Valderrama HVAC
Call

AC Running But Not Cooling? 11 Causes & Fixes (2026)

The system hums, air comes out of the vents — but the house keeps getting warmer. It is the single most common AC complaint in Texas, and the fix ranges from a $10 filter to a $2,800 compressor. Work through the free checks first, then the causes ranked by how often we actually see them.

4 things to check before you call anyone

  1. 1

    Check the thermostat

    Set to COOL, fan on AUTO, temperature at least 3–5°F below the current room reading. Replace the batteries while you are there — a weak thermostat battery causes a surprising number of “dead AC” calls.

  2. 2

    Check the air filter

    A completely clogged filter can choke airflow enough that the coil freezes and cooling stops. If you cannot see light through it, replace it. In Texas summer, filters need changing every 30–60 days.

  3. 3

    Check the breaker panel

    The outdoor condenser and indoor air handler are usually on separate breakers — the indoor fan can run (blowing warm air) while the outdoor unit has no power. Flip any tripped breaker fully OFF, then ON. If it trips again, stop and call a pro.

  4. 4

    Check the outdoor unit

    Is the condenser fan spinning? Is the unit buried in grass clippings, leaves or cottonwood fluff? Clear 2 feet of space around it and gently rinse the coil fins with a garden hose (power off first, never a pressure washer).

If none of those restored cooling, the problem is inside the system. Here are the causes in rough order of frequency, with 2026 Texas repair costs.

The 11 causes, ranked by frequency

  1. 1

    Dirty air filter

    The #1 cause and the only one that costs $10 to fix. Restricted airflow means less air over the coil, less cooling, and eventually a frozen coil. Replace and retest in an hour.

  2. 2

    Thermostat problems

    Wrong settings, dead batteries, or a miscalibrated sensor reading the wrong temperature. Smart thermostats also lose their C-wire power — if the screen is dim or blank, that is your clue.

  3. 3

    Dirty condenser coils

    The outdoor coil dumps your house’s heat outside. When it is caked with grime, the system runs constantly and barely cools. A garden-hose rinse helps; a proper coil cleaning is $100–$250.

  4. 4

    Low refrigerant (a leak, not “usage”)

    Refrigerant is not consumed like gas in a car — if it is low, there is a leak. Symptoms: warm air, hissing, ice on the copper lines. Recharge runs $200–$650; leak repair adds $200–$1,000 depending on location.

  5. 5

    Frozen evaporator coil

    Caused by #1 or #4 above. The ice blocks airflow entirely. Turn cooling OFF, run the fan to thaw (2–4 hours), fix the root cause. Do not chip the ice off.

  6. 6

    Failed capacitor or contactor

    The parts that start and power the compressor and fan. Texas heat kills them faster than anywhere — this is the most common professional repair we see at $150–$400.

  7. 7

    Leaky ductwork

    The AC may be cooling fine — into your attic. Duct leaks waste 20–30% of cooled air in the average Texas home. Sealing runs $300–$800 and often pays for itself in one summer.

  8. 8

    Faulty compressor

    The heart of the system. If it hums and clicks but never starts (and the capacitor is fine), you are looking at $1,500–$2,800 — on an older unit, that is replacement territory.

  9. 9

    Blocked or closed vents

    Closed supply vents do not “save energy” — they raise duct pressure, reduce total airflow, and can freeze the coil. Open at least 80% of vents and keep furniture off them.

  10. 10

    Undersized or aging system

    If the AC could never keep up on 100°F days, it may simply be undersized for the house — or worn out. Systems over 12–15 years old lose capacity steadily. At that point, compare <a href="/cost/hvac-replacement-cost/">replacement costs</a>.

  11. 11

    Blower fan problems

    A weak or dead blower motor means little air reaches the rooms even though the system runs. Motor replacement is $400–$800; sometimes it is just a $150 capacitor.

Call a pro immediately if…

you hear hissing near the refrigerant lines, see ice on the copper lines or air handler, smell anything burning, or the breaker trips a second time. Those four symptoms mean “turn it off now” — running the system further can turn a mid-size repair into a dead compressor. For nights and weekends: 24/7 emergency AC repair.

What the fix costs (Texas, 2026)

ServiceTypical cost (2026)Notes
Air filter replacement$10 – $40DIY
Condenser coil cleaning$100 – $250Pro recommended
Capacitor / contactor$150 – $400Most common pro repair
Refrigerant recharge$200 – $650Plus leak repair if needed
Duct sealing$300 – $800Pays back via energy bills
Blower motor$400 – $800Parts + labor
Compressor$1,500 – $2,800Consider replacement instead

Full price breakdown by repair type and city: AC repair cost guide. Ready for a diagnosis? Top AC repair companies in Texas or AC repair in Houston.

Still not cooling? Get a diagnostic from a licensed pro

Most Texas companies charge $75–$150 for the visit and waive it if you approve the repair.

Call (713) 555-0100 Get Free Quotes

Who fixes this in Houston

TDLR-licensed companies from our directory that list this service. Ratings shown are Google ratings, as text.

All Houston AC repair companies →

Frequently asked questions

Why is my AC blowing warm air instead of cold?

Most often: the outdoor unit lost power (tripped breaker), a failed capacitor, or low refrigerant. Check the filter and breaker first — if those are fine, you need a diagnostic.

Can I just add refrigerant myself?

No. Refrigerant handling requires EPA 608 certification, and “topping off” without finding the leak wastes money and harms the environment. Low refrigerant always means a leak.

How long should I wait after changing the filter?

If the coil was frozen, turn cooling off and run the fan for 2–4 hours to thaw, then restart. If cooling does not recover within a few hours, the filter was not the (only) problem.

Is it worth repairing a 15-year-old AC that is not cooling?

Only for cheap fixes (capacitor, contactor, cleaning). Any repair over $1,000 on a 15-year-old system — especially one using R-22 refrigerant — usually loses to replacement on pure math.

Get free diagnostic quotes

Tell us what you need and we will match you with licensed HVAC contractors that service your ZIP code. Free, fast, no obligation.

Free service. We may earn a referral fee from the companies we connect you with — it never changes your price.