Heat pumps in Sunnyvale, Santa Clara and Cupertino work in both seasons, cooling through summer hot spells and heating from November to March, so they collect more running hours than a furnace. When one fails, the cause is usually electrical (capacitor, contactor, fan motor), a sensor or control problem in the defrost system, a reversing valve that will not shift, or a refrigerant leak. The diagnosis starts with what the system does in each mode, because a fault that shows in heating often shows in cooling too.
What makes a heat pump different
- Reversing valve. It switches the direction of refrigerant flow between heating and cooling. If it sticks, the system may only heat or only cool.
- Defrost. In heat mode the outdoor coil runs colder than the outside air. On cold, damp mornings it frosts, and the control briefly switches to cooling to melt it. That is normal; a coil that never clears is not.
- Auxiliary heat. Ducted heat pumps usually have electric strips in the air handler to help during defrost and cold starts. If they carry the load all the time, bills climb and the heat pump may not be working.
- Inverter controls. Variable-speed models use electronic boards and sensors that report fault codes, which guide the testing.
Common symptoms and what they usually mean
| What you notice | Likely cause | What it usually takes |
|---|---|---|
| Cool air in heat mode, outdoor unit running | Stuck reversing valve, low refrigerant, wrong thermostat setting | Valve and control testing, leak search |
| Outdoor coil stays covered in ice | Defrost control or sensor, outdoor fan, low charge | Defrost system testing |
| Heats only on aux, high electric bills | Compressor not starting, capacitor, contactor, lockout | Electrical diagnosis |
| Outdoor unit hums, fan does not spin | Capacitor or fan motor | Part replacement |
| Cools fine but will not heat, or the reverse | Reversing valve or its solenoid coil, thermostat wiring | Control testing |
| Error code on an inverter or ductless unit | Sensor, communication or board fault | Code-guided testing |
| Water around the outdoor unit in winter | Normal defrost meltwater, unless it freezes in the base | Clearing the drain path |
The thermostat matters more on a heat pump
Many heat pump calls after a thermostat change are setup problems, not broken parts. The thermostat has to be set for a heat pump, with the reversing valve energized in the right mode: brands differ on whether that happens in cooling (often marked O) or heating (often marked B). Get it backwards and the system cools when you ask for heat. Auxiliary heat settings matter as well, since a thermostat that calls for strips too early hides a weak heat pump and raises bills. Smart thermostats, including Sensi models, need the same configuration.
Refrigerant leaks and the compressor
Low refrigerant in a heat pump shows up in both modes: weak heat in winter, weak cooling in summer, and sometimes ice. Adding refrigerant without finding the leak only delays the next call, so the leak is located and repaired, the system is evacuated, and the charge is set to the manufacturer’s specification. Refrigerant work is done by EPA-certified technicians. Older systems that use R-22, which is no longer produced, make a major leak a bigger decision, and a failed compressor on an older unit is usually where heat pump installation comes into the conversation.
Parts and warranty
Capacitors, defrost boards, sensors and fan motors are matched to the exact model, age and warranty status of your unit. If a manufacturer parts warranty may still apply, it gets checked before you pay for the part. Repairs are backed by a warranty covering parts and labor, and you see the findings and cost factors before work begins.
Safe checks before you call
- The thermostat is on Heat, not Emergency Heat, and set a few degrees above room temperature.
- The filter at the indoor unit is clean.
- The outdoor unit is clear of leaves, plants and anything stacked against it.
- Both breakers, for the outdoor unit and the indoor air handler, are on.
Do not chip or pry ice off the outdoor coil; the fins and tubing bend easily. If it stays iced for hours, switch the system off and call.
Local notes
The coldest clear winter nights here can bring frost, and those are the mornings when frequent defrost cycles are normal. Ductless heat pumps are common in Eichler homes and additions; see ductless mini-splits and mini-split repair. In townhomes and condos the outdoor unit often sits on a balcony or roof, so tell us about access when you call. City pages: Sunnyvale, Santa Clara and Cupertino.