AC Troubleshooting
Why is my AC not cooling?
The quick checks that get most Des Moines air conditioners cooling again, what a technician looks at next — and why a house that won’t cool in an Iowa heat wave shouldn’t wait.
When a Des Moines AC runs but won’t cool during a humid Iowa heat wave, the cause is usually something basic: the thermostat is on the wrong setting, the outdoor unit lost power at the breaker, or a clogged filter is choking airflow. If those check out, the trouble is often a frozen coil or low refrigerant — and low refrigerant always means a leak to repair, never a system that simply ran out. Running a struggling AC in the heat only stresses it further, so it pays to track the problem down quickly.
Start with these quick checks
- 1 Set the thermostat to COOL and AUTO, a few degrees below the room. On HEAT, on FAN/ON, or with the setpoint above the current temperature, the system never actually calls for cooling. Swap dead batteries while you are there.
- 2 Check both breakers. The indoor air handler and the outdoor condenser are often on separate breakers. A tripped outdoor breaker leaves the indoor fan moving air that was never cooled.
- 3 Replace a dirty air filter. A clogged filter chokes airflow, which weakens cooling and can freeze the indoor coil. Less air across the coil means less cold air at your vents.
- 4 Clear the outdoor unit. Pull weeds, grass clippings, leaves, and cottonwood fluff away from the condenser, keep about two feet of clearance, and rinse a visibly dirty coil with a gentle hose.
- 5 Open and unblock vents and returns. Closed supply registers and furniture over return grilles starve the system of airflow, so rooms never reach the setpoint.
- 6 Look for ice on the coil or refrigerant lines. Frost means the system is freezing up. Turn it off and let it fully thaw before running it again, or you risk damaging the compressor.
Getting warm air specifically — not just weak cooling? Walk through why is my AC blowing warm air . Seeing frost or ice on the unit? Start with why is my AC freezing up before running it again.
What a technician checks next
If the basics look right and the house still won’t cool, the cause is usually inside the equipment. These checks take tools and training:
- Refrigerant charge and leak search. A low charge always means a leak to find and seal, not refrigerant that simply ran out. Cooling fades as the charge drops.
- Capacitor and contactor. A common reason the outdoor unit hums or sits silent while the indoor blower keeps running and the house never cools.
- Compressor and condenser fan motor. If the compressor or its fan is not running, the system cannot move heat out of your home no matter how long it runs.
- Dirty coils and metering device. A caked condenser coil or a failing expansion valve keeps the system from rejecting heat and cooling properly.
- Airflow and duct problems. Leaky, undersized, or crushed ducts and a weak blower can leave a healthy AC unable to keep up on the hottest days.
Tip: if the thermostat is blank or won’t respond at all, the AC may be fine — the control is the problem. See why isn’t my thermostat working . A yearly cooling tune-up catches the dirty coils and low-charge issues that cause weak cooling; here’s what’s in an HVAC tune-up .
Iowa myth vs. truth
Myth: “When it’s 95° out, it’s normal for the AC to barely keep up.”
A healthy, properly sized system should hold your setpoint even in a Des Moines heat wave. Cooling that steadily falls behind usually points to low refrigerant, restricted airflow, or dirty coils — not just the weather. If the system is genuinely undersized for the home, our what size HVAC do I need guide explains how sizing is done right.
Emergency service
Still no cooling in your Des Moines home?
In a IA heat wave, a house that won’t cool is more than uncomfortable — it can be dangerous for infants, older adults, and pets. All Seasons HVAC offers emergency HVAC service across the Des Moines metro — with no extra charge for emergencies.
Common questions
Why is my AC running but not cooling the house?
The blower can run while real cooling has stopped. Usual causes are the outdoor unit losing power, a clogged filter, a frozen coil, low refrigerant from a leak, a failed capacitor or compressor, or airflow problems in the ducts. Start with the thermostat, breakers, and filter, then have the rest diagnosed.
Why is my AC not turning on at all?
Check the thermostat mode, setpoint, and batteries first, then the breakers for both the indoor and outdoor units. Many systems also have a float switch that cuts power when the condensate drain backs up. If those look right and it still will not start, it usually needs a technician.
Can a dirty filter keep my AC from cooling?
Yes. A clogged filter restricts airflow, which reduces cooling and can freeze the indoor coil. A frozen coil blocks airflow even more, so the air at your vents feels weak or warm. Changing the filter is the first thing to check.
Is it an emergency if my AC stops cooling in a heat wave?
It can be. In an Iowa heat wave a house that will not cool is dangerous for infants, older adults, and pets. All Seasons HVAC offers emergency HVAC service at (515) 417-0296 when the cooling quits at the worst time.