Lennox Furnace Error Code E306

E306 on a Lennox furnace indicates a compressor open run circuit, meaning the electrical circuit powering the compressor's run winding is not completing. The LSOM or control board detects no current flow through the compressor and shuts the system down to prevent damage. This is most often caused by the compressor overheating and tripping its internal thermal overload protector. Supporting causes include a failed outdoor fan motor, abnormal refrigerant pressures, or a dirty condenser coil.

A reset may temporarily clear the error code, but it will return if the root cause is not addressed. If the compressor tripped due to overheating, it needs sufficient cool-down time before the internal thermal overload will reset and allow normal operation. Simply power cycling the unit without diagnosing the underlying issue risks repeated thermal trips, which can shorten compressor life significantly.

Repair costs vary widely depending on the root cause. Cleaning a blocked condenser coil or replacing an outdoor fan motor typically runs in the range of $150 to $450 in parts and labor. Refrigerant-related repairs depend on the type of refrigerant and the amount needed. Compressor replacement is the most expensive outcome, generally ranging from $1,200 to $2,800 or more depending on the unit size, refrigerant type, and local labor rates.

Some basic steps are safe for a knowledgeable homeowner, such as inspecting the outdoor unit for debris blocking the condenser coil or confirming the outdoor fan is spinning. However, checking refrigerant pressures requires certified EPA 608 credentials and professional gauge equipment. If the compressor itself needs replacement, that work must be performed by a licensed HVAC technician due to the complexity and refrigerant handling requirements.

No, you should not attempt to force the system to run while E306 is active. The error indicates the compressor's protective circuit has opened, and bypassing this protection can cause permanent compressor damage or create an electrical hazard. Leave the system off and allow it to cool down fully before attempting a restart or calling a technician.