Heat Pump Not Cooling in Palo Alto, CA

Heat Pump Not Cooling in Palo Alto

A heat pump uses the same refrigeration cycle as an air conditioner, with a reversing valve added so one unit can heat and cool across the seasons. When a Palo Alto heat pump runs but stops cooling, we diagnose it like an AC and then check the reversing valve, which is the piece a cooling-only system does not carry.

Palo Alto sits in a mild marine-influenced zone with heavy summer morning fog, so the cooling load is lighter than the inland Tri-Valley. The housing here is distinctive, and it shapes the failures we see. The Eichler tracts in Greer and Greenmeadow run multi-head ductless heat pumps, because the post-and-beam ceilings rule out ducts, and a multi-zone system has more components that can fail per head. The older Spanish-revival stock in Old Palo Alto and Crescent Park often has newer high-efficiency equipment retrofitted into heritage layouts, which is its own diagnostic picture.

In almost every case, a heat pump that runs but will not cool has one failed part, not a dead system. On a multi-head Eichler install, that often means isolating which head or which zone is the problem rather than condemning the whole system. We find it, then put the fix and the price on a written estimate before any work.

Common causes

Reversing valve stuck in heat mode. This is the failure a plain AC cannot have. The valve that switches the system between heating and cooling can stick or its solenoid coil can fail, leaving the unit running in heat when you call for cool. We read line temperatures across a mode change to confirm it. On multi-head systems the valve is in the outdoor unit, so a valve fault affects every head at once, which helps us isolate it quickly.

Refrigerant leak or low charge. Low refrigerant from a slow leak makes the system run constantly and cool weakly. On ductless installs the common leak points are the flare connections at the indoor heads. We pressure-test, locate the leak, repair the connection, and weigh in the correct charge. A leak that is not actually found and fixed comes back the same way, so we do the repair instead of a top-off.

Dirty outdoor coil. A condenser coil packed with dust and debris cannot reject heat, and the house never cools even though the unit runs. It is the cheapest item to fix. We wash the coil properly, clear the airflow path, and recheck operating pressures to confirm the system recovers before chasing anything more involved.

Failed capacitor or contactor on conventional units. On the ducted and single-zone heat pumps in the older stock, a weak run capacitor leaves the compressor or fan straining, and a pitted contactor fails to power the outdoor unit, so it runs without cooling. We carry both and meter the capacitor rather than guessing. Variable-speed ductless units use inverter boards instead, which we diagnose differently.

Frozen indoor coil from low airflow. A dirty filter on a ducted system, or clogged head filters on a ductless system, drops airflow until the coil ices over and stops cooling. You will see weak airflow and sometimes water dripping as it thaws. We thaw the coil, clear the filters or find the airflow restriction, and fix the cause so it does not re-freeze.

Thermostat or controller in the wrong mode. Heat pump thermostats and ductless wall controllers drive the reversing valve, and a wrong mode, a mis-set controller, or a wiring error after a thermostat swap can run the system in heat while you ask for cool. We verify the control configuration and the signal it is sending first, before opening equipment.

How we diagnose it

Confirm the thermostat or ductless controller is set for cooling and sending the correct reversing-valve signal, ruling out a configuration error.
On multi-head systems, isolate whether the problem is one head, one zone, or the shared outdoor unit before diagnosing components.
Read line temperatures and pressures across a mode change to verify the reversing valve is shifting into cooling.
Inspect the outdoor coil and, on conventional units, meter the capacitor and contactor; on inverter ductless units, check the control board and sensors.
Pressure-test the charge and, if low, find the leak at the flare connections rather than topping off.

$75 diagnostic, credited toward any repair over $200. You get a written quote before any work begins.

Heat Pump Not Cooling in Palo Alto: common questions

Do you service Palo Alto from out of the area, and how quickly?

We are based in San Ramon and cover Palo Alto and the South Bay. Same-day is best effort rather than a guarantee, but a no-cooling call during a warm stretch gets priority. If you have a multi-head Eichler system, tell us the brand when you call so we arrive ready to diagnose the right equipment.

My Eichler has a multi-head system and only one room stopped cooling. Is the whole thing failing?

Usually not. When a single head or zone stops cooling while others work, the problem is typically that head, its filter, or its flare connection, not the shared outdoor unit. A fault that kills all heads at once points to the compressor, the reversing valve, or the charge. We isolate which it is before recommending anything.

Summers are mild here. Is it normal for a heat pump to barely cool on a foggy day?

On a cool foggy morning the system has very little work to do, so light output is normal. The test is a warm afternoon. If the unit runs hard and still will not bring the house down on a genuinely warm day, something has failed, most often the charge, the coil, or the reversing valve, and we will diagnose it and quote the repair in writing.

Nearby and related

Heat Pump Not Cooling near Palo Alto: Menlo Park · Los Altos · Mountain View .

This is usually a heat pump installation & service in Palo Alto job. See our heat pump installation & service overview or the Palo Alto service area.