I put heat on the ON position and the heat comes on with fan working. It runs good for 10 minutes and then the fan turns off but the heat is still working.
I put the heat on the AUTO position and turn the thermostat up to 90 the furnace works but he fan does not come on.
The cool on the ON position ,and the outside compressor and fan works but the fan doesn't work on the inside. A few times the fan did come on with the cool on but not too many times and the fan shut shut off after a few minutes but the outside continued to work.
The cool on Auto , outside ac works fine and the fan on the inside doesn't turn on.
What could be causing this?

Thanks very much