Heater controls (yet again)

[dnb]

While on holiday I had time to fix my problems with the heater controls. They now work - at least everything that should move does move and the white spots line up with the marks in the off positions etc... (incidentally, TVR put the mark in the wrong place on the water valve, so this caused much initial confusion)

I was going to make up a microcontroller based heater ECU to replace the thing TVR made, but now the problem isn't as straight forward - the problems are more fundimental than simply bad control.

So, all the components seem to work as it should. This should mean the heater works properly. Alas, this is not the case. The water valve opens and closes completely in one turn of the control knob - half way is fully on... Not ideal, but that's just TVR eccentricity. The valve is air tight, and this does stop hot water getting in the heater matrix for a while. But after a couple of hours on the M-way, convection has done its business and the matrix is full of tepid water and the heater blows warmed up air. No problem - there are windows to open - except that M-Ways are noisy places where windows are best left closed if you want to talk to the other occupant of the car.

Now I think I see why the cars with AC might struggle if they have the same heater matrix design... I'm wondering if 2 motorised valves is the answer? One each side of the matrix.

The rest of the controls make the right noises and seem to do the right things, but I can't help thinking that there's a better way of doing the heating. (and maybe getting limited AC)

Off to do some experiments...

[mongoose]

Are you sure it's a convection problem Dave?I only ask because the valve motor can move after a little while,all of it's own accord,sometimes you can hear it moving on its own!I guess this is down to the reistance value of the pot changing,due to heat soak.I'm going to fit an isolator switch to my motor power supply to overcome this.
I feel it cant be convection on mine,as if i put the cold position in the middle of the control knob travel,i can always find cold again after it has moved,just by the slightest tweek of the knob again.My valve must always be capable of staying firmly sealed to achieve this.If you need a new valve,then there was a thread on this recently with details on where to get new ones for £12 or so from memory.

[dnb]

Pretty sure it's convection but I'm not ruling anything out. The valve doesn't pass cold air (when being tested), but maybe it does pass water when it gets warm...

I had the valve positioned to closed and disconnected from the controller, so I don't think it's moving just to be awkward.

[david beer]

I have isolated my valve motor so it can not "creep" open, i have a spare push switch on the control so, unless its pressed in, the motor will not creep. There is also the case of the inner wing getting hot, even at speed it will get hot, extra heat shield will help with this and keep the fan on all of the time to move the air out of the inner wing, every litle helps !!