engine getting high temp during uphill

[macho palito]

Hi there...I've a problem with my car...it's a 1994 nissan altima...mataas kasi un menor when i start the engine then medyo nababawasan when i turn on the a/c...the first mechanic that i consulted told me i had to change the cylinder head kasi daw may singaw na un makina...but when i consulted the mechanic from shell...sabi nya pwede pa daw un cylinder head...ano ba talaga?

try to have your idle up controller checked...based on the observation that when you turn on the AC, the rpm goes down.