Very common scenario these days for 2 speed fans !!
The resistor may be u/s.
If it's been u/s for a few months and the AC has been used,
The fan will have only been operating on HIGH speed cycling on and off every few seconds. (this puts excessive current through the high speed relay. They are rated at 40 amps and the 65 amp surge with sudden high speed demand welds the contacts together eventually)
AC should not be used if SLOW speed isn't working as the resistor acts as a "soft start" circuit for the HIGH speed.
If the resistor is OK and high speed relay in the control box is OK you are looking at a duff motor or corrosion in the factory wire joints between the fan plugs/ control box and motor itself or the 80amp fuse.
The fuse very rarely fails but when it does it will be for a reason.
Happy fault finding and if you need a new motor kit look no further
Revotec cooling kit
http://www.the75andztclub.co.uk/foru...d.php?t=189409
Jules whole forum shop index
http://www.the75andztclub.co.uk/foru...splay.php?f=74
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This is what the R40 75ZT should have had fitted from day 1
Quality part manufactured by Revotec
Advantages over the OEM motor and other after market equipment:
Waterproof motor
Front mounted motor (away from hot running condenser)
Less current draw for same air movement
Long life motor (designed to run 24hrs for refrigerated cabins etc)
Front stone guard (safety feature plus extra protection for the condenser
Lower cost than OEM but better quality
Easy to fit (installs straight into Siemens/Rover cowling)
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