HEAT PUMP BLOWS COLD — AT 30°F OUTSIDE

#1 Settings, airflow or normal operating changes need checking first

Supporting Evidence: The complaint includes temperature variation without measured air temperatures or verified operating settings. Between-call fan operation or defrost could contribute.

Counterevidence: A 2°F room-temperature shortfall remains unexplained. Normal-feeling air does not establish adequate heat delivery; filter or airflow restrictions also remain possible.

#2 Heating demand exceeds delivered capacity, or backup heat is unavailable when required

Supporting Evidence: Long runtime and room-temperature drift warrant checking recovery, installed capacity and backup-heat configuration.

Counterevidence: There is no verified backup-heat call or output measurement. Some systems intentionally lock out backup heat at this temperature; 30°F alone identifies no fault.

#3 Refrigerant, compressor, defrost or reversing-valve fault

Supporting Evidence: Inadequate heating can occur with these faults. Persistent cold air, failed recovery or uncleared ice would strengthen the need for service.

Counterevidence: Those conditions have not been verified. One register temperature cannot separate these faults from airflow, controls, duct losses or backup-heat behavior.

? Why does my heat pump blow cold air when it's cold outside?

Heat-pump supply air can feel cooler than furnace air while still adding heat to the room. Defrost can also temporarily change the air temperature. But persistent inadequate heating needs investigation. Feeling cool does not prove a fault, and feeling warm does not prove sufficient capacity. Check the operating mode, room-temperature trend and equipment-specific guidance before naming a component.

? What temperature should the air from my heat pump registers be?

There is no universal register-temperature pass/fail number for 30°F outdoors. Carrier gives roughly 85–100°F as a general heating illustration, not a specification for this unidentified system. Supply temperature depends on indoor entering-air temperature, airflow, equipment stages, backup heat and duct losses. Record supply and accessible return-air readings with operating conditions. A qualified technician must interpret them against the exact equipment's performance data. One register reading cannot confirm charge, capacity or valve operation.

? When should auxiliary heat come on — and how do I know if it's working?

That depends on the equipment, home, thermostat and configured controls. There is no universal requirement for auxiliary heat to start at 30°F. Backup heat may be electric resistance or a furnace in a dual-fuel system. An AUX display is an observation of controller status, not proof that the backup source delivered its rated heat. Identify the installed backup source and controls before interpreting it. Emergency heat can provide temporary backup during a malfunction when the owner's instructions permit it; it is not a diagnosis.

? Is it normal for a heat pump to blow cool air during defrost?

It can be. Defrost temporarily reverses refrigerant flow to warm the outdoor coil; steam may appear and the outdoor fan may stop. Backup heat can reduce the indoor temperature change when fitted and operating. Duration and control behavior depend on the model and conditions, so no universal 5–15-minute clock test identifies a fault. Record whether heating recovers. Persistent cold air, failed recovery or ice that does not clear needs professional assessment, not an assumed reversing-valve diagnosis.