Carrier HH18HA279 Defrost Sensor

When you're out on a service call for a heat pump that is "iced up" or failing to initiate a defrost cycle, the Carrier HH18HA279 Defrost Sensor is often your primary point of failure. This OEM temperature activation switch is specifically calibrated to a 65-33 degree range, naturally closing at approximately 32°F to signal the Carrier defrost control board and opening at 65°F to terminate the cycle. Engineered for heavy-duty heat pump maintenance, it features a tube-mount design that ensures direct thermal contact with the outdoor evaporator coil for precise feedback.

This genuine Carrier factory authorized part is the standard replacement defrost sensor for a wide range of Carrier, Bryant, and Payne systems, including the popular 50VT series. With a wide operating temperature range from -40°F to 150°F, it maintains accuracy in extreme winter conditions. Replacing a faulty sensor with this HVAC OEM part restores the critical sequence of operation, preventing coil damage and ensuring the reversing valve and auxiliary heat strips engage exactly when needed.

• Precise 65-33 Degree Logic: Calibrated to close at 32°F (±3°F) and open at 65°F for optimal defrost timing.
• Direct OEM Compatibility: A drop-in replacement for Carrier, Bryant, and Payne heat pumps, including models 50VT024 through 50VT060.
• Durable Tube Mount: Designed for 3/8" or 1/2" tubing to provide the most accurate coil temperature sensing.
• Rugged Environmental Resistance: Built to withstand moisture, vibration, and thermal cycling in outdoor condenser sections.

Is this sensor compatibility-limited to specific boards?
While designed for Carrier-family time and temperature defrost boards, it is the standard 10k-ohm or bimetal equivalent (depending on legacy) specified for most modern Carrier residential units.

What are the symptoms of a failing HH18HA279?
The most common signs are the outdoor unit becoming a block of ice or the system staying in defrost mode too long, leading to excessive use of expensive auxiliary electric heat.

How do I test this sensor in the field?
Perform an ohm test in an ice bath; the switch should show continuity (0 ohms) near freezing and open (infinite ohms) once warmed above 65°F.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.