my head pressure on low and high is going out of sight, what activates the fan relay when pressure gets to high?? my fan is coming on when temp get up so relay is good ,just not coming on when head pressure up with a/c on

 

If you have the two fan system GM made the Passenger side fan come on at 220 Deg with the A/C on, otherwise it does not run. I feel 220 is too hot for me trafic and it is only 180 deg on highway. But that is my opinion and not too much you can do, except install a manual fan switch which I don't like. Anytime you start hacking it only screws things up more.

 

there is only 1 fan ,, my head pressure is over 300 on high side and i turn the a/c off because stuff starts making noises, it should activate something to turn on cooling fan to lower a/c head pressure""" somebody correct me if im wrong,