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