAC reservior vacuum is maintained for some time after shutdown and the solenoid valves bleed-off immediately downstream after powering off - there is still a period where both would be open - eventually it would close.

With the (edit for) extra solenoid valve so it also bleeds immediately - yes works fine - but now we have to add an extra solenoid valve & vac line through the firewall (or a solenoid valve in engine compartment?).

Given that - I'm still interested in Borland's idea - its a new twist - all local to the HVAC - no new vac lines to route through the firewall (just locally looped to the extra solenoid valve) and keeps the single stock water valve.

I'm thinking that a test mode for this would be to plug the water valve solenoid's vent port and see if it holds vacuum after shutdown - I can run this way for a while (summer) and see if the heater core stays cool or not after shutdown. If it does then add the extra valve as proposed...

In this test mode I loose all heating and temp regulation BUT its a good proof it can work before getting the extra solenoid valve. Then if it works I think I'll try to locate a 6 way '83 valve/manifold set as a swap. (Anyone got one sitting around...?)

Alan

rssmith

I knew I should have kept the box. The valve I have is labeled H36-1200-047, but I cannot find that number in the NAPA web lookup. I searched the site and the one that looks the closest is Balkamp Part: BK 6601024. I lied about the valve being metal, but now that I think back I believe I had brought home 2 or 3and returned the ones I didn't like.

It has been working nicely and it was a relatively easy process. To qualify relatively a little, the hose sizes are not right on. I could not find anything with the differing input and output hose sizes that our OEM valves have so I ended up converting to 5/8 on both sides. It eliminates the small failsafe hose, but debate on the need for that has been around for a long time. I have a couple of pictures of the installed valve, the valve from NAPA and the relay mounting in the control head. The blue hose is silicone heater hose which is super high temp hose and for my purposes VERY flexible compared to the stock preformed butyl rubber. That made the tight corners and the off size fittings work out easier.

RSS

Alan

Another thought here for Borland's extra solenoid valve to maintain valve vacuum idea...

In normal temperature regulation AC mode the water valve may cycle on & off (along w/ mixing flaps movement) as needed to regulate temperature (even at below ambient temps ).

So the only way to be sure the water valve is off when you shutdown (so you can maintain that state on the water valve) - is to slide the temperature slider to the MAX cooling (microswitch) mode just before shutting down.

Typically if you have not yet reached any set temp in AC mode the water valve will indeed be closed - but once you have achieved that temp and are in temperature regulation mode the water valve is just as likely to be open...

Alan

borland

Interesting Alan,

Well since it's a three-way valve, instead of capping the port, you might be able to run the 'bleed port' to the vacuum reservoir. That way when the ignition is switched to "off", the heater valve actuator would surely operate to shut coolant flow off, regardless current state.

It's been a while since I last looked at the valve, but I think it might be possible to install a third hose connection. I did replace a defective one on my 90' S4, but that was several years ago, and I recall the three screws that hold the valve mounting rack are difficult to reach.

Alan

Have any idea how well the vacuum reservoir holds vacuum after shutdown? - seems operationally it really only needs to hold vac for a few mins to stablize engine vac fluctuations... is it in practice much better than that?

Alan

dprantl

Unless you have a vacuum leak, I would think the reservoir will hold vacuum indefinitely. Recently I did some testing on my car after it was off for over 24 hours and when I disconnected the line from the blue/black check valve, there was still a large amount of air being sucked into the reservoir.

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

borland

Looks like it might be a challenge attaching a vac hose to the vent 'M'.

ZEUS+

Just another suggestion. Normally closed heater valve, vacuum solenoid and switch. 1 wire to run. Can be done in vehicle or under hood. With older vacuum distribution unit(more work) or another solenoid(much easier). Or use switch to control existing solenoid(easiest). We push a button for AC, same thing for this.

TheoJ

I noticed the discussion and Borland's idea. Barry, you almost suggested what I did on my 928.

What I did is just cut the vacuum line between the HVAC solenoid bank under the center console and the warmwater valve. I put a solenoid from the flappy control in between ( the one like in front of the driver.side head, bleed side closed).
When I turn on ignition, the solenoid opens, and connects the warm water valve with the HVAC bank, allowing normal operation. When the engine is hot and I turn it off, the 12v drops and closes the vacuum line, thus keeping vacuum on it for a long time. It effectively keeps the warm water valve closed if it was closed. Typically in the summer. That prevents unwanted hot water entering the system. Easy fix, no crippled operation and low cost
It can even be reversed bu just reconnecting the cut vacuum lines with a rubber connector tube.
regards

F451

This idea sounds the best to my uneducated and now pretzeled brain from trying to follow all of this.

Theo, any chance you can post some pics? Or will it be pretty obvious once I consult the manual and get under there?

TheoJ

hang on, Ed, I will try to make a diagram tomorrow and post it.

borland

So we have it tested already and seems to work. But Theo... Alan says the hot water (heater) valve could be open with the AC operating, so running a bleed port to the vacuum reservoir was considered.

Well the Porsche Service Tech info for 87 S4 doesn't say, but it likely has a bleed port too.


Connecting a line to the vent ports on the solenoid vacuum valve is easily done, but I need a test solenoid to test the valves ability to work this way. Flappy solenoid is probably the same design, just different arrangement of ports.

ZEUS+

Wouldnt a switch to control the existing heater valve solenoid with a normally closed heater valve be simple and effective ? Switch off, no coolant flow. Switch on, coolant flow.

borland

A simple NC (normally closed) SPDT relay is all that's required to reverse the operation of the HVAC vacuum solenoid valve, so yes using a normally closed heater valve would work. Just a different approach.