Hello , My A/C is only cooling when I’m driving, but if I get to an stop light or at idle the A/c blows warm air. I did notice that my fan does not kick in at high speed it only does at a steady low speed. My engine does not heat up.. I will like to know how can I trouble shoot this so I can get to the bottom of this before taking it to a mechanic any help would be appreciated since I live in Miami and A/C is a “Big necessity”.

Regards
Rick E.