If I turn the A/C on, the fans will turn, run for a bit, on and then turn off. At that point the A/C compressor begins to cycle. I assume from high line pressure. What is the normal operation? Should they turn on when the A/C is on and STAY on?

 

I'm assuming you have 2 fans on your car.

Driver side should turn on and stay on with the A/C. The passenger side will turn on when the high side pressure gets to 233 psi. On my car, the passenger is sometimes on, sometimes off. It's also controlled by the temperature sensor in your passenger head. (Mine has been changed out to a 200/185 on/off sensor)

Now if you have a pre 1988 car, I believe the passenger side isn't controlled by the A/C and is only controlled by engine temperature. In that case, it would be cycling on and off whenever the coolant temp sensor in your passenger head has reached it's turn on temp.

 

My car is an 87 350 formula with dual fans.

 

The primary runs when I first turn the A/C on, and then turns off. At that point, the A/C compressor begins to cycle.

 

My car is doing the same thing. It is a 89. I am tempted to wire the fans to stay on the whole time it is in ac mode. Theres no way it can be cooling effeciently withe fans turning off with the ac compressor engaged

 

The extra fan is only neccessary at low speeds and stays off when at hiway speed. That is the reason for the pressure switch.

 

Im talking about the primary fan. Even when I bypass the pressure switch, the fan is still not running.