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I am try to understand if this valve can fail in a condition that would cause it to not close all the way. Anyone have any quality issues with this valve? It seems to be working properly with Vacuum and holds vacuum just fine. I can see the armature moving to the fully closed position.
For those interested. I am chasing an issue where I always have some amount of warm air entering the cabin. The warm air is warmer than the ambient air temp. I am narrowing my troubleshooting to the heater valve since I have verified:
- no vacuum leaks
- vacuum actuator is functioning properly under the correct conditions
- temp slider is on max cold
- flap setting motor is in the coldest position
- setting flaps are properly adjusted and in the fully closed position.
Is the warm air coming in from the vents? Or could it possibly be that the warm air is coming in from the shifter area? When the MMs are collapsed, it lets the torque tube drop down a bit which allows hot air from the engine to creep past the foam that normally seals that area. Same thing can happen with collapsed transmission mounts.
Is the warm air coming in from the vents? Or could it possibly be that the warm air is coming in from the shifter area? When the MMs are collapsed, it lets the torque tube drop down a bit which allows hot air from the engine to creep past the foam that normally seals that area. Same thing can happen with collapsed transmission mounts.
The warm air is from the vents. I replaced the motor mounts this past winter so those are still good. Do you have any experience with this heater valve?
To answer your question, yes they can fail, but it's unlikely. Easy enough to test, buy a cheap hose clamp and pinch off the hose before or after the valve & test again.
I recently fixed two "heat always on" cars, my 87 and a friend 86.5.
The issue with these cars is one or more vacuum actuators in the system was leaking, causing the whole system to lose vacuum at some point. If anything in the system is failed, it will allow the comb filter, or blend door or something to remain in the wrong position allowing warm air in.
Even if that valve is working 100% correctly, the heater core is still going to be significantly warmer than ambient. The blend door needs to be shut and also the comb filter comes into play. Also the fresh air re-circ flap plays a part since those stick open and can leak in warmer air.
Long story short, time to pull the vacuum solenoids and test each vacuum circuit. If any one is leaking, there's your problem and some of your solenoids could be bad as well.
Here is the best how-to on the job: http://dwaynesgarage.norcal928.org/1...0Procedure.htm
The 86.5 still has "phantom" warmth coming from somewhere. I suspect what John said above, it's coming from the TT tunnel.
Thanks for the tips. I gave the cable the pinch test and didn’t see any change in temps so the heat must be getting in another way
Remember, only one hose to the heater core is blocked by that valve. The other hose has a clear path & as the coolant heats up, so does this fluid and the heater-core itself. Even with a fully functioning valve, the heater core is still going to be significantly hotter than ambient temperature. I've often pondered adding a second valve.
There are multiple ways for airflow to find their way through the core and into the cabin. In order for this system to work properly, every path for the vacuum must be leak free. There are 5 solenoids (these can leak) and four vacuum actuators (with diaphragms that will fail), along with multiple runs of vacuum lines.
Any one of these could be leaking and cause you to have heat when you don't want it.
This is also assuming the HVAC head unit is problem free.
Repairing everything is covered in the link I posted above.
Good luck, I recently completed the "pod and center console" R&R on two cars. It's not that bad. The worse part is finding just how many plastic tabs all over are broken. Like the ones that hold down the console.
It's a good time to replace the ODO gear, ignition switch, and add some LED's to the POD while cleaning up all the electrical connections.
i am pretty sure mine is starting to fail as i can hear a slight trickle of water in the cabin which stops when the hose is clamped.
or does it matter which way around it is?
does the metal hose end of the valve go into the engine side hose or the cabin hose?
I'm out of stock on them right now, but I am told they should be here tomorrow. I think I remember seeing an arrow that designated coolant direction of flow on them, but I want to look...
It's a bit pricey, but that's not unexpected when the part is all metal. I wonder if the hose bibs are the right size.
Looking at the size of the vacuum diaphragm on that model, I also wonder if it will fit into the space envelope we have on a 32v 928.
Not sure how Carl's product works, but the stock valve has a spring loaded door, which allows a small amount of pressure to flow in the reverse direction.
The result is a certain amount of backflow...which ensures the heater core is always warm, so there will be instant heat, if needed. (German cars, colder climate.)
There's a door inside the HVAC that completely isolates the A/C evaporator and the heater core. Most all of these doors have long lost their foam and leak...allowing heat in. (The door can be adjusted at the main HVAC "computer", BTW.Sometimes this helps.
Very common for us to add a second heater control valve to shut off the "back flow", so the heater doesn't get any hot water, when running.
Of course, if one of the interior vacuum pods is leaking (super common), this must be repaired first , so that the heater control valve/valves can get enough vacuum to close.
Always start with testing the vacuum source and check valve. Move inside to testing the vacuum pods, heater control vakve, and vacuum switches. Then make sure the door between the heater and the A/C closes mechanically. If you still get heat, the foam on the door isn't sealing and you can then add a second heater control valve.
Beware: There are many different heater control valves, out there. I had a car come in, last week, that had a valve which closed with no vacuum and opened with vacuum....completely opposite of what is needed.
Great, now I'm stuck thinking about the old idea of two valves to prevent any hot water from warming up the core.....
early 944 had a manual (bowden cable) heater valve, believe it totally shuts flow off.
OT to anybody with this special valve being discussed but would you be able to take a photo "down the barrel" to show what the actual mechanism inside looks like? Butterfly or otherwise?
06-25-2018, 02:23 PM
928 Motorsports Heater Valve
