I agree. I top quality window tint would be a huge help. I will consider. Have gone that route on other cars with decent results. I always use a windshield sunshade when parked. But tint would help all the time.
Thanks,
Dave

 

Leave to go do some work and look what happens....

I love you all, and mean no disrespect or hurty-feelers.


-- The "normal operation" we see on engine shutdown is due to the failure mode defined during design. Everything defaults to a winter needs-heat condition on engine stop or when there's nothing driving any of the actuators. Electrical fail, vacuum fail, whatever - - you get heat on the windscreen and some to the footwells, and a little to the center and door vents for defogging. This was done intentionally. The byproduct of that thinking isn't kind to folks in black 928's in Phoenix or anywhere else where summer temps exceed 70ºF.

Virtually everything we are discussing now is a possible hack to get around some of the default actions that are essential parts of the failure-mode part of the original design. Zip-tie the heater valve closed when it's not winter and the issue is taken care of. Add another valve to isolate the heater core when the engine is off. Add another vacuum solenoid to block the factory heater valve while the engine is off. Manual or automatic valves, it makes no difference really; your intent is to block coolant flow at all times during the summer, engine running or not. All change the failed mode to equal no coolant flow through the heater core.


Choose the description you prefer. I don't care. While you ponder the benefits and costs of doing any of these steps to block coolant flow to the heater core at all times all summer engine on or off, grab a cable tie and your 10mm socket, lift the air cleaner housing, and zio-tie the damn heater valve closed. Then, before it gets cold again in a few months, you can brainstorm the improved versions under discussion.

 

Thanks Dr. Bob.
The nice thing about the NC vacuum solenoid valve is that is locks the heater valve in whatever state it is in, at the time of electrical shutoff. Then when the ignition is switch back on, the valve opens and returns control to the factory system. In the Summer, the closed valve would stay closed after shutoff. In the Winter, the valve would be open and stay open after shutoff. With the ignition on, the valve essentially disappears. I got the valve today and am waiting on hose barbs, but expect it to work pretty well. Plus it's totally no-touch, once installed. I will report.
Dave

 

Dr Bob,
You aren't thinking this through... You can HAVE IT ALL - the fail safe and more logical operation are not mutually exclusive.

Alan

 

Alan, I've thought it through very completely. Any fail-safe mode that includes heat when no actuators move (failure mode) will give you heat when no actuators move. That's why I've described it as "failure mode". It's a design feature. It's sometimes an inconvenient design feature I know; I lived in Los Angeles where it's "only" 100º a month or two of the year rather than all-but winter where you are. Black car with no tint. I get it. It's hot. Too bad for us the engineers from northern Europe decided that heat was the preferred failure mode.

High temp today was in the high 60's, Will be mid 70's tomorrow, high 70's by Thursday at dinnertime.

 

Hi Dr. Bob,
Everything you said is correct, but the action of "failure mode" or fail-safe mode could be to return to or retain the most recently selected state, whether heat or no heat. A cable-actuated heater valve could do just that. There should be an electrical/pneumatic analog that is similar. I don't know, but I'm working on something. The NC solenoid on the heater valve control line should do that pretty much.
Thanks,
Dave

 

Really - how is tying the heater valve closed or adding a manual valve any less of a fail safe defeat? A simple manual override is available for this mode too and you'd only ever need to use it in case of failure - not every single time the weather gets colder. I have an extra flappy solenoid on the back of the bulkhead (easily accessible drivers side ) with a plug in the short hose on the "sealed port". In the unlikely event the flappy solenoid fails to open I can just swap the vac hoses and revert to stock (including failed) operation, or pull the plug for always heat. Never had any issues with this updated config over the last ~5 years - it makes the car much nicer to daily drive. In my 22 years of ownership the stock flappy has always worked and the HVAC never had an electrical or vacuum failure. Meanwhile the weather changed many many times a year even in Phoenix - AND still most of every year was Hot Hot Hot. Bit of a no-brainer for me.Of course it never gets cold enough here that failure would ever become more than a slight comfort issue - but I'm prepared for it elsewhere anyway. But YMMV!

High temp today was 111F. For the next 14 days the lowest high will be 107F and the highest 117F. Mostly above 110F. So ask me why I care?

Alan

 

Hi Alan,
I guess what I meant was that coolant is actively circulated by the water pump for the first few seconds after startup, thus filling the heater core with fresh, hot engine coolant. The heater core will warm by convective circulation at a much slower rate, but could still be very effective, depending on the time between engine startups. As you point out elsewhere here, 8 hours in the sun makes all of this irrelevant, because the entire car will heat up to ambient temp or above, due to heat trapping.
I completely agree that in all situations, a heater valve that retains its state at time of engine shutdown would be desirable, and never really a detriment.
Thanks,
Dave

 

I think this sums-up and accurately describes the preferred behavior succinctly.

 

So, I got all my hardware for my NC vacuum solenoid system. I wired an ignition-switched 12V NC solenoid, and placed it in the vacuum line to the heater control valve. The first picture shows the general arrangement before mounting.
The second picture shows the heater valve open with the controls in the full hot position.
Third picture shows the heater valve closed 3 hours after engine shutdown from full cold AC position.



Since this is vacuum based, it should work with any properly functioning heat valve.
Thanks,
Dave

 

Dr Bob's point is it will work fine until the new solenoid fails and doesn't open.

I used a flappy vacuum solenoid but its functionally the same as yours (is yours rated for engine heat?) Do you also have another sealed port on that valve? (e.g. a plugged NO port) if so adding a simple ball valve there gets you an always open water valve if the solenoid fails (so just a twist)

I do get Dr Bob's point - However 2 things:

1) The fix for the solenoid failing is even easier than having to untie a closed stock valve - since it (or even a remote ball valve) can be placed somewhere quite convenient. (e.g. just loosen a hose connection or open a ball valve)

2) If it fails in winter you'd always get heat anyway, it if fails in summer you'll get better cooling as long as the vacuum holds (which could be quite a long time). Then its much less bad than an AC failure. Swapping the hoses on the flappy valve restores normal operation if the HVAC is otherwise fine.

My feeling then (and still now) is that this is much better functionality (for me) with very minimal downsides, certainly no safety ones. I have no plans to sell the car (ever really) but if I did I would take it off - its very very easy to revert to stock operation.

Alan

 

Alright, you are correct, Alan.
I don't think my solenoid will work for two reasons. One is engine heat. It's rated for 176 d.F, but I don't think that's enough. The second is time delay. The solenoid opens immediately when power is applied from ignition. The valve opens, but the car has lost some vacuum and it takes maybe 10 seconds before the valve which has quickly opened, pumps itself closed again. During that time the engine pumps hot coolant through the heater core. I have thought of combining Gary Knox's mod with the solenoid, but heat is still a problem. I think I will go back to stock, with the addition of my wrench for Summer months. I know it's a kludge, but it seems to work. I may look for a place to put a ball valve, but my supercharger piping takes a lot of access away from me.
Thanks again,
Dave

 

Well, I'm pretty disgusted. Naturally a/c work takes place in hot weather over a hot engine. I've got my "wrench" in place, holding my heater valve shut. I'm not happy with that and would like to put a ball valve on the heater return hose over at the PS of the firewall. Similar to Schocki's setup.
Does anyone know the ID of that return heater hose? It looks like about 3/4" but I'm not sure. Would like to have valve on hand before I cut hose.
Thanks very much for putting up with my ramblings,
Dave

 

Dave - trust me before you ever startup the heater core will already be fully at engine coolant temp - only takes a few minutes and it will stay slowly circulating by convection to keep it that way as long as the engine is warm. Due to that (and bulkhead area engine heat) the evaporator will be nice and toasty pretty quickly too - this is a shutdown issue not a startup issue.

I do not have the problem you describe, it may be that a little hot coolant can get through but certainly not much in my case - it is hugely better. Something must be different on the vacuum side for you. As to the valve - the flappy solenoid valve is the obvious choice here - its rated for the engine bay and it is stock vacuum equipment (even if repurposed).

Alan

 

Well I've gone full redneck. I have my "wrench" torquing the heater valve arm closed, and I put a pinch type hose clamp on the heater return line.
I'm not sure any of this is worth the trouble. If I park for 8 hours, the car and heater core and HVAC system all come to maybe 120-140 degrees in the hot summer sun: then the a/c will blow hot air for 5 minutes or so.. Doesn't matter if the heater valve is open or closed. First trip of the morning, everything is cool and the heater valve closes before the coolant gets hot. The only time it might make a difference is hot restarts within an hour or so; then it will blow hot air for 5 minutes or so, if the heater valve was open.
I think I'll just let it go for a while and maybe think of something better.
Thanks,
Dave
PS I took the pinch clamp off the heater return hose, because I am afraid it might cut the hose.