01Set to Cool, Set Below Room Temp

Sounds basic. It's also the #1 reason "why is my AC not cooling" calls turn out to be a five-second fix. Confirm three things:

• Mode is set to COOL, not FAN or OFF.
• Set temperature is at least 3°F below current room temp.
• Fan is on AUTO, not ON (ON-mode blows uncooled air between cycles, fooling you into thinking the AC failed).
• Batteries aren't dead — most thermostats blink or show a low-battery icon.

If the thermostat screen is blank, replace the batteries first. If still blank, the 24V transformer or low-voltage wiring is likely the issue — that's a pro call.

02The $20 Fix That Solves 30% of Calls

A dirty filter chokes airflow across the evaporator coil. The system runs but moves almost no air — and worse, the coil eventually freezes solid (see Fix 3). DFW dust and pollen clog filters faster than the rest of the country.

• Replace 1" filters every 30–60 days in cooling season.
• Replace 4"–5" media filters every 6 months.
• Match the MERV rating to your system — MERV 8–11 is the sweet spot for most DFW homes. MERV 13+ on an undersized blower can starve the system for air.

03Frozen Evaporator = Stop the System Now

If you see ice on the copper refrigerant lines, frost on the air handler, or water dripping from the indoor unit, your evaporator coil is frozen. Causes: dirty filter, blocked return air, low refrigerant, or a failing blower motor.

• Turn the system OFF at the thermostat and run the fan only for 1–3 hours to thaw.
• Replace the filter while you wait.
• Once thawed, restart in COOL. If it freezes again within an hour, you have low refrigerant or a deeper airflow problem — call a pro.

04Clear the Coils, Hear the Fan

Walk outside to your condenser unit. It should be humming and the fan on top should be spinning fast. Check for:

• Debris in the fins — grass clippings, leaves, cottonwood fluff. Spray it down with a garden hose (not a pressure washer — fins bend easily).
• Bent fins from hail or weed trimmers — straighten with a fin comb.
• Silent fan while the system is calling for cooling — usually a failed capacitor (Fix 7).
• Loud humming + no fan spin — definitively a capacitor.

05Two Breakers, One Disconnect

Your AC has two breakers — one for the air handler/furnace (indoor) and one for the condenser (outdoor) — plus a pull-disconnect box on the wall beside the outdoor unit. Check all three:

• If a breaker is tripped, flip it fully OFF, then ON.
• If it trips again immediately — stop. You have a short or a seized component. Call a pro.
• If the pull-disconnect is pulled out (some look like a fuse handle), reseat it firmly.

06If Air Blows But Doesn't Get Cold

Low refrigerant always means there's a leak — refrigerant is a closed loop, it doesn't get "used up." A pro will find the leak, repair it, pull a deep vacuum on the system, and recharge to manufacturer spec. Per EPA Section 608, only certified technicians can legally handle refrigerant.

Warning sign: the indoor coil ices over even with a clean filter, electric bills suddenly spike, or the lineset feels colder than usual near the condenser.

07The #1 Summer Failure in DFW

Capacitors are batteries that give the compressor and fan motors a starting jolt. Texas heat kills them — they bulge, leak, or fail outright. Symptoms:

• Outdoor unit hums but the fan doesn't spin.
• System clicks on, then clicks off after 5–10 seconds.
• You can spin the outdoor fan with a stick and it then runs (a "kickstart" test — replacement needed).

A capacitor swap is fast and inexpensive ($150–$350 installed). A failed contactor (the relay that powers the condenser) is also common and just as fast.

08The Float Switch That Shuts You Down

Modern AC systems include a safety float switch on the condensate drain. If algae or sludge blocks the drain line, water backs up and the switch shuts the system off to prevent ceiling damage. Symptoms:

• System runs the fan only, never the compressor.
• Water around the indoor unit or in the secondary drain pan.
• Drain line outside the home doesn't drip during operation.

DIY flush: pour 1 cup of distilled white vinegar into the drain cleanout pipe (usually a vertical PVC pipe near the air handler) every 60 days. Persistent backups need a pro to vacuum-clear the line.

09The Cool Air Never Reaches You

If the air at the supply registers is cold but rooms still feel hot, the issue is ductwork, not the unit. Studies by the U.S. Department of Energy show typical residential ductwork loses 20–30% of conditioned air to leaks. In DFW, where ducts often run through unconditioned attics, that loss can hit 40%.

• Check the attic for disconnected duct boots or crushed flex duct.
• Feel along visible duct seams for cool air escaping.
• A blower-door + duct-leakage test from an HVAC pro is the gold standard.

10Replacement Territory

The compressor is the heart of your AC. When it fails, the system blows ambient-temperature air no matter what you do. Symptoms:

• Outdoor unit is silent or makes a loud groaning/grinding sound.
• Hard-start clicks but doesn't turn over.
• Breaker trips immediately when the compressor tries to engage.

On a system 10+ years old, compressor failure usually means it's time for a full replacement — see our AC Installation Grand Prairie TX guide for what to expect.