At MRCOOL, we don't expect you to have problems with your unit, but if you ever do see an error code, it's good to at least have some idea of what is going on. Here is what you need to know about the E3 Error Code. MRCOOL Phone Number: 270-366-0457 List of possible MRCOOL Error Codes: E0 - Indoor unit EEPROM parameter error E1 - Indoor / outdoor units communication error E2 - Zero-crossing signal detection error E3 - Indoor fan speed has been out of control E4 - Indoor room temperature sensor T1