i have a 2001 highlander when I cut the ac or heat on makes a high pitch sound on 2001 Toyota Highlander

only does it when I cut the heat or ac on,just makes a high pitch sound,could it be the fan

Asked by for the 2001 Toyota Highlander
it may be as simple as a belt. the AC compressor engages when the AC is on and throughout certain times when the heat or defrost is on in order to keep the compressor lubricated. it would be a good idea to have the belt and AC compressor checked.