Lennox Furnace Error Code E308

E308 indicates a compressor low voltage fault detected by the LSOM, or Load Shed Output Module, in your Lennox system. The control system has determined that voltage to the compressor has dropped below safe operating levels. This code causes a protective shutdown to prevent compressor damage. A technician should measure voltage at the outdoor unit and trace the supply path to find the source of the voltage drop.

The E308 fault is a protective code that typically shuts down the compressor to prevent damage, so the system is generally not running the compressor while the fault is active. You should not attempt to repeatedly reset the system and force compressor operation without resolving the underlying voltage issue. Running a compressor under low voltage conditions can cause overheating, winding failure, and permanent compressor damage.

Resetting the system may temporarily clear the E308 fault and allow the system to attempt operation again. However, if the underlying low voltage condition still exists, the fault will return once the compressor tries to start. A reset without a repair does not fix the problem and repeated compressor start attempts under low voltage can accelerate component wear.

Some basic checks, such as inspecting for a tripped breaker or a visibly damaged disconnect, can be performed by a homeowner. However, diagnosing low voltage conditions requires a multimeter and work near live electrical components, which carries serious safety risks for those without electrical training. Most causes of E308 require a qualified HVAC technician to properly diagnose and repair.

Repair costs vary widely depending on the root cause. A simple fix such as tightening connections or replacing a contactor could cost between $75 and $250 in parts and labor. If the issue is a failing transformer, expect costs in the range of $150 to $400. If utility voltage is the source, an electrician may be needed to address the service panel or incoming supply, which can range from $200 to $600 or more depending on the scope of work.