Removing the Heater
Disconnect the battery before removing the heater. The Smiths "fug stirrer" heater is situated just left of the transmission tunnel inside the passenger footwell. It is attached to the bulkhead above by three spacer bolts. The heater is connected by four wires. Two wires are attached to a wire wound resistor mounted on the motor plate. They should be green wires. One has a yellow trace, whilst the other has a slate trace. The green wire with yellow trace connects one end of the resistor to terminal 2 on the heater switch. The opposite end of the resistor is connected by a green wire with slate trace to a 4 way bullet snap connector, which it shares with the positive motor wire. A green wire with slate trace connects the 4 way bullet connector to terminal 1 on the switch. See Figure 1
Detach the two wires connected to the resistor. Remove the motor earth wire by unbolting it from the bulkhead and detach the other motor wire from the bullet connector.
Under the bonnet, three securing bolts and the heater matrix tubes pass through the bulkhead. Remove the water circulation hoses from the tubes. If you have not drained the heating system, insert bungs in the hoses and tie the ends up above the level of the engine. The heater matrix remains full of water, even when the cooling system is drained. Support the heater inside the car and remove the three securing nuts. Carefully lower the heater and drain it.
Stripping and Servicing the Heater
Four spring clips hold the motor plate, matrix and fan housing together. The clips can be removed by prising them off with a screwdriver. After removing the spring clips, the fan housing can be removed. Make a note which way up the fan is fitted, then slacken the grub screw securing it and pull it off the motor shaft. The motor and resistor can now be separated from the motor plate by releasing the three spacer mounting bolts. Take care not to damage the resistor, as they do not appear to be available anymore.
The Heater fan is driven by a 12V 24W single speed motor. Unlike the windscreen wiper motor, it is not equipped with a second brush to achieve alternate speeds. When the heater switch is set to 'fast speed', the green wire with slate trace bypasses the resistor and draws current directly from the ignition auxiliary fuse.. When 'slow speed' is selected, the green wire with yellow trace is connected in series with the resistor and the motor draws a reduced current.
Figure 1 depicts live and earth motor leads, both the same colour. This is because the original Smiths motor was field wound, so swapping the earth and live wires does not alter the direction of rotation. However, if the motor has been replaced by a Clayton heater motor, the earth and live wires appear to be different colours. These motors can be connected up to rotate in either direction.
The motor is usually trouble free. If a problem exists, it is usually due to worn brushes. To examine the brushes, remove the two long bolts which pass through the motor housing and remove the armature. Examine the commutator for wear. The copper segments must smooth and stand proud of the insulation in the grooves between. If the brushes are worn it may be difficult to source new ones. It is always worth checking auto electrical experts in your area for advice. If you are lucky enough to own a lathe, it would be worth polishing and cleaning the commutator. Second hand motors are regularly advertised on ebay. If you are fitting a new or second hand motor, note which way the fan rotates. It should rotate in the direction indicated in Figure 2 and expel air from the vents. If it does not, and the motor is a Clayton one, swop the earth and positive wires. If an original Smiths motor is fitted, check that the fan is the right way up on the motor shaft. Auto Electrical Spares or Holden Vintage and Classic should be able to supply a Clayton heater motor which will fit the old Smiths heater. Before purchasing, check that the motor shaft is long enough to pass through the matrix, with enough room to attach the fan. An excessively noisy fan can be due to worn or dry bearings. Check the motor shaft for free play. If the shaft is free from play, a squirt of WD40 on the lower bearing above the fan should quieten things down.
The original matrix (heat exchanger) is the most vulnerable component of the Smiths heater. Being made of tinned steel, it usually develops leaks in old age. I remember soldering mine during the rebuild, but it only lasted a couple of years before leaking again. I replaced it with an old second hand unit which has remained leak free for the past 20 years. However, Clayton manufacture heat exchangers using copper wire wound tube. They produce a range in various sizes which fit Smiths round heaters and are available from Holden, who usually keep a range in stock, but remember to order one with the motor plate and always phone to give information regarding the dimensions of your own heater matrix.