Mrmerlin

please fit the factory heater control valve,
it is the weak link in the sytem and you should keep it that way.
as the least amount of damage will be incurred if it should fail

dr bob

Our wx is upside-down from yours. We know it's winter only when it doesn't reach 70º by mid-afternoon. If we had measurable snow here, traffic would come to a crashing sliding halt. People would jump out of their cars in their flip-flops, tank tops and shorts, swear and shoot at each other, then jump back in the cars and try to figure out how to get the heater to work to thatw their little frozen toes.


Yes. It needs to be installed in series with the existing valve though. Vacuum for it would tee from the hose to the rear fuel pressure damper to get it to work.

The amount of space to install it is quite limited. The fuel cooler is in the way on the firewall, and the rest of the area is pretty full of airflow sensor and the fuel system plumbing. The valve could be installed anywhere in the loop between the existing heater valve and the heater core, but that's about a foot of formed hose there. I'm pretty sure it will fit there somewhere, just not sure exactly where. It would solve the problem though.

SQLGuy

Why in series? I would plan to switch the logic on the vacuum manifold solenoid to provide vacuum when 12V is not applied to the coil, and vent when 12V is applied. At that point, I would expect I could replace the stock NO valve with the Fiesta NC one.

dr bob

Trying to find the least invasive, most easily reversible solution I could so the car can be made original again most easily.

I've inadvertently inherited some cars that had hack solutions or fixes applied. It's really easier fixing the original to original function compared to chasing down original pieces that got tosses or modified until there's no functionality remaining. Adding the Fiesta valve sacrifices only a formed heater hose, something that's available and already on the periodic PM schedule anyway.

What's your thinking on modifying the solenoid logic? I thought about that some, but dismissed any option that requires current for a solenoid while the engine is off. So I started thinking about another solenoid in series in that vacuum circuit between existing SOV and the HCV. Coil to circuit 15 (on with key on/run). Inlet from existing solenoid to what's typically the output to the ctuator on the new solenoid. HCV would connect to what's normally the vacuum source port on the new solenoid. With key off, the HCV would be isolated from the vacuum system. I was thinking about adding a small accumulator in the line between the HCV and the new solenoid, maybe a few incheds of PVC with caps and one small vacuum connection. That would hold the HCV closed during the transition from key-on to engine running on hot restart. Look at the solenoid used for the flappy as an example of what to add. Again, painlessly reversible, gets power from something like the cigarette lighter circuit that's only on with key in position 3.

SQLGuy

Well, my thinking was, if I had a NC HCV, I'd need to be able to apply vacuum to it when the HVAC head wanted heat.

Currently the HVAC head gets heat by removing 12V from the red wire to MV5 (the vacuum solenoid in the manifold under the center console). This closes the solenoid, allowing the white line to vent and opening the stock valve.

With an NC valve, I would instead run the red wire to the base of a PNP transistor, with its emitter tied to ignition 12V and its collector connected to MV5 where the red wire used to go. A resistor (value dependant on transistor's hFE and MV5's coil resistance) would go from the transistor's base to ground. With this setup, the vacuum solenoid would be closed (venting the white line), when the ignition is off, or when 12V is applied to the red wire (reverse biasing the transistor). When 12V is removed from the red wire, but the ignition is on, the resistor will forward bias the transistor, pulling the collector up, energizing MV5, and sending vacuum to the HCV.

So, where currently we have

12V (on red wire) = vacuum = close NO HCV (no heat)
and
0V = no vacuum = open NO HCV (heat)

we would instead have

12V (on red wire) = no vacuum = close NC HCV (no heat)
and
0V = vacuum = open NC HCV (heat)

Everything works the same, except that the HCV is closed when the engine and ignition are off.

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However, the suggestion of the in-line vacuum solenoid to keep the HCV from venting also sounds good.

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By the way, though, since this heater core heat soak issue would have existed in every new 928, I still have to feel that the mixer flap foam being all rotted is part of what's making this an issue. Is it reasonably possible to replace this foam, or is it a major undertaking (ala changing the front evaporator)?

SQLGuy

OK, here's the plan:

1. I bought this valve, which looks to be the same as the 4 Seasons one I have in there now, but NC instead of NO. http://cgi.ebay.com/ebaymotors/VACUU...item3caeafc00f

2. Should have the replacement comb flap actuator parts in the next day or two.

3. I've had on hand a cabin temp sensor and a block of insulation foam for around the shifter that were both waiting on me getting around to pulling the center console.

I plan to tear into the car next week, pull the center console, swap in the sensor, bladder, foam block, and do shifter bushings and trans oil change at the same time. While I'm in there I'm going to see whether replacement of the mixer flap foam seems possible/practical. Then I may switch the heater valve to a normally-closed setup.... I'll update this with what I find.

Cheers,
Paul

Speedtoys

So whatdidja find?

Im curious if you have a photo of the insulation foam you added under the console.

blown 87

I just go in and replace all the vacuum pods and heater control valve, if the OAT sensor is working that will fix the majority of the problems folks have with the HVAC as far as to much heat.

Do it once, do it right and be done with it for a few years.

SQLGuy

This is the foam block. I still haven't replaced the orginal one, since I haven't yet done the front shifter cup, which would have been an excuse to drop a lot of the stuff I would have needed to do to get to this block.

I replaced the vacuum diaphragm, but the NC HCV, while the same style, is too small and I was not able to find a correctly sized one yet.

Greg, everything is working correctly, but the heat soak of the heater core when the car is parked for a while is still really annoying and makes for a lot of extra heat that the system has to get out of the car. The car will eventually cool down to the point of closed-loop climate control, but it would happen a lot faster if it weren't neccessary to pull all that extra heat out of the plenum.

I think it's kind of funny that a number of people on this forum on the one hand defend the design, while in the next post suggesting just to tie strap the valve closed in the Summer. If it's such a proper design, tie straps shouldn't be needed.

Speedtoys

Thanks for that..I thought that was under the car, not under the console.

SQLGuy

It's under the shifter linkage, so, yes, under the car. As I understand it, it presses up above heat shield above the torque tube.

Landseer

Similar for automatic and manual.
Its butted against car.

When MMs sink, air can enter the car at the shifter / console

blown 87

I am not in the tie the valve up camp.