A C Not Working Check this How to test and replace an Evaporator Temperature Sensor
NOS 1968-75 GM A/C AMBIENT SENSOR SWITCH Air Conditioning AC 3917359 483326. NOS 1968-75 GM A/C AMBIENT SENSOR SWITCH Air Conditioning AC 3917359 483326. GENERAL MOTORS A/C Ambient Sensor Switch. Only difference is a fiber-base, as opposed to an all metal housing.