A sequencer is an automatic control device that stages the operation of multiple heating elements in a furnace, turning them on in timed intervals to avoid electrical overload. Sequencers prevent demand spikes that would exceed utility service limitations. These devices use thermal elements that expand at different rates to activate heating stages sequentially over 30 to 60-second intervals.
Technical Operation
Sequencers contain bimetallic strips that heat from the first-stage heating element. As temperature rises, successive strips bend and close contacts for second, third, and additional stages. This staging process prevents single large power draws and distributes electrical demand across multiple heating cycles. Residential systems typically use sequencers rated for 40-amp service or less.
Reliability and Maintenance
Sequencers provide cost-effective load management without complex control circuits. However, stuck or sluggish bimetallic elements can cause heating stages to activate simultaneously, tripping circuit breakers. Annual furnace service includes sequencer testing to verify proper staging intervals. Replacement sequencers cost between 150 and 250 dollars including labor.