HVAC Troubleshooting
AC Not Cooling?
Here’s What to Check First
Your air conditioner is running but the house isn’t getting cold. This is the most common summer call we get from Bay Area homeowners — and about 30% of the time, it’s something you can fix yourself in minutes.
No cool air at all?
If your AC won’t turn on at all, that’s a different problem — see our AC Won’t Turn On guide.
Common Causes
Six issues account for the vast majority of “AC running but not cooling” calls we respond to across the Bay Area.
1
Dirty Air Filter
The #1 cause and the easiest fix. A clogged filter restricts airflow across the evaporator coil, reducing cooling capacity by up to 15%. In severe cases, the coil freezes over completely. Check and replace your filter first — this solves the problem about 20% of the time.
2
Thermostat Set Incorrectly
More common than you’d think. Verify the thermostat is set to COOL (not HEAT or FAN ONLY), the temperature is set below current room temp, and the fan is set to AUTO (not ON). Someone may have changed it accidentally.
3
Dirty Condenser Coils
The outdoor unit rejects heat from your home. If the condenser coils are caked with dirt, dust, or leaves, heat can’t escape and cooling drops. You can carefully clean debris with a garden hose — spray from inside out, gentle pressure.
4
Low Refrigerant (Leak)
If your AC was cooling fine last week but gradually lost performance, you likely have a refrigerant leak. Signs: ice on the copper lines, hissing near the outdoor unit, system runs constantly but never satisfies. This requires a professional — refrigerant handling needs EPA 608 certification.
5
Frozen Evaporator Coil
If you see ice on the indoor unit’s copper lines or the coil itself, turn the AC off and run the fan only for 2–3 hours to thaw. A frozen coil is usually caused by low airflow (dirty filter) or low refrigerant. Running a frozen AC can damage the compressor.
6
Failed Capacitor or Contactor
The outdoor fan or compressor may have a failed start capacitor — the unit hums but doesn’t start, or the fan spins slowly. This is a common part failure, especially in Bay Area heat waves when the system runs hard. Requires a technician to replace.
Safe Checks You Can Perform
Work through these in order before calling a technician.
Check the air filter. Pull it out and hold it up to light. If you can’t see through it, replace it. This is the single most common fix.
Verify thermostat settings. Mode = COOL. Fan = AUTO. Set temp at least 3°F below current room temperature. Try fresh batteries if it’s battery-powered.
Check the outdoor unit. Is the fan spinning? Is the area around it clear? Remove any leaves, debris, or objects within 2 feet of the unit. Make sure nothing is blocking airflow.
Check the breaker. Look at your electrical panel. If the AC breaker has tripped, reset it once. If it trips again, do not reset again — call a technician.
Check all vents. Make sure supply vents are open and not blocked by furniture, curtains, or rugs. One or two closed vents won’t cause problems, but several will.
Look for ice. Check the copper lines going to the indoor unit. If there’s frost or ice, turn AC off, set fan to ON, and let it thaw for 2–3 hours before running cooling again.
Signs You Need a Professional
If your DIY checks didn’t solve it, these signs indicate a repair that requires a licensed technician.
Outdoor unit runs but fan doesn’t spin — likely a failed fan motor or capacitor. Don’t run the system without the fan — the compressor will overheat.
Ice on refrigerant lines after filter change — if ice returns after you’ve replaced the filter and thawed the coil, you likely have a refrigerant leak.
Breaker trips repeatedly — indicates an electrical fault (short circuit, ground fault, or failing compressor). Do not keep resetting.
System short-cycles — turns on for a few minutes, shuts off, repeats. Could be low refrigerant, oversized system, or a failing compressor. Stresses equipment and wastes energy.
Strange noises — grinding, squealing, or banging from the outdoor unit. Shut it off and call. These indicate mechanical failure that will get worse (and more expensive) if ignored.
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Frequently Asked Questions
The most common causes are a dirty air filter (restricts airflow), thermostat set incorrectly, dirty condenser coils (outdoor unit), or low refrigerant from a leak. Start by checking and replacing the filter — this fixes the problem about 20% of the time.
Common repairs: capacitor or contactor replacement ($150–$400), refrigerant recharge ($200–$600), fan motor ($300–$700). Major repairs like compressor replacement run $1,500–$3,000. We provide a diagnosis and upfront quote before any work. Learn more about AC repair.
General rule: if the system is under 10 years old and the repair is less than 50% of replacement cost, repair. If it’s 15+ years old or needs a major component like a compressor, replacement usually makes more financial sense — especially with current rebates on heat pumps. See our cost guide.
AC Still Not Cooling?
Same-day AC repair for Bay Area homeowners. We diagnose the problem, give you an upfront quote, and fix it — usually in one visit.
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