If you see the E320 error code, there is a problem with the OLP sensor, which is part of the outdoor unit. Try resetting it by turning it off for about 30 seconds. If the problem persists, replace the temp sensor. Check with an online store for any part you need, because there are tons of them. Please, note that replacing the sensor is not an easy game for everyone, because you need to disassemble the entire unit to get to it (or the PCB).