i see that ed morad sells the actuators online, but how do i know what model # to get??

The temp actuators are mounted on either side of the heater box; and can be electric or vacuum operated. You can get the number for the correct one from the parts dept of your GM dealer(give them the last 8 digits of your VIN). AC Delco's part# for the actuators: 15-73627

Parts info from AC Delco's site: Parts List