If your Mitsubishi MR SLIM air conditioner is flashing a three times, this indicates that the unit has encountered an error code. This could be due to a variety of problems such as power interruption, faulty wiring or blocked filters. In order to determine why your unit’s light is blinking 3 times and fix the problem, it is important to first consult your owner’s manual for troubleshooting tips or contact a local HVAC technician for assistance.