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This sounds like it could be a bad thermostat. Have you tried bypassing the thermostat?
Turn power off to furnace or air handler. Take front part of thermostat off the wall loose from back section where all the wiring is. We will take the wire off the R terminal, Y terminal, and G terminal and twist the metal ends together, then turn power back on. See if AC now works.
RC and R
Is outside unit running?
Is the suction line cold to the touch? The suction line is the larger of the two copper lines going into unit and covered with black foam.
Sounds like either compressor is not running or unit has lost some or all of it's charge.
That would be a bad thermostat most likely. Since you have the thermostat off the wall, take the white wire off the W terminal, see if heater stops.
Is furnace running?