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To disconnect the cable from the screen/demist control knob, first gain access to the back of the control knob, either by removing the dash mounted radio/radio blanking plate on early models, or the fresh air vents, or the console assembly on later cars.
Photo 1 Spring off the control knob by locating the small hole and pressing in the spring retaining ball.
Photo 2 Undo the nut which holds the control assembly in place. Pull the assembly out from behind the dash to allow access to the cable connection.
Photo 3 Undo the inner and outer cable. Then disconnect the two hot air supply hoses which push into the bottom of the heater unit from deep inside the central tunnel.
Photo 4 Undo all the Phillips screws which secure the heater at its base and the single screw at the top. Now with the cable free you can withdraw the heater unit from the car. It will be necessary to lever and prise the unit from out of the recess in the bodyshell. After many years in position it will not come out easily.
Photo 5 Lever up the unit and pull it forward at the same time, in order to clear the rear lip along the top of the engine compartment. If there are any brake pipes located along the inside of this lip, take great care to avoid damaging them as you pull the unit away. It will require a considerable amount of force to free the unit, but once the old foam and rubber seals break away it should pull free. Gently withdraw the unit from the engine bay, pulling the attached control cable through the bulkhead behind the heater.
Photo 6 Spring off all retaining clips and lift up the lid from the unit. Now you can remove the old matrix and either refit a direct replacement or upgraded matrix. Note how the matrix goes in to the casing and the position of the packing foam. Take care not to refit the foam in such a way that it restricts the flow of air through the matrix.
Photo 7 The standard fan motor assembly fits through the hole in the lid and can be removed and replaced from outside the unit.
Photo 8 If you wish to fit the upgraded heater blower motor and blower assembly, now is time to do so, because the diameter of the uprated fan impeller is larger than the hole in the casing lid. Therefore, the fan motor has to be installed from outside the lid and then the impeller fitted on the inside of the lid. This can only be done with the unit removed from the car.
Photo 9 Included in the replacement matrix kit are a set of new foam seals and these must be glued in place with contact adhesive before reassembly.
Photo 10 When fitting the base foam, note the cut out area for the flap control and the position of the hole for the control cable.
Photo 11 Once the glue has dried, remember to make a new hole in the foam seal for the control cable to pass through.
Photo 12 Replace the heater unit lid and refit all clips.
Photo 13 Refit the control cable to the base of the heater unit, clamping the outer sleeve to the heater and fixing the inner cable to the flap control. Check that the cable fully opens and closes the flap, some adjustment may be necessary.
Photo 14 Replacing the heater unit. First work out the route of the cable back through the bulkhead and into the dash area. Thread the cable into the access hole, it is helpful to have an assistant working on the inside of the car to locate the cable and guide it up behind the dash. Avoid letting the cable curl up in some inaccessible area inside the bulkhead.
Reconnect the fresh air hoses and face level vents if fitted. Next and most importantly refit the two flexible hot air/demister hoses to the bottom of the heater unit. These two hoses feed into the base of the heater through the inner tunnel area beneath the dashboard. To gain access to this area, remove the trim panel and hose clamps. This will enable you to squeeze your hand inside the tunnel to push the demist hoses into position. Failure to reconnect these hoses correctly, will result in ineffective demisting.