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Montego Heater, Fan & Rheostat Tips

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  • Montego Heater, Fan & Rheostat Tips

    I was dissatisfied with the advice given in a thread now in the Electrical Forum concerning rectifying Montego air conditioning, rheostat and heater problems, so am posting these tips on how to solve problems at minimal cost. Clearly it is the case that these heater problems can cost a small fortune to repair, if a garage is used. I fixed all the problems at almost no cost, except in time and labour expended.

    I had two problems on my 1991 GSi Montego 2.0 EFi: there was a leak coming from the general direction of the heater, and the blower fan was very tempremental on all three settings. Having no experience of removing the dash, I managed to remove it quite easily with the help of an official Rover Manual for my car - the Haynes manuals I found to be out of date in respect of later 2.0EFi models; and they are not recommended. Especially confusing is the advice about the heater control unit switch panel, which on the later models, should remain attached to the heater housing by its two red and green wires. I removed the whole heater unit after removing the fascia.

    The leak was immediately traced to rusted Heater Matrix Pipes. The heater radiator itself was in fairly good condition, except that the foam surround had perished. I discovered the matrix pipes are now no longer available to buy, although there is a guy on ebay who sells internal radiators who says he can make them from brass for 45. However I managed to make some new pipes myself with the aid of 15mm chrome plated copper tube and a pipe bender. I then hammered off the three-screw connecting plate and the flange plate, and the intermediate securing bracket from the old rusted pipes. I then soldered (using normal plumber's solder) the new copper pipes I had made into three-screw connecting plate, leaving approx 3mm protrusion of the pipe at the other side of the connecting plate. After cleaning out the radiator I then placed the rubber washers of the radiator onto the 3mm protruding ends and bolted together with the radiator, making sure the seal was air tight. I then placed the heater radiator and bolted on matrix pipes back into the heater unit, and made sure the pipes aligned with the heater - may need to resolder if not properly aligned. I then secured the pipes to the heater using the securing bracket I had ealier hammered off the old pipes. In order to secure the flange bracket to the pipes, I used a plastic washing machine double-hose connector, cut in half, one half for each pipe, which slides neatly over the 15mm copper tube. It then makes a nice snug fit between the copper pipes and the flange bracket/plate.

    I found it unnecessary to replace the foam stuck to one face of the flange plate, which had perished. However I found many other foam bits had perished round the air conditioning parts, which I replaced with new bits of foam cut out from from foam carpet underlay of about 1cm thickness, which I was given free of charge.

    Now the heater itself cannot be pulled completely apart without damaging the plastic heater casing, because at the bottom of the heater one of the fixed metal plates is secured to both sides of the heater using non removeable fasteners. If you need to replace the whole fan unit, make sure that you damage the fan side plastic only, because then it is replaced by the plastic housing of the new fan. It's best to damage the plastic casing as little as possible because it is frequently the case, that there is actually nothing wrong with the fan itself, but it is the rheostat that is the problem; and the fan can be reused. When reassembling, just use normal screws of the appropriate diameter in place of the non-removeable fasteners.

    In order to access and test the rheostat (otterstat) you don't need to take the whole heater unit apart. Just remove all the clips at the top and sides and pull the heater apart at the top, and slide the rheostat out very carefully, making sure you don't damage the coils underneath. You need to use tools to keep the heater unit sides apart at the top, as they press closely together when still attached at the bottom. However this will save you a lot of time messing around with the non-removeable fasteners at the bottom of the heater housing.

    After electrical testing of the rheostat, the problem with the blower fan not working was discovered to be slightly corrosion between the two brass terminals at the centre of the rheostat. The way it works is that when there is overheating, either of the coils, or of the brass tongue in the centre of the rheostat, then the brass "tongue" in the centre of the rheostat bends slightly, breaking the electrical contact with the brass surround, causing the fan to become disconnected. What was happening was that the mild corrosion between the rheostat tongue and the brass surround was leading to a permanent / intermittent breaking of this contact, causing the fan not to work. I easily fixed the corrosion problem with a tiny piece of sandpaper, and a small screw driver, with which I sanded the corrosion off the rheostat contact terminals in the centre of the rheostat. I then re-tested and found the blower to work perfectly as before. Making sure that there was no point of inadvertent contact between the two coils, I re-inserted the rheostat into the housing.

    A new rheostat and wiring harness costs 115 BTW. A lot of money to pay when all that needs to be done is a little sanding of the rheostat terminals.
    LPG Converted Montego 2.0gsi 1991 - are there any others?

  • #2
    Further matters: I found it expedient to replace the rubber washers of the internal radiator with new 'O' rings to get a more air tight joint between the radiator matrix and the matrix pipes.

    The engine-end of the matrix pipes could usefully have a half a straight end-feed or yorkshire fitting soldered on to facilitate a water-tight connection to the radiator hoses.

    For testing, it is expedient to over-fill the radiator tank to generate a high water pressure when engine is left running to ensure everything air-tight. Naturally the dash should not be refitted until all testing has been completed; therefore a temporary connect of the ignition switch is required to turn engine on to test for leaks.
    LPG Converted Montego 2.0gsi 1991 - are there any others?

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    • #3
      The non-removable fasteners are pop rivets. These can be removed by drilling them out of the casing carefully. Upon reassembly of the casing, new pop rivets will be required. The heater fan itself could be removed for inspection and testing, by undoing the two screws in the fan side casing and withdrawing the heater locating plate.
      Replacement foam seals are required on the matrix to prevent cold air leaks from impairing the heater's performance.
      "Air Conditioning" is a bit of a misnomer here. Refrigeration as such was only available on Montego 2.0 litre models built to Middle East specification.
      M&MOC Committee Member - Archivist
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