Horton fan question

[birdshill123]

My ZHorton Fan is not operating properly. 1988 FC35. When I engage the
A/C the engine cools down. To me this means the sensor is not working.
The fan overide works OK. Where is this sensor located. Can it be
accessed without a rad removal? Is it a Horton part? Bb Part or Cat?
The Horton manual lists both N.O. and N.C. sensors. Which is the
correct one? Good source for the sensors?

Thanks

Bruce FC35 1988