my radiator fan wont turn on,unless i turn on the a/c

What is your question?

recently had work on it, intake manifold was repaired, the following night car starts to overheat radiator goes out had it replaced along heater hoses the the water pump but what ive noticed is that the temp. gauge goes passed the half mark to the point that its in red. i dont hear my fans go off... but when i turn on the ac the work to keep the engine cool, but i dont it starts to heat. i dont know what else can it be.