It seems to be a common problem with the heating system in the Griffith that it is impossible to turn off the heating completely, the warm or hot air that is continually blown into the cabin can make summer outings rather unbearable, this is certainly my experience. Heat regulation is achieved via a water valve in one of the heater matrix water pipes. The system uses an electric motor to move the valve, controlled by the top left hand heat knob on the heater panel. The position of the valve is tracked by a servo system that uses potentiometers (variable resistances) one attached to the motor spindle, the other to the heat control knob. When the heater knob is rotated a potential difference is applied to the motor and it drives the valve until the rotational position of the two potentiometers is the same, i.e. if the heat knob is rotated say from 12 o-clock to ten-past the motor will drive the valve until its potentiometer also reaches ten-past, at this point the potential difference is zero so the motor then stops. In the simplified illustration below both potentiometers are midway so that 6 volts is applied to both sides of the motor, the potential difference is thus zero and the motor is at rest with the valve half open.
Diagram to illustrate the operation of the water valve servo (simplified)
To Align The Water Valve Servo
A few pictures will hopefully explain the operation of the system. It is essential that when the heat control knob is at a minimum the valve is fully closed, this is frequently not the case. It is much easier to remove the valve to investigate.
The water valve
The basic water valve with the motor detached is shown above, note the white paint marks on the movable arm and the valve body. When the arm is in this position the valve should be fully closed, this may be checked by blowing into the valve. The Servo motor with its reduction gearbox is seen below,the drive pulley is secured on the shaft with a Philips headed bolt and then fixed to the valve arm by two small bolts (seen on the water valve arm above).
The servo motor and gearbox
A rear view of the complete assembly is shown below with the extended motor shaft that drives the motor potentiometer
The complete valve unit
The valve unit is fitted to the heater matrix rubber tube in the passengerfoot-well. The motor servopotentiometer can be seen hanging freely with its blue/green/white connecting wires.
The water valve fitted in the heater matrix water pipe
1. Set the heater temperature control (top left knob) to minimum
2. Ensure the water valve is set to off, i.e. with the valve arm and valve body white marks coincident
3. Loosen the Philips-headed bolt securing the pulley to the shaft
4. Allow the motor potentiometer to hang free as in the illustration
5. Turn on the ignition and the motor should start running
6. Adjust the potentiometer with a small screw driver until the motor stops. Hopefully the white marks will still be coincident, so secure the pulley on the shaft and fit the potentiometer on the shaft end (just a push fit) making sure that the slot engages correctly on the shaft flat
7. Rotate the heater control knob throughout its travel and note that at maximum with the water valve fully open the valve arm has only rotated through about ¼ of a turn
8. Rotate the control back to minimum to check that the valve closes again with the white marks in line
The above sequence may have to be repeated a few times for accurate tracking.
Even with the water valve correctly aligned you may still find that the heater pumps out a fair amount of heat when at minimum. Some owners report cool air but most complain of uncontrolled warm air.
Note: The above explanation is simplified as in practice the heater control unit HCU (electronic black box) is used to amplify the small current variations from the potentiometers to a level sufficient to drive the 12 volt motor. If the above does not fix your problem you could have a faulty HCU. Replacement is probably then the only solution.
I found that even after careful alignment instead of permanent hot air, warm air was still circulated with the valve closed. It seems that despite the valve being closed heat still gets through to the matrix. As a test I made up a temporary blanking plug and inserted it into the heater supply tube from the inlet manifold under the ignition coil, the result was cool air even during a long trip.
Heater Blanking Plug
Some early cars have a heater bypass arrangement so that water still circulates from the inlet manifold feed even if the electric valve has stopped the flow to the heater matrix. Steve Heath shows this in his Griffith/Chimera manual.
Later cars do not have the bypass so with the electric heater valve off no water can circulate from the inlet manifold feed so fitting a manual in-line tap to these cars should not cause any problems.
As a permanent solution a suitable heater tap was found at Europathe 16mm version fitted my (1996 Griffith 500) heater tubes. The ignition coil was unbolted to allow access and a section of tube was cut out to allow the tap to be inserted, the tap fits conveniently and neatly under the coil.
In line tap shown in the heater supply from the inlet manifold
It is now a simple matter to effectively shut off the water supply in the summer, and at last some cool air!
Note:Some Griffith’s owners have expressed concern over this modification so do take expert advice before proceeding.