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Thread: HVAC Controls

  1. #1

    Default HVAC Controls

    I've been on a weird adventure this past few months with my Noble, basically redoing a handful of stuff, trying to improve some other items, and making the car just easier to maintain for the long run.

    One of those items was the HVAC controls.

    Initially, I wanted to adapt a more readily available set of controls that would be easier to source in the USA, instead of the Ford Escort HVAC set of controls. Largely because the plastic knobs tend to break, the display panel will fall apart, etc.

    First, how does the Noble system work?

    1. HVAC Controls. This is the control panel in the center dash. This is the setup disassembled. Pretty straight forward. You have a 8 pin connector to the large switch that controls the fan speeds and AC switch, the rest is driven by cables. What is likely happening when you have a knob that doesn't want to turn is due to either the cable stuck, or the heater control valve stuck/frozen.
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    2. Heater Control Valve. This valve controls whether or not you get heat thru the vents. If you rotate the knob to hot, the valve opens up and allows coolant to go thru to the heater core in the dash. When closed, it just loops back to the engine bay. This is a basic Ford part. Thankfully it's metal, because it's less likely to break -- unfortunately it's metal as it can corrode. This part is bolted in the tunnel, directly under the center dash. To remove, you need to remove the dash, and some of the tunnel covers to access.
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    3. Inlet / Flap box. This sits under the front clam and is made of plastic. A UK user made a box out of aluminum that you fit your old hardware into. Worth looking into, but the flap controls are pretty basic.

    4. Fan / Heat Exchanger Box. This sits under the dash. I haven't bothered digging into all that.

    So, one of the issues with the Noble is tunnel heat. You have oil lines, coolant lines, heater core lines, ac lines -- all running down the tunnel carrying heat. One fix is to send some air down the tunnel from the front ducts to help with cooling that area down. This helps quite a bit, but can still be improved further.

    What I did was removed the heater valve from the tunnel to the engine bay. Why? Cause if I want cold, the hot coolant never enters the tunnel, thus never creates additional heat. Also, creates more space in the tunnel for other activities (not that important, but whatever).

    There are two ways of doing this:
    Easy method -- Move the metal heater valve to the engine bay. Buy two 5/8 hose barbs to fit into the hoses to re-use the hoses so they now connect to the heater valve in the engine bay. Buy a new control cable that can control the valve in it's new location.

    Hard method -- Buy an electronically controlled valve and install in engine bay. Buy two 5/8 hose barbs and extend hose runs to engine bay. Buy or build controller to control valve.

    Since I like challenges, I did the Hard method and opted to learn how to make arduino stuff instead of buying the $70 controller that would do it all for me:
    1. Remove old valve. My dash setup makes it very easy to remove the dash.
    2. Buy Thermotion electronic 4 port valve ($70):
    3. Install valve in engine bay. I mounted mine on a bracket off the center chassis brace.
    4. Buy Arduino Pro Mini ($10):
    5. Buy Arduino Mini H-bridge ($9):
    6. Buy Arduino starter kit ($37):
    7: Buy Arduino project box ($11) for everything to fit into:
    8: Buy Potentiometer ($6):
    9: Modify the potentiometer. The Pot I bought, when fully rotated left (or cold), it has a switch that turns something on/off -- then goes thru roughly 270' of sweep. I needed to remove the switched portion of the pot and then reduce the sweep. Removing the switched piece was easy, as I had to drill out two rivets and the black portion falls out. No more switch. The next part was cutting a new mechanical stop on the bottom of the pot housing so it rotates thru the same range as the OEM knob. A dremel adventure later, done.
    10: Program arduino to control the valve. This is the tricky part. Arduino can control a motor pretty easily. On or off. Cake. The problem exists with the valve is, to open the valve, you apply normal polarity... to close the valve, you invert the polarity. Arduino can't do this natively, which is why you use the H-bridge. Wire the H-bridge up to the Pro Mini, wire the two boards to the valve, and if you wired it smartly, you should have five wires left: two wires for power (12v ignition & ground) and three for the potentiometer (5v, signal, ground).

    Now that we have the potentiometer going thru the range that I needed, I captured that range data in the arduino, did some maths and converted that range to a percentage. The heater valve also has a pot built in that transmits the position the valve is in. Again, capture that range data in the arduino, do some maths and convert that range to a percentage. Now that we have the feedback set to a percentage AND the pot that "requests" the temperature, I can create a basic if/then scenario where the motor will run one way if the knob is set to cold and reverse polarity when set to hot. When the percentages are <= 3% of difference, shut the motor off.

    11: Install the potentiometer into the HVAC controls. A quick bracket, some minor cutting, and the potentiometer is affixed to the HVAC control panel. Hot glue the knob into place and now you got an electronically controlled heater valve, with a knob that won't freeze up or break off.

    Mind you, I went overboard with this -- but it was something I wanted to learn and see if I could make it work. The biggest downside of the electronic valve is it takes longer to get from cold to hot and vice-versa, since there's a motor opening/closing the valve, versus a cable that just makes it happen.

    The next step is to adapt a full HVAC panel from, say, a NC Miata. I wouldn't have to recreate the heater valve, since it's now electronically controlled and a new HVAC panel would just adjust the valve accordingly. I may just need to adjust the code a little.

    Anyways, long-winded thread -- mostly for me to reference later on when I forgot what it took to do.

  2. #2


    I was thinking of plumbing in a cutoff for the hot water hose in engine to stop the hot water coming down the tunnel.
    Are you seeing any impacts of in effect doing the same thing?

  3. #3


    Quote Originally Posted by AVFC80 View Post
    I was thinking of plumbing in a cutoff for the hot water hose in engine to stop the hot water coming down the tunnel.
    Are you seeing any impacts of in effect doing the same thing?
    If you're going to the effort of installing a cutoff, might as well just relocate the valve into the engine bay and buy a longer cable and two 5/8 hose barbs to join the hoses together. The cable is really simple, as it's a simple push/pull cable without any ends on it. Just a solid wire covered in a sleeve with a small hook bent into the wire at one end and the other end is bent to fit a plastic sleeve.

  4. Default

    Thanks for documenting sharing!

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