Few household problems are as immediately miserable as an air conditioner that gives up during an Iowa heat wave. The system hums along, air moves through the vents, and yet the house climbs past comfortable by the hour. The causes range from a thirty-second fix to a major component failure, and you cannot tell which from the symptom alone. But you can narrow the field before you call, which makes the repair conversation faster and often cheaper.

Start with the genuinely simple causes

Before assuming the worst, check the short list of things that homeowners can safely verify:

  • Thermostat settings: confirm it is set to cool, the setpoint is below room temperature, and the fan is on auto. If the display is blank, try fresh batteries.
  • Air filter: a filter clogged solid can restrict airflow so severely that cooling collapses. If you cannot remember the last change, that is your first move.
  • Breaker and disconnect: check whether the outdoor unit's breaker has tripped. A single trip can happen; repeated trips mean stop resetting and call.
  • Vents and returns: make sure supply vents are open and return grilles are not blocked by furniture.
  • Outdoor unit: clear away grass clippings, leaves, and cottonwood matting on the condenser. Des Moines summers coat outdoor units fast.

If those checks restore normal cooling, you are done. If not, the cause is internal and the next step is professional diagnosis.

The causes that need a professional

Dirty coils beyond the surface

The outdoor condenser coil and the indoor evaporator coil both have to move heat to cool your home. When they are coated in grime, the system runs longer and cools less. Surface debris you can rinse away gently is one thing; deep coil cleaning is a maintenance visit. Our AC cleaning page explains what that covers.

Refrigerant problems

Refrigerant is the working fluid of air conditioning, and it does not get used up. If the level is low, there is a leak. Signs can include gradually weakening cooling, ice on the refrigerant lines or indoor coil, and hissing sounds. Refrigerant work is federally regulated and strictly professional territory: no homeowner should be handling it, and any contractor who offers to "top it off" without finding the leak is offering a temporary bill, not a fix.

Compressor trouble

The compressor is the heart of the system, and when it struggles or fails, cooling stops. Hard starting, clicking at the outdoor unit, warm air with a running fan, or a unit that will not start at all can all point here. Compressor repairs are among the most significant in residential cooling, which is where the repair vs. replacement conversation often begins.

Capacitors and contactors

These small electrical components start and run the motors. They fail commonly, especially during heat waves when systems work hardest, and the symptom is often an outdoor unit that hums but will not spin or start. The parts are modest; the diagnosis still belongs to a professional because the inside of that cabinet holds lethal voltage even with the power off.

Frozen evaporator coil

Ice on the indoor coil or the refrigerant line is a symptom, not a cause. It usually traces to restricted airflow (that filter again) or low refrigerant. Turn the system off and let it thaw completely before any contractor visit; running a frozen system can damage the compressor.

Ductwork problems

Sometimes the equipment is fine and the delivery system is not. Disconnected, crushed, or leaky ducts, especially in attics and crawl spaces, can dump cooled air where nobody lives. If some rooms cool and others never do, ducts belong on the suspect list.

When "not cooling" is an emergency

During a genuine heat advisory, a dead AC is more than uncomfortable for infants, elderly family members, and anyone with health conditions. If vulnerable people are in the home, treat it as urgent: move them to a safe temperature and read our emergency HVAC guidance on confirming real-time contractor availability.

What to tell the contractor

You do not need a theory. You need observations: what the system is doing, when it started, whether it is constant or comes and goes, what you already checked, and anything unusual you have seen, heard, or smelled. Those details, plus your address and the system's approximate age, are everything a contractor needs to arrive prepared. If you are in the Des Moines area, call (515) 724-6446 to connect with an independent local contractor, and verify licensing and insurance before authorizing any work.