Fan blower Speed Control Resistors - Metro based.
Not sure if this has been covered before but I couldn't find a "how to" so here is one. Should be similar for any Rover Metro based heater blower so Libra/Spyder and probably K3 too? I had noticed that the heater blower was only working on maximum speed. When switched to the two slower speeds there was no fan motion at all. I know this is a common issue for many modern cars as the slower speeds are controlled with inline resistors and as they take the full current and the manufacturers like to penny pinch, the resistors are always close to the limit on current rating. To be fair to MG-Rover the fan resistor on mine had come from the donor Metro and as these are riveted to the heater unit it is almost certainly the original so has been in service since 1994. Blower resistors on Mk5 golfs last about 18 months max. These resistors aren't a service part on the Metro heater so the only option is to replace them with suitable power resistors. A quick search of the web informed me of the right ones - only 0.5 ohms but need to be 20a rated. I ordered these from ebay about 6 weeks ago and they arrived from China today. Hopefully 6 weeks in the post is enough for any Corona to have died off. Shiny!
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This is the old one, although under a metal shroud it is open to the weather under the front clam so a bit of corrosion that could be a clue to why it isn't working
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Old resistor.jpg [ 300.59 KiB | Viewed 6283 times ]
I did a few tests with wires with croc clips to confirm the optimum arrangement and went with 2 in series for the step from slow to medium speed and all three in series for slow speed. For full speed the resistors aren't in the circuit.
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I mounted all three to a bit of upvc I had in the shed and soldered the connections with some thick wire and adhesive fixed the slab to the bulkhead plate. I later made a cover from some plastic packaging to try to divert water away but didn't photograph that.
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Here is the old resistor removed from the car. I can't see the break but it is definitely open circuit. I now have nice fully controllable 3 speed blower again!
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Old resistor off.jpg [ 268.22 KiB | Viewed 6283 times ]
Edit: It has been pointed out that these resistors get a bit hot in use and might melt the upvc I used to mount them so I'll be keeping an eye on this and maybe changing the mounting plate! When I tested them they didn't get more than "warm" though so we'll see.