Lennox Heat Pump Error Code DS2:FastFlash / DS1:ON

This code indicates a discharge line temperature lockout. The control board detected high discharge line temperature conditions five times during a single call for heating or cooling (Y1 demand) and shut down the compressor to prevent damage. The system will remain locked out until it is manually reset and the underlying cause is corrected.

The lockout is a protective measure designed to prevent compressor failure. The compressor will not run while the system is in lockout, so continued operation is not immediately possible. Attempting repeated resets without addressing the cause can accelerate compressor wear and lead to a much more expensive failure. It is best to have the system diagnosed before resetting it multiple times.

After resetting the fault, the technician should check system refrigerant charge using manifold gauges, inspect and measure airflow across both the indoor and outdoor coils, and examine the discharge line temperature sensor and its wiring for damage or loose connections. Operating pressures, superheat, and subcooling values should all be compared to the unit's specifications to identify whether a refrigerant or airflow issue is responsible for the repeated high-temperature events.

A reset, either by cycling 24V power to the board or shorting the TEST pins for 1 to 2 seconds, will clear the lockout and allow the system to restart. However, if the root cause such as low charge, blocked airflow, or a bad sensor is not fixed, the system will accumulate five more discharge temperature faults and lock out again. The reset is a diagnostic starting point, not a fix.

Repair costs depend heavily on the root cause. Airflow-related fixes such as filter replacement or coil cleaning are relatively inexpensive, typically in the range of $50 to $200 including a service call. Refrigerant recharge with leak detection can range from $200 to $600 or more depending on the refrigerant type and leak location. Sensor replacement generally falls in the $100 to $300 range, while compressor replacement is the most costly outcome, often ranging from $1,200 to $2,500 or higher.