Heat Pump Not Cooling in Hillsborough, CA

Heat Pump Not Cooling in Hillsborough

Hillsborough summers are mild, rarely past the mid-80s, so a heat pump that quietly stops cooling can go unnoticed for a week or two before the house actually gets uncomfortable. By the time someone calls us, it is usually one of two things: a part on the cooling side has failed, or the system is locked in heating mode. A heat pump cools by reversing its refrigerant flow, so it heats and cools through the same loop. When it heats fine but will not cool, the cooling-specific hardware is almost always where the fault sits.

Most Hillsborough homes run several independent systems, one per floor or wing, so the symptom often shows up in just part of the house. That narrows the search. A single zone going warm while the others hold tells us the problem is local to that condenser and air handler, not a house-wide failure. We can isolate the affected system instead of chasing the whole property.

This is rarely a dead unit. A stuck reversing valve, a failed capacitor, or a slow refrigerant leak are single-component faults, each with a defined fix and a number we can put on a written estimate before any work starts.

Common causes

Reversing valve stuck in heat mode. The reversing valve is what switches a heat pump between heating and cooling. When it sticks or its solenoid fails, the unit keeps running but blows warm air on a cooling call. We check the valve's position electrically and by temperature across the lines, then replace the solenoid or the valve depending on what tests bad. On the older estate equipment up here we see this more than people expect.

Low refrigerant from a leak. If the charge has dropped, the system runs but cannot pull heat out of the house, and you get weak, lukewarm air. We don't simply top it off. We find the leak first, usually at a flare, a service valve, or the coil, with electronic detection or nitrogen pressure test, then repair, evacuate, and recharge to spec. On the long line-set runs common in spread-out Hillsborough homes, fittings and joints are the usual culprits.

Dirty or blocked outdoor coil. These lots are wooded and tree-shaded, so condenser coils pack with leaf debris, pollen, and dust. A clogged coil can't reject heat, head pressure climbs, and cooling capacity falls off. We clean the coil, clear the surrounding clearance, and recheck pressures. It is one of the cheaper fixes and an easy one to miss if nobody inspects the outdoor unit.

Failed capacitor or contactor. The run capacitor starts the compressor and fan; the contactor switches power to them. When either fails, the unit may hum, trip, or run the fan without the compressor, so air moves but never gets cold. We test both with a meter and carry common sizes on the truck, so this is frequently a same-visit repair.

Frozen indoor coil from low airflow. A dirty filter, a failing blower, or a closed-up return starves the indoor coil of airflow, and it ices over. Once it freezes, almost no cold air reaches the rooms. We thaw it, find why airflow dropped, and fix that. On multi-zone estate systems a stuck zone damper can choke airflow to one coil, which is worth checking here specifically.

Thermostat or zoning control in the wrong mode. With several thermostats and a zoning board in one house, it is easy for one zone to sit in heat mode or for a control board to drift. We verify each thermostat's mode and call, confirm the board is sending the cooling signal and energizing the reversing valve, and rule out a control fault before touching the refrigerant side.

How we diagnose it

Confirm which zone or system is affected and verify that thermostat is actually calling for cooling, not stuck in heat or auto.
Check the reversing valve position by line temperature and energize its solenoid to confirm it shifts on a cooling call.
Read suction and head pressures against the outdoor temperature to see whether the charge is low or the coil is rejecting heat poorly.
Test the capacitor and contactor, and inspect the outdoor coil for leaf and tree debris on these wooded lots.
Inspect the indoor coil and filter for ice and airflow restriction, and check the zoning dampers for the affected wing.

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

Heat Pump Not Cooling in Hillsborough: common questions

Do you actually cover Hillsborough, given you're based in San Ramon?

Yes. We're based in San Ramon but run the Peninsula and South Bay regularly, including Hillsborough's 94010. Call (925) 999-4095 and we'll give you an honest window. Same-day is best-effort, not guaranteed, but a no-cool call in summer gets priority routing.

Our summers are mild here, so is a heat pump that won't cool even worth fixing right away?

It depends on how the house is used. Hillsborough rarely gets brutally hot, but a large estate with western exposure or a finished upper floor can still run uncomfortable on the warmer afternoons. The fix is usually a single part, so it's rarely an expensive call, and leaving a low-charge or frozen system running can damage the compressor, which is the expensive part.

It heats fine in winter but won't cool in summer. What does that tell you?

That the heating side and the compressor are healthy and the problem is cooling-specific. The two most likely causes are a reversing valve stuck in heat mode or low refrigerant from a leak. Both are diagnosable in one visit. Our diagnostic is $75, credited toward the repair if it runs over $200.

Nearby and related

Heat Pump Not Cooling near Hillsborough: Menlo Park · Palo Alto .

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