I've just bought a 1992 Roadster and have a couple of questions about the heater controls as I don't think mine are working correctly. The heater fan only operates on position 4 (maximum), and not on any other setting. The air conditioning seems to work (revs alter), but the blue AC light only lights up when the fan switch is in postions 1, 2 or 3, when the fan itself doesn't. On position 4, when the fan does work, the AC light goes out - I doubt this is as it is meant to be! (3/00)

The fan problem is almost certainly due to failure of one or more components of the resistor pack which controls the heater fan speed. You'll need to remove the heater fan (behind LH end of dashboard). The resistor pack sits inside, in the air flow, just near the exit. A replacement pack is horrendously expensive (50 - 60?) - ask your Mazda dealer and don't accept any "It'll have to be ordered from Japan" rubbish". There is no difference between non-aircon and aircon cars in the resistor pack.

When this happened on my 626, I replaced the pack with some resistors, but you can't just use tuppenceha'ppeny ones - you need power resistors - 50 Watt minimum. You can get them from RS, but you need a bit of fancy electronic mathematics to work out suitable values - you need resistors of less than 1 ohm.

Alternatives: For second hand spares, try Jay Ng at Powerdrift, or Ka Yu autos, or a new name has appeared - U-Save Automotive, or it's quite likely that some lesser car's resistor pack will do the job, but I wouldn't really know what to suggest. Mondeo?

I can't quite see how that can affect the aircon warning light, but it wouldn't surprise me if it's all the same fault. (3/00)
Thanks for the info. The same thing happened on an old Renault Gordini I had. I'll have a look soon - presumably I can just remove the glove box to gain access, or do I need to take more? (3/00)
Yep - in fact if you remove the glovebox you will find that the resistor pack actually screws on the outside of the blower casing (sort of underneath), and pokes inside. (3/00)
Thanks to help so far offered, I have located the problem with the heater fan on my Roadster, which would only operate on full speed. On the resistor pack, the four main 'legs' were fine but the one that bridges diagonally was broken. Someone had previously had a go at soldering this back together. As one part of this is much thinner than the other, I was wondering if it was some kind of safety overload/overheating device? When I bridged the two parts with a fuse, the fan worked on all speeds. With a bit of judicious bending, I have got the two parts to meet without actually fixing them together as this looked as though it was how they are meant to be. Does anyone know how they should be? Would it be OK to permanently link them or not? (3/00)

Well, the circuit diagram shows a fuse of some type in there. It is highly probable that it is a thermal fuse - ie blows if it gets too hot rather than on the basis of carrying too much current.

Just looked in my handy RS catalogue on CD - you can get TCO's (Thermal Cut Outs) which will carry up to 16.7 amps and go up to 215 deg C. They cost about 50p each - min order 5.

These things aren't easy to fit - you can't solder them for obvious reasons. You sort of twist the wires together. Probably worth a try with something like a 120 deg C version - you might need to go higher, but not much..

I wouldn't leave the circuit unprotected. (3/00)

Solder them quickly while using a pair of pliers need the body as a heatsink. If you tin the device lead, tin the wire and then solder it you can keep the overall heat you dump in well down.

BTW You can also get similar things that auto-reset. The electric window lifts use them - when the motor stops the stall current causes the cutout to trip and this cuts the juice. I don't know what they're called or where to get them as I recycled my old ones when making my new box. I guess alarm companies can get them as I'm told they can die. (3/00)
I got a non resetting one from Maplin for the princely sum of 54p. I decided to fit it by soldering wires to the split link on the resistor pack and using a small chocolate block connector. With a bit of juggling, this manages to tuck between the main block and the base of the unit and so goes back through the hole in the heater casing! This means I can easily change the thermal fuse if it goes again. I have put in a 128 degree as it was the closest that Maplin had to the suggested 120. (3/00)
Just got the car back [from having aircon fitted - Ed] Everything looks fine but I still have a question. Aircon is on as long as the fan is on. If I turn the fan off (zero) green light on the air-con switch goes off and I can hear the revs drop. Is this how it is supposed to work? I actually like it this way I can it on and just turn fan switch everytime. (8/00)
Not sure, on a MK1 the blower knob has a button in the middle so that you can have the air con on or off. The knob has to be on 1 or above though or it does not work. From what I understand it sounds like you have to have your air con switched on all the time (while the fan's on). This is not necessarily good as it means you are stuck with air con on all the time (less power, poor fuel economy). (8/00)
That's exactly how it's supposed to work. Green? Mine's blue. (8/00)
Yes, That's how it works - no point in running the compressor if the fans off. Beware of watery leaks in the passenger footwell - I had mine fitted from new and they didn't connect the drain pipe properly. First time I used it I had a footwell full of water. Dried out quickly enough and fixed it myself. (8/00)