1995 Chevy Corvette runs hot in traffic with AC on

While I am in traffic my water temp climbs to 240 wth a/c on, I turn off everything get out of traffic drive and temp goes back down to normal I have checked thermostat, replaced coolant, bled thermo housing, both fans are running with ac on it does not run hot in traffic with a/c off what am I missing. I do have the edelbrock intake with a chip but the computer has been reset for them. The problem started two nights ago I was in bumper to bumper traffic I looked down and temp was 257