Why Is My AC Not Cooling?
7 Causes - Lewisville TX Homeowner's Guide

Quick Answer: 7 Reasons Your AC Isn't Cooling

1. Dirty air filter - restricted airflow across the indoor coil
2. Frozen evaporator coil - low refrigerant or airflow restriction
3. Low refrigerant / refrigerant leak - requires EPA-certified technician
4. Failed capacitor - the most common summer call we run
5. Dirty condenser unit - debris on the outdoor coil
6. Thermostat issue - settings, wiring, or dead batteries
7. Compressor failure - the worst-case repair

Cause #1: Dirty Air Filter

A clogged filter restricts airflow across the indoor evaporator coil, which causes warm air at the supply registers and (if left long enough) leads to a frozen coil. North Texas dust and cottonwood season can clog a filter in 30 days.

DIY check (4 steps):

1. Locate your air handler filter (return air grille or air-handler cabinet)
2. Pull the filter and hold it up to a light. If you cannot see daylight through it, replace it
3. Match the size on the filter frame and replace with a same-size MERV 8-11 filter
4. Run the system for 15 minutes and check the supply register

Cause #2: Frozen Evaporator Coil

Visible ice on the refrigerant line or indoor evaporator coil. Caused by restricted airflow (often dirty filter) or low refrigerant charge. The system needs to thaw before it will cool again.

DIY check: Shut the system off at the thermostat (do not just raise the setpoint). Switch the thermostat fan to ON and let the blower run 1-2 hours to thaw the coil. Once thawed, replace the filter if it is dirty. If the coil freezes again within hours, the cause is low refrigerant, not airflow - call a technician.

Cause #3: Low Refrigerant or Refrigerant Leak

Refrigerant does not get consumed - the system is a closed loop. If you are low on refrigerant, you have a leak. Symptoms: warm supply air, ice on the refrigerant line, system that needs frequent "recharging."

Call a pro: Refrigerant handling requires EPA Section 608 certification. Adding refrigerant without finding the leak is throwing money at a hole. Our diagnostic uses electronic leak detector and dye to locate the leak, then we repair, evacuate, and recharge to manufacturer spec.

Cause #4: Failed Capacitor

The most common summer service call we run. The dual-run capacitor stores the boost charge that starts the compressor and condenser fan motor. Heat fatigue from North Texas summers kills capacitors well before their label rating.

Symptoms: outdoor unit humming with no fan spin, or system that runs briefly and shuts off. Capacitor replacement is a fast same-day repair - parts on every truck.

Call a pro: Capacitors store high-voltage charge even when power is off. Do not open the condenser unit.

Cause #5: Dirty or Blocked Condenser Unit

The outdoor condenser releases heat extracted from your home. If grass clippings, cottonwood fluff, or debris cover the coil fins, the system cannot release heat efficiently and cooling drops.

DIY check (safe steps):

1. Shut power off at the outdoor disconnect (the box mounted on the wall next to the condenser)
2. Clear leaves, grass, and debris from around the unit (2 feet of clearance recommended)
3. From outside the unit, gently spray the coil fins with a garden hose at low pressure - top down
4. Let it dry for 30 minutes, restore power, run the system

Do not pressure-wash the fins (they bend) and do not open the cabinet.

Cause #6: Thermostat Settings or Wiring

Sometimes the AC isn't cooling because the thermostat isn't telling it to.

DIY checks (5 quick):

1. Confirm the thermostat is set to COOL (not OFF, not HEAT, not FAN-only)
2. Confirm the setpoint is below the current room temperature
3. Replace thermostat batteries if it has them
4. Check the thermostat display - if it is blank, the wiring or batteries need attention
5. If a smart thermostat shows a wiring error or low-voltage warning, that points to an air-handler or condensate-overflow trip

Cause #7: Compressor Failure

The worst-case repair. The compressor is the most expensive single component in an AC system. On a system over 10 years old with a failed compressor, replacement of the entire outdoor unit is usually a better economic call than a compressor swap.

Symptoms: outdoor unit clicks on but the compressor won't run, breaker trips immediately on AC call, or system runs but no cooling at all (fan still spinning).

Call a pro: we diagnose with amp clamp and ohmmeter and discuss repair-vs-replace economics at that point.

When AC Issues Become an Emergency in Texas Summer

If indoor temperature is climbing over 85F with vulnerable household members, infants, or pets - that is an emergency. Call our office (817-725-9234) during business hours for same-day dispatch, or see our emergency AC repair page for the dispatch process and what counts as an emergency.

When to Call Graco vs. DIY

• DIY safe: air filter replacement, thermostat battery check, condenser coil rinse (power off), thermostat setting verification
• Call a pro: refrigerant work, capacitor replacement, compressor diagnostic, electrical concerns, recurring freeze-ups, breaker trips, anything involving the sealed refrigerant system

FAQs

Schedule AC Repair in Lewisville or Call 817-725-9234

Most "AC not cooling" calls are same-day fixes during business hours. Call 817-725-9234 or see AC repair details.

Related reading: AC making a loud noise? What each sound means and AC repair cost in Lewisville.