Air conditioner fan only works on max speed holden service centre thought it would be fan speed resistor where is the resistor and how difficult is it to get to

sounds like the resistors that control the speed may be burned out they are usually located somewhere near the blower fan

It's common for interior blower speeds to only work on high when the blower resistor goes out. Usually located close to the blower motor. An electrical box/module with wires going to the fan motor. Goggle how to change it, and you'll know whether you can.

fans run even with blocked filters
probably find that the low speed fan resistor has burnt out or the vent control module is not operational

Unlikely a blower motor resistor problem. If the resistor is faulty. the fan speeds will not work/fail on the lower speeds. High speed will normally always work. If the fan is non operational suspect a fan motor issue.Bad fan motor/switch/wiring to it

Check the fan resistor. If you have power at the fan but no ground it's most likely the resistor

I would replace the blower motor resistor first then see if that corrects this. The resistor is located next to the blower motor under the dash.

when it's on 'auto', the fan adjusts according to the temp in the car and the temp setting you have it set at. try setting the auto temp control down to 65, then hit the "-" one more time to send it to "LO" - the fan should automatically jump up to max.

All cars are designed with a blower fan motor that pushes air through the ventilation system. This air is processed by a series of vents to direct the air to various positions. Example: heater, air conditioner and defrost modes. Most blower motors are power by a basic electrical circuit that utilizes a multi resistor or a solid-state resistor to control different fan speed modes (low, medium low, medium and high). If the resistor malfunctions it may lose one or more of the lower fan speed settings.
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if the fan/motor only works on max No 4 setting ? then may i suggest you have a resistor fault or commonly known as a reostat in uk this is the component that provides the relevent reduced speeds on selection but when it fails only max speed works so you should find this unit attached on heater fan exterior if you follow wires from actual motor it will connect to the resistor unit ? then onward to switch control it is not to difficult diy and if you have access to manual/ it will give location/access for renewing? hope this helps/inspires you to diy ?

When you find the fuse if it has blown also check the resistor to control the fan speed. I cant remember if the 1 series has a load resistor multi tap but it may have failed if you use 1 or 2 speed on the fan a lot, max will bypass the load resistor where as 1 will use maximum load and the thermal fuse might have blown. But replace it as caution. In the earlier models it had a block which was nicknamed the hedgehog, a load resistor buried under passenger foot-well up toward the centre, loads of spiky aluminum pegs which cold air blew over to cool it, always packing up in the earlier models £25 from scrap dealer cheap fix compared to the £££££££ BMW dealers rip off. Heater or air con would either not work or blow erratically. Hope this helps