95 Nissan pathfinder

My pathfinder is getting hot when the a/c is turned
on. Even the heater. But it idles fine..back at normal
temp. Ive driven it around quite a bit. Sometimes it
gets hot..sometimes it runs just fine. Sometimes it
just runs a little warm and sometimes it runs
maxed out hot. But the vehicles running great. Its
like its the heat sensor...so ive bought a thermostat
and a heat sensor. About to put them on. And
change the air filter and check for rats nest. I also
had a mechanic check out the mass air flow
sensor..he said its working fine. My main question
is could it be something else? Im thinking water
pump and timing belt are fine. Even thinking its not
the thermostat. Cause its not always overheating.