Heat pump not defrosting — San Francisco, California
Heat pumps naturally build frost on the outdoor coil in cold weather, and they run automatic defrost cycles every 30–90 minutes to melt it off. When defrost fails, ice encases the entire outdoor unit, blocking airflow and destroying efficiency — you'll notice lukewarm air from the vents and the compressor running constantly. Common causes are a faulty defrost control board or timer, a stuck reversing valve (which flips the system to cooling mode temporarily to defrost), a bad defrost thermostat or sensor, or a refrigerant leak that alters coil temperature. An HVAC technician can diagnose the failed component, replace the board, sensor, or valve, and verify proper defrost cycling before ice damages the compressor.
Why this is common in San Francisco
The cool, foggy maritime climate means central AC is rare and rarely needed, so HVAC work centers on heating efficiency, ventilation, and increasingly heat-pump retrofits driven by Title 24 energy rules. Older homes often have undersized or outdated heating systems requiring careful upgrades.
Who to call
For this problem in San Francisco, call a: HVAC Technician
Find a HVAC Technician in San FranciscoSymptoms to look for
- Thick layer of ice on the entire outdoor heat pump unit
- Lukewarm or cool air blowing from vents when set to heat
- Outdoor unit fan runs constantly but never switches to defrost mode
- Higher than usual electricity bills during heating season
- Compressor makes laboring or unusual sounds under heavy ice load
Emergency Service in San Francisco
Emergency home services in San Francisco are available 24/7 at premium rates — expect $150–$300+/hour for after-hours plumbing or electrical, the highest tier in the US. Response times average 45–90 minutes given hilly terrain and parking scarcity. Always verify an active CSLB license and proper DBI permits.