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Fan blower Speed Control Resistors - Metro based. 
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Joined: Sun Oct 19, 2014 10:10 pm
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Location: Bristol
GTM: Spyder
Post 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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New resistors.jpg
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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
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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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Testing.jpg
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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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Mounted.jpg
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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
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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.


Tue Apr 07, 2020 9:07 pm
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Post Re: Fan blower Speed Control Resistors - Metro based.
sanzomat wrote:
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.


I have to say that was my first thought

On the buggy I had a similar arrangement but with ceramic resistors, I know from personal experience they do get hot, you can imagine how I know, I mounted mine on a piece of aluminium chequer plate that was lying around. I have also wired some similar looking ones into my son's recovery truck for his LED tail lights & again they do get warm.


Wed Apr 08, 2020 1:14 pm
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Location: Sheffield
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Post Re: Fan blower Speed Control Resistors - Metro based.
Had similar.

http://www.sidewinderforge.co.uk/netlib ... tmlb7.html

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Thu Apr 09, 2020 11:42 am
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Joined: Sun Oct 19, 2014 10:10 pm
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Location: Bristol
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Post Re: Fan blower Speed Control Resistors - Metro based.
I've now spaced the resistors of the base with some 1/2" ali channel I remembered I had in the shed to allow air all round them. I ran the fan on a low speed for an hour beforehand though and whilst the resistors get warm they don't get too hot to touch with bare fingers so well under the melting point of the plastic. This modification should take away any risk.
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Raised up.jpg
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Covered over as a splash guard and to protect from the spare wheel
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covered.jpg
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Your solution looks a bit high tech for me Sidewinder - I like simple (like my mind!)


Thu Apr 09, 2020 4:31 pm
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