What's it doing?
Ordered by how often each cause turns out to be the answer across our five metros.
Running, but the air isn't cold
the most common call
Likely causes, most common first
- Dirty filter. Restricts airflow; the evaporator coil can't absorb heat and eventually freezes. In Houston and Miami humidity this happens faster.
- Thermostat. Set to FAN not COOL, or a wiring fault so the condenser never gets the call.
- Low refrigerant. Systems don't consume it — low means a leak. Recharge without repair is temporary and R-410A is expensive now.
- Dirty condenser coil. Phoenix dust and LA cottonwood pack fins solid; the unit can't reject heat.
- Failed run capacitor. Hums, doesn't start. Heat kills capacitors — Phoenix rooftop units go through them fastest.
- Compressor. Least common, most expensive. Diagnosed by amp draw and pressures.
Check before you call
- Thermostat on COOL, setpoint 3°F under room temp.
- Filter: if it's gray, replace it.
- Outdoor fan spinning? Coil packed with debris? Clear two feet around it.
- Ice on the lines? Shut it off, FAN only two hours, then call — a frozen coil hides the real fault.
What the tech checks
- Temperature split across the coil (15–20°F healthy).
- Static pressure and airflow before blaming refrigerant.
- Superheat/subcooling — the real charge test.
- Capacitor µF against rating; >10% low is replace.
Won't turn on at all
no fan, no hum
Likely causes, most common first
- Tripped breaker or blown disconnect fuse. Reset once. Trips again → a short. Stop.
- Thermostat power. Dead batteries or a blown 3-amp fuse on the air handler board.
- Condensate float switch. Pan full, switch cuts power. Very common in humid metros.
- Contactor. Pitted or welded contacts.
- Control board. No 24V call being sent.
Check before you call
- Both breakers — outdoor unit and air handler. Reset once only.
- Thermostat screen blank? Batteries first.
- Standing water in the pan → clear the drain line.
- Outdoor disconnect pull-out seated?
What the tech checks
- 24V at thermostat, air handler, contactor coil.
- Contactor contacts and coil.
- Board fuse and outputs.
- Drain line and float switch.
Cooling, but weakly
runs all day, never catches up
Likely causes, most common first
- Airflow. Filter, closed registers, collapsed flex duct, slow blower.
- Dirty evaporator coil. Years of bypass dust.
- Marginal charge. Slightly low, not empty.
- Duct leakage. 20–30% loss is normal in older Dallas and LA homes with attic ducts.
- Aging system. A 15-year-old unit delivers 70–80% of nameplate.
Check before you call
- Filter, again.
- Every supply open, every return clear.
- Feel attic ducts for cold air at joints.
- Register-to-return temperature difference under 12°F means a real problem.
What the tech checks
- Static pressure — the best duct/blower indicator.
- Evaporator coil inspection.
- Charge by superheat/subcooling.
- Duct leakage assessment.
Leaking water inside
puddle under the air handler
Likely causes, most common first
- Clogged condensate line. Algae. The large majority of indoor leaks, especially Houston and Miami.
- Cracked or rusted pan.
- Frozen coil thawing. Overwhelms the drain.
- Mis-sloped or disconnected drain.
- Failed condensate pump.
Check before you call
- Shut the system off — water damage compounds.
- Find the PVC drain stub outside; a wet/dry vac on it clears most clogs.
- Ice on the coil? It's airflow or charge wearing a leak costume.
- Pump running? Float stuck?
What the tech checks
- Drain clearing and flow verification.
- Pan, slope, float switch.
- Underlying airflow/charge fault if ice was involved.
- Pump and check valve.
A noise it didn't make before
identify it by the sound
Likely causes, most common first
- Buzzing, fan not turning. Capacitor.
- Repeated clicking. Contactor chatter or a board relay.
- Grinding or screeching. Motor bearings. Stop running it.
- Hissing or bubbling. Refrigerant escaping.
- Banging on startup. Loose panel, debris in the fan, failing compressor mount.
- Hum, click, repeat. Compressor tripping its overload.
Check before you call
- Locate it: indoor, outdoor, or ducts.
- Buzzing outdoor unit with a still fan — shut it off. Don't push the fan.
- Rattling — check panels and screws first.
- Grinding — off, now.
What the tech checks
- Capacitor, motor amps, bearing play.
- Contactor and relays under load.
- Electronic leak detection.
- Compressor start characteristics.
Freezing up
ice on the lines or coil
Likely causes, most common first
- Restricted airflow. Filter, coil, blower.
- Low refrigerant. Lower pressure, colder coil.
- Running cool mode in cold weather. Below ~60°F outdoors most systems ice without a low-ambient kit. Rare in these five metros; happens in LA winters.
- Stuck contactor. Outdoor unit never stops.
- Failed blower. Coil freezes solid within the hour.
Check before you call
- Cooling off, FAN ONLY, 2–4 hours to thaw. Running it frozen slugs the compressor.
- Replace the filter while it thaws.
- Ices again within an hour with a clean filter → charge or blower. Call.
- Don't chip ice off the fins.
What the tech checks
- Airflow first — static, blower, coil.
- Then charge on a fully thawed system.
- Contactor for welded contacts.
- Leak search if charge is low.
- Return air78°Fwarm, humid room air pulled back to the unit
- FilterMERV 8–11a packed filter starves everything downstream of airflow
- Evaporator coil≈40°Frefrigerant boils inside and absorbs heat; water drips to the pan and drain
- Blower350–400 CFM/tonpulls the air across the coil and pushes it into the ducts
- Supply air58–62°F15–20°F colder than the return when the system is healthy
When should you stop and call right now?
- Burning or electrical smell from a vent or the outdoor unit
- The breaker trips again right after reset
- Buzzing or arcing at the disconnect or contactor
- Ice on the lines while running
- Indoor temperature climbing on a heat-advisory day
- Water spreading beyond the pan toward walls or floor
Should you repair or replace the air conditioner?
A 15-year-old 10 SEER unit delivers maybe 8 SEER. A current 15 SEER2 unit uses roughly 40–45% less electricity for the same cooling. On a $250/month Phoenix or Houston summer bill that's $100+/month back. Put that against the repair quote and the replacement quote. Also: equipment since 2025 uses R-454B or R-32, not R-410A — a replacement now is on the current refrigerant. Full decision on the installation page.
Before the air conditioning technician arrives
- Thermostat on COOL, set 3°F below room temperature, fresh batteries if it is blank
- Filter checked — a gray filter is the cause of half the weak-cooling service calls
- Ice on the lines: cooling OFF, FAN only, so the AC can be diagnosed when the technician arrives
- Emergency or not: a burning smell, a breaker that re-trips or water past the pan is an emergency service call; weak cooling can wait for the next slot
- What it costs: ask for the diagnostic price on the phone and whether it is credited to the repair
AC repair questions, answered
Is emergency AC repair available 24 hours a day?
Yes. Urgent HVAC Service is answered around the clock and routes to air conditioning contractors who run after-hours service in all five metros. Overnight visits usually carry an emergency premium on the diagnostic, which the contractor states before coming out.
How much does an AC repair cost?
The diagnostic runs about $75–$180 and is usually credited toward the repair. A capacitor or contactor is $140–$420, a refrigerant leak repair $400–$1,700, a compressor $1,400–$3,000 and up. The contractor sets the price after seeing the unit; the ranges on this page exist so you can tell a fair quote from a bad one.
Why is my air conditioner running but not cooling?
Airflow or charge, in that order. A packed filter or dirty coil starves the system and the coil freezes; a refrigerant leak lowers the pressure and does the same. Check the filter and the outdoor coil first; if there is ice on the lines, shut it off and run the fan for two hours before anyone can diagnose it.
Should I keep resetting a breaker that trips?
No. Reset it once. If it trips again there is a short, a seized compressor, or a failing motor, and each reset does damage. Leave it off and call.
What does an AC service call include?
The technician measures the temperature split across the coil, static pressure and airflow, the refrigerant charge by superheat and subcooling, and the capacitor against its rating — then quotes the repair. Anyone who quotes a compressor without those numbers is guessing.
Do I need a permit for an AC repair?
Not for a repair. Replacing the condenser, coil or air handler usually does need a mechanical permit; Phoenix exempts a like-for-like replacement. Each metro page names the permit office.
How fast can an air conditioning technician get to me?
Same-day in most cases, and often within hours for a system that is down during a heat advisory. During the July peak, slots fill by noon, so the earlier you call the better.
What should I do while I wait for the technician?
Set the thermostat to OFF, or FAN ONLY if there is ice on the lines. Replace a gray filter. Clear two feet around the outdoor unit. If water is spreading past the drain pan, keep the system off until the technician arrives.
AC repair by metro
Each city page covers local climate, permits, utility rebates and the failure modes specific to that market. Every metro page covers emergency air conditioning service, same-day AC repair, HVAC technician licensing, and the repair cost you should expect from a licensed service call.
References: EPA — HFC phasedown and the refrigerant transition · US Department of Energy · Carrier residential · Trane residential
Ask before you call
Not sure what's wrong, or whether it's urgent? Describe it. Questions that come up often get added to this page.