Aprilaire dehumidifier fan runs but compressor never starts

Safety first: Turn off power at the breaker and verify power is off before opening the electrical compartment. Capacitors can hold a charge; discharge safely.

• Check line voltage: Measure voltage at the dehumidifier input terminals. Ensure it matches the nameplate rating.
• Inspect capacitor: Locate the compressor run capacitor. Look for bulging, leaking, or burned terminals. Replace the Aprilaire compressor run capacitor if any damage is visible.
• Test capacitor: Use a capacitance meter to verify the µF value is within ±10% of the rating. Replace if out of range.
• Check compressor windings: With power off and wires removed, measure resistance between compressor terminals (C-R, C-S, R-S). Open circuits indicate a failed compressor.
• Replace control relay/board: If the compressor and capacitor test good but the board never sends power to the compressor, replace the Aprilaire dehumidifier main control board.