The short answer
An AC blows warm air because of a wrong thermostat setting, no power to the outdoor unit, a frozen indoor coil, low refrigerant, or a failing compressor or stuck reversing valve. In Vancouver, WA at 2026 prices, the first two checks are free, a frozen coil costs $80 to $400 to thaw and diagnose, a refrigerant leak $200 to $900 to find and fix, and a failed compressor $1,800 to $3,500.
In this guide
Check 1: The thermostat.
Estimated cost to fix: $0.
Check that:
- Thermostat is set to COOL, not HEAT or OFF
- Setpoint is below current room temperature (if the room is 78°F and the setpoint is 79°F, the AC is correctly doing nothing)
- Fan is set to AUTO, not ON (the ON setting blows air through the vents even when the AC is not running, which feels like warm air)
- Thermostat has power, batteries fresh, display working
- Someone in the house did not change the schedule without telling you
If the thermostat looks right and behaves right, move to check 2.
Check 2: The outdoor unit.
Estimated cost to fix: $0 if it is a tripped breaker or a pulled disconnect. A failed part means a service call.
If the thermostat is calling for cooling, the outdoor unit (the metal condenser box, usually on the side or back of the house) should be humming with its fan running.
If the outdoor unit is silent:
- Check the breaker in your main electrical panel. AC units have a dedicated double-pole breaker. If it tripped, flip it fully OFF, wait 30 seconds, flip it back ON. If it trips again immediately, stop and call us. That's an electrical fault.
- Check the outdoor disconnect. There's a small box mounted on the wall next to the outdoor unit. Open it: there should be a pull-out fuse or switch inside. Sometimes these get knocked out by landscaping or critters. Push it back in firmly.
- Check the condensate overflow switch. Modern AC systems have a safety switch that shuts down the system if the condensate drain backs up. The switch sits in the attic or utility closet, near the indoor coil. If the drain pan has water in it, the switch has tripped and the drain needs clearing, which is DIY-able but messy.
Check 3: The indoor coil (frozen).
Estimated cost to fix: $80 to $400 for a thaw + diagnostic. More if there's a cause to address.
Open the indoor air handler cabinet or furnace closet. Look at the indoor coil, the finned metal section where the refrigerant exchanges heat. If you see ice or frost:
- Turn the AC off at the thermostat. Set fan to ON (this helps thaw faster). Wait until the ice has fully melted before you turn cooling back on.
- Check the air filter. Restricted airflow, including a clogged filter, is the most common cause of a frozen coil. Replace a dirty filter.
- Check return registers for blockage. Furniture pushed against a return grille, closed registers, crushed flex duct, all reduce airflow and can freeze a coil.
- After thaw, restart and monitor. If the coil re-freezes within a day, the underlying cause is something else, usually low refrigerant. Call us.
Check 4: Low refrigerant.
Estimated cost to fix: $200 to $900, depending on leak complexity and refrigerant type.
If the AC runs but is not cooling well, and the coil is not frozen, the most common next cause is low refrigerant. You cannot check this yourself, it requires refrigerant gauges and is regulated by the EPA. (A side note for owners of older R-410A systems: in Washington, whole new systems installed after January 1, 2026 must use a lower-GWP refrigerant, and your system is still fine to service.) Symptoms that point to low refrigerant:
- Outdoor unit runs constantly without reaching thermostat setpoint
- Air from vents is cool but not cold
- Higher humidity inside even when AC is running
- Slight hissing or bubbling noise near the outdoor unit
- Ice on the copper refrigerant line outside
Refrigerant doesn't get "used up," so low refrigerant usually means a leak. A proper repair finds the leak, fixes it, and recharges. A contractor who just tops off the refrigerant without leak-testing is selling you a temporary fix. If your system uses R-22, U.S. production and import of that refrigerant ended on January 1, 2020, so a leak can only be refilled from recovered and reclaimed R-22 or stock made before 2020, and that often pushes the decision toward replacement.
Check 5: Failing compressor or reversing valve.
Estimated cost to fix a failed compressor: $1,800 to $3,500.
If none of the above check out, the issue is likely inside the outdoor unit itself. The compressor is the component that circulates refrigerant; when it fails, the system cannot move heat. On heat pumps, the reversing valve can also fail in a way that makes cooling impossible (stuck in heating mode).
Symptoms:
- Outdoor unit hums but doesn't actually cycle
- Repeated breaker trips on the AC circuit
- System blows warm air on both cooling AND heating modes (heat pump reversing valve)
At this stage, for older systems, replacement vs repair becomes a real conversation, see our repair-vs-replace guide for the rule of thumb, and what a new AC actually costs if replacing wins.
When to skip the self-checks and just call
If you smell something burning, see smoke, hear a loud grinding, or the breaker trips repeatedly, do not troubleshoot further. Shut the system off at the thermostat, and call us. Safety first; everything else can wait.
Getting help.
If checks 1 through 3 don't resolve your problem, you are almost certainly at a real service call. Schedule service and we will come out with the right tools to diagnose and quote the repair in writing before any work is done. Peak Care members get priority scheduling and 10% to 20% off parts and labor, depending on the plan.
Questions homeowners ask.
What's the first thing to check if my AC is blowing warm air?
Start with the thermostat, since a wrong setting costs $0 to fix. Verify it's set to COOL (not HEAT or OFF), that the setpoint is below the current room temperature, that the fan is set to AUTO rather than ON (ON blows air through the vents even when the AC isn't running, which feels like warm air), that the thermostat has power and fresh batteries, and that no one changed the schedule without telling you. If the thermostat looks and behaves correctly, move on to checking the outdoor unit.
What should I check if the outdoor AC unit is silent?
Check the breaker in your main electrical panel first, AC units have a dedicated double-pole breaker; if it tripped, flip it fully off, wait 30 seconds, then flip it back on (if it trips again immediately, that's an electrical fault, call a professional). Next check the outdoor disconnect box mounted on the wall next to the unit for a knocked-out pull-out fuse or switch. Finally check the condensate overflow switch near the indoor coil, if the drain pan has water in it, the safety switch has tripped and the drain needs clearing.
What does a frozen indoor AC coil mean, and how do you fix it?
If you open the air handler or furnace closet and see ice or frost on the indoor coil, turn the AC off at the thermostat and set the fan to ON to help it thaw, then wait until the ice has fully melted. Check the air filter, since restricted airflow, including a clogged filter, is the most common cause of a frozen coil, and replace it if needed. Also check return registers for blockages like furniture or crushed flex duct that reduce airflow. If the coil re-freezes within a day after thawing, the underlying cause is usually low refrigerant, and it's time to call a professional.
What are the signs of low refrigerant in an AC system, and can I fix it myself?
You cannot check refrigerant level yourself, it requires gauges and is EPA-regulated. Signs pointing to low refrigerant include the outdoor unit running constantly without reaching the thermostat setpoint, air from vents feeling cool but not cold, higher indoor humidity even with the AC running, a hissing or bubbling noise near the outdoor unit, and ice on the copper refrigerant line outside. Refrigerant doesn't get used up, so low refrigerant usually means a leak, and a proper repair finds and fixes the leak before recharging rather than just topping it off.
What does a failing AC compressor or reversing valve look like?
If the issue isn't the thermostat, outdoor power, a frozen coil, or low refrigerant, the problem is likely inside the outdoor unit itself. The compressor circulates refrigerant, and when it fails the system can't move heat; on heat pumps, a stuck reversing valve can also make cooling impossible by leaving the system in heating mode. Symptoms include the outdoor unit humming but not actually cycling, repeated breaker trips on the AC circuit, and the system blowing warm air on both cooling and heating modes. A failed compressor typically runs $1,800 to $3,500 to fix.
When should I stop troubleshooting my AC myself and call a professional?
If you smell something burning, see smoke, hear a loud grinding noise, or the breaker trips repeatedly, do not keep troubleshooting. Shut the system off at the thermostat and call a professional right away, safety comes first and everything else can wait. Also, if the thermostat and outdoor-unit checks (the two free, $0 fixes) don't resolve the problem, you're almost certainly at a real service call that needs proper diagnostic tools rather than more DIY steps.
Sources and resources
Reviewed for accuracy by Sam Tsarenko, founder of Pacific Peak Mechanical. This guide draws on the following primary sources:
- U.S. EPA, Section 608 Technician Certification, for refrigerant work requiring an EPA-certified technician
- ENERGY STAR, Maintenance Checklist, for annual check-ups, monthly filter checks, and dirty filters and coils shortening equipment life
- American Standard, Frozen Evaporator Coil? Don't Panic, Do This, for thawing with the fan on and poor airflow as the most common cause of a frozen coil
- U.S. EPA, Residential Air Conditioning and the Phaseout of HCFC-22, for the January 1, 2020 end of R-22 production and import
Related from Pacific Peak: AC repair in Vancouver WA · HVAC repair in Vancouver WA · AC installation in Vancouver WA
