A/c starts off very cold when first engaged, even on a hot day but after aprox 60-180 seconds it warms up to ambient air temp. If I turn off the A/C for 20 minutes or so I can get it do run cold for that 1-3 minutes agin otherwise stays warm. Is this a cluth or thermal expansion valve problem? How would I troubleshoot this?

john in ATL (starting to get pretty hot)