2004 Mercury Monterey A/C

We had to change the radiator and now after recharging the A/C the cooling fan doesn't come on to cool the A/C and the pressure goes through the roof. Fan works fine to cool the motor. Main fan comes on to cool motor, is the small fan just an aux. fan or is that for the a/c? Everything was working fine untill we changed the radiator. We've made sure everything is plugged in.