If the air conditioner is not behaving itself (particularly if the indoor fan is working, but the air coming off the outdoor unit is not hot in summer or is not cold in winter, it may need resetting. If you have been told a specific method for that air conditioner, use that method. Check the manual to see if it lists a method. Otherwise, switch the air conditioner off at the main power switch. For a wall hung unit this will normally be at a power point next to the indoor unit. If not it will normally be located adjacent the outdoor unit. Wait about 15 seconds after everything has gone off then turn the main power switch back on. You may need to wait up to 10 minutes for the compressor to come back on. Repeat the above checks. If it still does not seem to work, the air conditioner may be faulty, call the manufacturer's or contractor's service department. Note an occasional need to reset the air conditioner is normal, particularly on an extreme day, however a frequent need for resetting should be investigated by the service department.