Heat Pump Repair from a Licensed Silicon Valley HVAC Contractor
The reversing valve is the part that distinguishes a heat pump from an AC. It is a four-way solenoid valve that flips the refrigerant flow direction so the indoor coil acts as either evaporator (cooling) or condenser (heating). Most failures are not the valve itself — it is the small pilot solenoid that sits on top, energized by 24VAC during a heating call. We diagnose by listening for the click and measuring solenoid coil resistance (typically 11-15 ohms on Mitsubishi and Daikin, 14-18 on Carrier). When the valve mechanically sticks, you can sometimes free it with a sharp tap on the body during the changeover. When it fails internally — slide leakage past the seats — it must be replaced, which means refrigerant recovery, valve cut-out, brazing in the new valve under nitrogen flow, deep vacuum to 500 microns, and weighed-in factory recharge. Total job runs $850-$1,800 and takes 4-6 hours.
Defrost cycle problems are the second-most-common heat pump call. When the outdoor coil drops below freezing during heat operation, it accumulates frost that must be melted off periodically — the system reverses to AC mode briefly, runs the compressor and indoor blower stops, the outdoor coil heats up, ice melts, then it switches back to heat. The cycle is initiated by either a time-and-temperature board (older Carrier, Trane, Goodman) or a demand-defrost board that uses outdoor coil temp delta (Mitsubishi Hyper-Heat, Daikin Aurora). Failures: defrost sensor (10K thermistor) opens or shorts, defrost board capacitor fails, contactor for reversing valve solenoid pits, or the timer chip itself fails on older boards. Diagnosis uses a multimeter on the sensor and an oscilloscope or LED test light on the board outputs. Most defrost board replacements run $340-$720 with a 30-60 minute install.
Low-temperature performance complaints are different from outright failure. A heat pump that ran fine last winter but seems weak this year on a 35°F morning may have lost refrigerant charge gradually (you do not "run out" — you slowly lose subcool), may have a failing compressor that has lost about 15-20% of its pumping capacity (visible as low suction pressure with normal superheat), or may simply be a low-temp-rated unit hitting its capacity floor. Mitsubishi Hyper-Heat MXZ-SM48NAMHZ rated for 100% capacity at 5°F is one story; an older 13 SEER non-cold-climate Goodman heat pump rated for 65% capacity at 17°F and falling off a cliff below that is another. We measure outdoor temp, refrigerant pressures, supply air temp, and calculate actual capacity output, then compare to manufacturer expanded performance tables. Sometimes the answer is a $400 charge correction; sometimes it is "this equipment is undersized for cold-snap performance, here are upgrade options."
Other heat-pump-specific repairs we run regularly: crankcase heater replacement ($120-$240) — the small belly band around the compressor that keeps refrigerant from condensing in the oil sump during overnight cold; base pan heater on Mitsubishi Hyper-Heat units ($180-$320) — prevents ice damming in the unit base during long cold periods; outdoor unit drain hole clearing on cold-climate units ($60-$120) — Mitsubishi recommends drilling additional drain holes in cold-climate installs which retrofitters often skip; suction line accumulator failure (rare, $400-$700); and ECM outdoor fan motor module replacement ($380-$680) — the variable-speed fan motors on premium heat pumps fail at the controller more often than the motor itself.
What's Included in Every Heat Pump Repair Job
- EPA Section 608 universal certification for R-410A, R-32, R-454B refrigerants
- Reversing valve diagnosis: solenoid coil testing, line temperature analysis
- Defrost cycle observation and board diagnostics
- Refrigerant pressure and subcool/superheat measurement in heating mode
- Capacity calculation against manufacturer expanded performance tables
- Crankcase and base pan heater testing on cold-climate equipment
- OEM parts where available; specialty parts for Mitsubishi Hyper-Heat and Daikin Aurora stocked
- 1-year labor warranty on every repair
- Photo documentation and reading log on invoice
Common Heat Pump Repair Issues We Resolve
Heat pump blows room-temp air on heat call
Cause: Reversing valve stuck in cooling mode, low refrigerant in heat mode, failed thermostat reversing logic
Fix: Solenoid coil test, line temp analysis — valve replacement $850-$1,800, charge correction $400-$1,100
Outdoor coil ices over and stays iced
Cause: Defrost board failure, defrost sensor open, failed reversing valve preventing defrost reversal
Fix: Sequential defrost diagnostic — board $340-$720, sensor $180-$320
Heat output weak on cold mornings only
Cause: Equipment hitting capacity floor below rated outdoor temp, slow refrigerant leak, compressor wear
Fix: Capacity calc vs manufacturer table; charge correction or replacement consult
Compressor won't start on cold morning
Cause: Failed crankcase heater allowed oil to absorb refrigerant; compressor sees liquid slugging on startup
Fix: Crankcase heater replacement $120-$240; compressor protection diagnostic
Loud "whoosh" then heat stops every 60-90 minutes
Cause: Normal defrost cycle (heat pump reverses briefly to melt outdoor frost) — not a failure
Fix: Education only; document expected behavior
Mitsubishi Hyper-Heat shows error code P8 or P5
Cause: P8 = compressor temp; P5 = outdoor unit communication. Often refrigerant or wiring related
Fix: Manufacturer error code lookup, refrigerant or wiring repair — $250-$1,200
Our Heat Pump Repair Process
Same-Day Dispatch
Standard 1-2 hour response Palo Alto through San Jose; emergency response 1-3 hours after-hours.
Heat-Mode Diagnostic
Refrigerant pressures in heat mode, line temperatures at reversing valve, defrost sequence observation, error code retrieval from controller.
Quote
Flat-rate written quote before any work. Diagnostic waived when repair approved.
Repair
Most reversing valve and defrost board work completed in 4-6 hours single visit. Refrigerant work follows EPA 608 — recovery, repair, vacuum, weighed-in recharge.
Verification
Multi-cycle heat and cool mode test, defrost cycle observation, line temp re-verification, walkthrough.
Heat Pump Repair Pricing in the Bay Area
Typical heat pump repair pricing in our Silicon Valley service area runs $189 – $1 800 per repair. Most jobs complete in 1-3 hours for most repairs; reversing valve or compressor 4-6 hours.
Every quote is flat-rate and provided in writing before work begins. Diagnostic fees are waived when repair is approved. We never use time-and-materials billing surprise pricing.
Local Context: Heat Pump Repair in Silicon Valley
Heat pump installations in the Bay Area have roughly tripled since 2021 due to stacked incentives (federal IRA 25C $2,000 + TECH Clean California $1,000-$3,000 + PG&E rebates + SVCE/PCE rebates). That means the installed base of heat pumps requiring repair is rapidly aging into the 3-7 year window where reversing valves, defrost boards, and outdoor fan motors start failing. We see Mitsubishi MXZ-SM48 and Daikin Aurora units throughout Palo Alto, Menlo Park, and Mountain View — many tied to solar PV systems and SVCE/PCE all-electric rate plans. Bay Area design temperature (30-35°F) is generally above the capacity cutoff of even older non-cold-climate heat pumps, but the low-30s mornings 15-30 times per winter expose marginal performance and trigger heating repair calls. The "shoulder season" April-October when systems sit in cooling mode often masks reversing valve degradation that only shows up on the first heating call in November.
HVAC Brands We Service for Heat Pump Repair
Heat Pump Repair FAQ
My heat pump worked last winter but is weak this year — what changed?
Three usual suspects in order of likelihood. First: gradual refrigerant loss. Heat pumps lose subcool slowly through micro-leaks at flare fittings or schrader cores; you do not notice until heat output drops 10-15%. Second: compressor wear. After 8-12 years compressors lose pumping efficiency, visible as low suction pressure and weak supply air temp. Third: outdoor unit fouling. A coil packed with debris from Bay Area pollen and oak duff loses heat-transfer capacity. Diagnostic is fast and the fix is usually $400-$1,100.
Why does my heat pump make loud noises and blow cold air every hour?
That is the defrost cycle and it is normal. Every 30-90 minutes during heat operation in cold weather (under about 40°F), the system reverses to AC mode briefly to melt frost off the outdoor coil. The "whoosh" is the reversing valve actuating, the cold air is the indoor coil briefly acting as evaporator, and after 4-10 minutes the heat returns. Smart heat pumps (Mitsubishi Hyper-Heat, Daikin Aurora) use demand defrost so the cycles are shorter and less frequent — only when actually needed.
How do I know if my reversing valve is bad?
Two patterns. First: cooling works fine but heat call produces room-temp air — valve stuck in cool mode, won't flip. Second: heat works fine but cool call produces warm air — valve stuck in heat mode. Confirmed with line temperature measurement at the valve body during a mode change (one line should warm and one should cool within 30 seconds of the changeover). We also measure 24VAC at the solenoid coil — if voltage is present and the valve does not actuate, it is mechanical failure.
Is it worth repairing an old heat pump or should I replace?
Useful test: heat pump age × major repair cost > $5,000 = lean toward replacement. A 14-year-old non-cold-climate heat pump with a $1,400 reversing valve repair is a borderline case; with TECH Clean California rebates ($1,000-$3,000) and IRA 25C credit ($2,000), replacement with a Mitsubishi Hyper-Heat or Daikin Aurora often costs less out-of-pocket than the repair plus the next two repairs you will see. We give honest replace-or-repair analysis with the diagnostic.
Do you service Mitsubishi Hyper-Heat and Daikin Aurora cold-climate units?
Yes — heavily. We are factory-trained on Mitsubishi Diamond program and have completed Daikin Aurora technical certification. We stock common Mitsubishi parts (defrost sensors for MXZ-SM series, base pan heaters, communication boards) and Daikin parts (refrigerant solenoid valves, expansion valve actuators, communication PCBs). Bay Area cold-climate heat pump installs have grown 4x since 2022 driven by TECH Clean rebates, so this has become a core specialty.
Can a heat pump heat a Bay Area home below freezing?
Yes, with appropriate equipment. Mitsubishi MXZ-SM48NAMHZ rated for 100% heating capacity at 5°F handles even the coldest Portola Valley or Saratoga foothills nights. Daikin Aurora and Carrier Infinity Greenspeed similarly. Older non-cold-climate heat pumps (Goodman GSZ14, Rheem RP14) lose substantial capacity below 25°F and rely on backup electric heat strips. Bay Area design temp is 30-35°F so even non-cold-climate units work, just not efficiently below freezing.