A customer reports that their cold climate heat pump is not providing adequate heating when the outdoor temperature drops to -25°C, even though the system is rated for operation down to -30°C. Upon inspection, the technician observes frequent defrost cycles and a noticeable drop in discharge air temperature indoors. What is a probable cause?

Question: A customer reports that their cold climate heat pump is not providing adequate heating when the outdoor temperature drops to -25°C, even though the system is rated for operation down to -30°C. Upon inspection, the technician observes frequent defrost cycles and a noticeable drop in discharge air temperature indoors. What is a probable cause?

Answer options: ✅ The outdoor coil is accumulating excessive frost, leading to frequent and ineffective defrosts.

• The indoor coil is becoming iced over due to insufficient airflow.
• The auxiliary heat strips have failed and are not energizing when required.
• The refrigerant charge is critically low, impacting system capacity at extreme temperatures.

Correct answer: The outdoor coil is accumulating excessive frost, leading to frequent and ineffective defrosts.

Explanation: In extremely cold temperatures, even cold climate heat pumps can struggle with excessive frost formation on the outdoor coil. Frequent, ineffective defrosts indicate the system is spending too much time defrosting rather than heating, leading to reduced comfort. While other issues are possible, frequent defrost on 'cold climate' unit at 'its lowest rated temp' is a strong indicator of outdoor coil frosting issue.