Heat pump frequently enters defrost or stays in defrost too long, H1 or similar code logged

Safety first: Disconnect power at the outdoor disconnect before handling sensors or wiring.

Steps:

• 1. Inspect sensor placement: Ensure the defrost sensor is clipped to the correct coil tube as indicated on the unit’s wiring diagram or service label.
• 2. Check for moisture damage: Look for cracked sensor casing or water inside the sensor connection. Replace if compromised.
• 3. Measure resistance: With power off, disconnect the sensor and measure resistance. Compare to the Armstrong Air chart for the current outdoor temperature. A very low resistance (near 0Ω) suggests a shorted sensor.
• 4. Replace sensor if needed: Install a new OEM defrost sensor and secure it firmly to the coil tube.
• 5. Reset system: Restore power and monitor defrost cycles. If H1 or abnormal defrosting continues, the outdoor control board may require replacement.