Heat Pump Not Cooling in Mountain View, CA

Heat Pump Not Cooling in Mountain View

A heat pump cools on the same refrigeration cycle as an AC and adds a reversing valve to switch into heating for winter. When a Mountain View heat pump runs but will not cool, we diagnose it the way we would any AC that lost cooling, and we check the reversing valve as the heat-pump-specific suspect.

Mountain View has genuinely mild summers, with design cooling around 88 degrees and heavy marine-layer fog most summer mornings. That climate means many homes here, especially in Old Mountain View, were built with heat only and had AC or a heat pump added later. Retrofit systems and ADU mini-splits are common, and that history matters: a marginal charge or a tight duct run on an added-on system shows up as weak cooling the moment a warm afternoon burns off the fog.

A heat pump that powers on and moves air almost always has a sound compressor and fan, the costly parts. The real problem is one component, often a worn capacitor or a slow leak, sometimes a frozen indoor coil behind a tight duct or a thermostat configured for the wrong mode. We find the actual fault, write the price on the estimate, and tell you honestly whether repair or replacement makes more sense.

Common causes

Reversing valve stuck in heat mode. The reversing valve lets a heat pump cool in summer and heat in winter. When it or its solenoid sticks, the system keeps running in heat and blows warm air on a cooling call. We confirm with line-temperature readings and by watching the valve shift on a mode change, then replace the solenoid coil or valve body that failed.

Low refrigerant from a leak. On retrofit and mini-split systems common here, a slow leak at a flare or brazed joint produces weak cooling, a frosted suction line, and long run times. We measure superheat and subcooling, find the leak, repair it, and recharge to spec. We don't add refrigerant to a system that is leaking it back out.

Frozen indoor coil from tight retrofit ductwork. Old Mountain View starter homes often have tight original ducts that were never sized for cooling airflow. Add a dirty filter or a weak blower and the indoor coil ices over, killing cooling. We thaw the coil and address the airflow restriction; sometimes the real fix is a duct or filter-grille correction rather than a part.

Failed run capacitor or contactor. The capacitor starts the compressor and outdoor fan; the contactor powers the outdoor unit. A weak capacitor leaves the fan stalled or the compressor tripping, and a pitted contactor drops power intermittently. Both are common, inexpensive, and stocked on the truck.

Dirty outdoor coil. A heat pump sheds the home's heat through its outdoor coil. Marine-layer humidity and yard debris foul the fins over time, and a clogged coil cannot reject heat, so the unit runs without cooling. We clean the coil and confirm the temperature split recovers.

Mini-split fault on ADU and home-office heads. Many Mountain View ADUs and converted garages run a single ductless head. A blocked condensate sensor, a dirty blower wheel, or a communication fault between the head and the outdoor unit can stop cooling on these systems. We read the unit's fault code, clean the wheel, and check the line-set connections.

How we diagnose it

Confirm the thermostat or mini-split controller is calling for cool and the reversing-valve signal is correct.
Verify the outdoor unit starts: capacitor, contactor, compressor, and condenser fan.
Read refrigerant pressures, superheat, and subcooling to separate a leak from a valve problem.
Inspect the indoor coil, filter, and any tight retrofit ductwork for the airflow restrictions that freeze coils.
On mini-splits, pull fault codes and check the blower wheel and line-set connections, then verify the cooling split.

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

Heat Pump Not Cooling in Mountain View: common questions

How do you handle Mountain View calls from a San Ramon base?

We run the Peninsula and South Bay regularly, including Mountain View, Palo Alto, and Los Altos. We book Mountain View calls promptly and give you a real arrival window rather than a vague all-day promise. Call (925) 999-4095 and we will tell you honestly whether same-day is open.

Our Mountain View house had AC added to an older furnace. Does that make a no-cool problem harder to fix?

Not harder, just a different first check. A lot of Old Mountain View homes had cooling added to original ducts that were sized for heat only, so weak airflow and frozen coils are more common than on purpose-built systems. We measure the airflow and the charge, and if the ducts are the bottleneck we tell you that instead of selling you a part that will not solve it.

My ductless mini-split in the ADU runs but will not cool. What now?

On a single-head mini-split, no cooling usually means low refrigerant from a flare leak, a dirty blower wheel, or a fault between the indoor head and the outdoor unit. Most units display a fault code that points us straight to it. We diagnose for $75, credited toward the repair when it is over $200, and identify the cause before any parts.

Nearby and related

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

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