Carrier HVAC Error Code 27

Error code 27 on a Carrier HVAC system means the outdoor unit size being reported to the fan coil is invalid for that application. The system's User Interface is either not communicating properly with the outdoor unit or has an incorrect size value configured. This prevents the fan coil from setting up matched-system operation correctly. The fault must be resolved by verifying communication wiring or correcting the size selection at the User Interface.

Error code 27 is a configuration and communication fault, not a safety-critical failure involving refrigerant pressure, electrical overloads, or heat. However, the system may not operate correctly or at all while this fault is active. You should not ignore it long-term, as running a system with mismatched configuration data can lead to improper operation or component strain.

If the fix is limited to correcting wiring connections or adjusting the size setting in the User Interface, labor costs are typically minimal and could range from roughly 75 to 150 dollars for a service call. If a component like the User Interface control board needs replacement, costs can rise to the 200 to 600 dollar range or more depending on the specific part and labor rates in your area. Getting a diagnostic visit from a qualified HVAC technician is the best way to determine the exact scope and cost of the repair.

Start by inspecting all communication wiring between the User Interface and the outdoor unit for loose, damaged, or reversed connections. If wiring appears intact, access the User Interface configuration menu and verify that the outdoor unit size selected matches the actual installed unit from the valid size list. If communication cannot be established after checking wiring, the UI or outdoor unit control board may require further evaluation by a qualified technician.

A simple power reset is unlikely to permanently clear error code 27 because the fault is caused by an underlying configuration or communication issue that persists through a reset. The code will return if the User Interface still lacks valid communication with the outdoor unit or if an incorrect size is still selected. The root cause must be corrected before the fault will clear reliably.