fan on constantaly and temp gauge no working

[sb2010]

my fan is on low speed as soon as i start my pug 206 1,4 a/c,and temp gauge reading cold wen engine is hot,and bottom rad pipe is cold all rest are red hot,put new temp sender in new fan sensor rrhh heaters go hot n cold as well need help plz.is this due 2 broken water pump or air lock in coolant system