One major sign that an AC compressor has gone bad and needs replacement is when the air conditioner is blowing out warm air. The AC compressor allows the air conditioner to produce cool air by pumping refrigerant throughout the unit, so when it stops working, the air coming out of the vents is just recycled from outside.
There are a few ways to test the effectiveness of the AC compressor and troubleshoot any possible problems. First, turn the thermostat down to a very low temperature to see if the unit will start on its own. If the unit located outside does kick in, listen to it to determine if its sound has changed. If the fan is the only sound, there is likely a problem with the air compressor.
To fix the issue, turn off the air conditioner's circuit breaker, wait a few minutes and turn it back on. Next, check the service unit outside to make sure that it's on. If this still doesn't fix the problem, check the fan and the AC compressor condensing coil to make sure that there are no obstructions preventing them from working properly. If the unit is clear and resetting the circuit doesn't work, the AC compressor may need a complete replacement.