A/C compressor maintenancae

[mohsen]

i went to A/C maintenance shop and he remove the compressor and replace 3 oil seal on it
and install it again he didnot change the old A/C belt
just i ride my car i heard a whistle with A/c on or off
i chnage the A/C belt with new one and still i have that bad whistle
how can i know if the whistle comes from the a/c belt or from another item


thanks