I have a 1998 Mercury Mountaineer that has an A/C fan unit that is intermittent , I have changed the resister and wiring tail, the fan speed control switch, and the mode switch. the compressor will engage but the fan and actual a/c in the interior is very intermittent and unreliable, in fact it is off more than it is own. I also changed the fuse switch. What else could it be.
If you mean fan blower inside car has an issue perhaps the resistor block for the blower fan has a problem or the interior blower fan such as worn brushes. If it's the fan in the engine I would look at the relay. You could run a jumper wire at the fuse box to see if that comes on or not. The inside of the relays get carbon build up and get wonky.
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