First of all, check the breakers. If you notice the breaker is off or tripped try this: Make sure the breaker is all the way flipped off and flip it back on if the breaker trips or flips off.  If the breaker stays on and the unit is still not working,  call us immediately. Second, flip off all breakers to the air conditioner and check to see if the thermostat has batteries. Make sure no battery acid leaked into the thermostat. If no battery acid is present replace the batteries with new ones and turn all breakers back on. Thirdly, flip off all breakers to the air conditioner and check to see if the unit has a safety float switch in line with the drain line. If your unit has the float switch remove the float and check if the water is in the overflow space. If no water is present give us a call immediately.