Lennox Air Conditioner Error Code 15

Error code 15 means the mode jumper on the TSC5 two-speed control board is not in place or is improperly seated. The TSC5 requires a physical jumper bridging the correct set of pins to identify which operating mode the system is configured for. Without it, the control board cannot function and the system will not run normally. A technician needs to locate, seat, or replace the jumper to resolve the fault.

Error code 15 indicates the TSC5 control board cannot determine its operating mode, which means the system is unlikely to operate correctly or at all in this state. Attempting to run the system without resolving the jumper issue could lead to improper compressor or fan behavior. The system should be kept off until the jumper is correctly installed and the fault is cleared.

A reset alone will not clear error code 15 because the underlying hardware condition, the missing or improperly seated mode jumper, must be corrected first. The TSC5 will continue to detect the absent jumper every time the system powers up and will regenerate the fault. The jumper must be physically placed and secured on the correct pins before the error will clear and normal operation can resume.

If you are comfortable working around electrical components with the system powered down, visually inspecting the TSC5 board for a missing or loose jumper is a reasonable first step. However, correctly identifying the right pin set for your specific mode of operation requires familiarity with the TSC5 control board layout. If the jumper is missing or you are unsure which pins to bridge, it is best to have a qualified technician handle the repair to avoid incorrect configuration.

If the jumper is simply loose or displaced, the repair cost covers only a service call, typically in the range of $75 to $150 depending on your region and technician. If the jumper is lost and needs replacement, the part itself is inexpensive, usually a few dollars, but labor charges still apply. If the TSC5 board itself requires replacement due to damage, costs can rise to the $300 to $600 range including parts and labor.