Sounds like either the coolant temperature sensor is
bad or the wiring going to the sensor has a bad
connection. When the computer stops receiving a
signal from the coolant temperature sensor it
assumes the engine is overheating to prevent
engine damage. Since the air conditioning adds an
additional heat load to the cooling system the
computer disables the air conditioning. The fact
that the temperature gauge on the dash is not
working also points to the coolant temperature
sensor. When replacing the sensor get an AC Delco
sensor. GMs don't like aftermarket coolant
temperature sensors for some reason. Hope that
helps! Jim
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