⚡ Quick Answer
If your AC is running but not cooling, the most common causes are a dirty air filter, low refrigerant, frozen evaporator coils, or a failing compressor. Start by checking your filter and thermostat settings. Most issues in Cypress, TX homes can be diagnosed in under an hour by a licensed HVAC technician.
It’s one of the most frustrating things a Houston homeowner can experience: you hear your AC running, feel air coming through the vents, but the house just won’t cool down. In the middle of a Texas summer, this isn’t just uncomfortable — it can be dangerous.
At Mr. Cool AC & Heating, we’ve been helping Cypress and Greater Houston families stay cool since 1979. We see this exact situation dozens of times every spring and summer. The good news? In many cases, the fix is simpler than you think — and catching it early saves you money. Let’s walk through exactly what’s happening and what to do about it.
Most HVAC guides are written for dry, mild climates. Houston is different. Here’s why your AC is under more stress than almost anywhere else in the country:
The result: problems that would take years to develop in Denver or Dallas can surface in a single Houston summer. That’s why preventive maintenance isn’t optional here — it’s essential.
Before troubleshooting, confirm your system is truly ‘running.’ There’s an important difference between your AC blowing air and your AC actively cooling:
| What You See / Hear | What It Actually Means |
| Fan blowing, no cold air | Fan is on but compressor may be off |
| Outdoor unit not running | Compressor failure or thermostat issue |
| Air feels slightly cool but room stays warm | Low refrigerant or frozen coil |
| System clicks on but shuts off quickly | Short cycling — possible electrical issue |
| Water pooling near indoor unit | Frozen evaporator coil thawing |
Check your thermostat: is it set to ‘COOL’ and not just ‘FAN ON’? A thermostat accidentally set to ‘FAN’ will blow unconditioned air throughout your home indefinitely.
Here are the causes we diagnose most often in Cypress and Houston homes, ordered from most to least common:
This is the #1 cause we find — and the easiest to fix yourself. A clogged filter restricts airflow to the point where your system can’t move conditioned air through your home, even while running at full capacity.
DIY Fix: Turn off your system, locate your filter (usually in the return air vent or air handler), and replace it. In Houston, we recommend 1-inch filters rated MERV 8-11, changed every 30-60 days during peak season — not every 90 days as most packaging says.
| Pro Tip: Hold your old filter up to a light. If you can’t see light through it, it’s time for a new one — and your system has likely been struggling for weeks. |
Refrigerant is the substance your AC uses to absorb heat from your home’s air and release it outside. When refrigerant is low — usually because of a leak, not normal depletion — your system loses its ability to cool.
Symptoms of low refrigerant:
| Important: This is NOT a DIY repair. Refrigerant handling requires EPA 608 certification. If you add refrigerant without fixing the leak, you’ll be back in the same situation within weeks. A licensed tech needs to find and repair the leak first. |
Your evaporator coil (located in the indoor air handler) can freeze solid, completely blocking airflow. This sounds counterintuitive — ice forming on an AC unit — but it happens regularly in Houston, especially when airflow is restricted.
Common causes of a frozen coil:
DIY First Step: Turn the system OFF (not just ‘FAN’) and let the coil thaw for 24 hours. Change your filter. Then turn it back on. If it freezes again within 24-48 hours, call a technician — you likely have a refrigerant issue or airflow problem that needs professional diagnosis.
Your AC has two separate circuits: one for the indoor air handler (fan) and one for the outdoor compressor unit. If the compressor breaker trips, your fan will keep running but the outdoor unit shuts off — leaving you with airflow but no cooling.
DIY Check: Go to your electrical panel and look for tripped breakers (they’ll be in the middle position, not fully on or off). Reset once. If it trips again immediately, do not reset it again. A breaker that keeps tripping is protecting you from an electrical fault that needs professional attention.
The outdoor unit releases the heat your AC pulls from your home. When its coils are coated in dirt, debris, cottonwood, or grass clippings, it can’t release heat efficiently — and your cooling capacity drops significantly.
DIY Maintenance: Turn off power to the unit at the disconnect box. Gently rinse the coils with a garden hose (from the inside out, never a pressure washer). Clear away any vegetation within 2 feet of the unit. This should be done every spring before cooling season — ideally as part of a professional AC tune-up.
The compressor is the heart of your AC system — it pressurizes the refrigerant to drive the cooling cycle. When it fails, the system blows air but cannot cool at all. Compressor failure is the most expensive AC repair.
Signs of compressor problems:
| Cost Reality Check: Compressor replacement typically costs $1,500-$2,800 in the Houston area. If your system is 10+ years old, a full replacement may be more cost-effective. Ask about our financing options — we can often get you into a new, energy-efficient system for less than you’d expect per month. |
A malfunctioning thermostat can cause your AC to run without properly communicating with the compressor, resulting in airflow without cooling. This is more common with older analog thermostats, thermostats in direct sunlight, or those with dead batteries.
DIY Checks: Replace the batteries (even if the display is on). Verify it’s set to ‘COOL’ and the setpoint is at least 3-5 degrees below current room temperature. Make sure it’s not located near a window, lamp, or other heat source that could give it a false temperature reading.
Before you call a technician, run through this checklist. These are safe, effective steps that can solve the problem or give our team better information when you call.
Stop troubleshooting and call a professional HVAC technician immediately if:
| Situation | Risk Level | Why It’s Urgent |
| Breaker trips repeatedly | 🔴 High — Call Now | Electrical fault, fire risk |
| Ice on refrigerant lines | 🟠 Medium-High | System damage if ignored |
| Hissing/bubbling near outdoor unit | 🔴 High — Call Now | Refrigerant leak |
| Outdoor unit not running at all | 🟠 Medium-High | Compressor or capacitor |
| System short-cycles (on/off rapidly) | 🟡 Medium | Electrical or sizing issue |
| Home won’t cool below 80°F despite running | 🟡 Medium | Multiple possible causes |
| Burning smell from vents | 🔴 High — Call Now | Electrical fault, fire risk |
In Houston’s summer heat, a home that can’t cool below 80°F becomes dangerous for children, elderly family members, and pets within hours. Don’t wait to call. Mr. Cool offers same/next day service for urgent situations — call us at 281-859-7937.
Here’s a realistic look at what common repairs cost in the Greater Houston area. Keep in mind these are ranges — actual cost depends on your system’s brand, age, and the extent of the issue.
| Repair Type | Estimated Cost | DIY Possible? |
| Air filter replacement | $10-$30 | Yes |
| Thermostat replacement | $150-$400 | With skill |
| Capacitor replacement | $150-$350 | No — electrical risk |
| Refrigerant recharge + leak repair | $400-$1,200 | No — EPA licensed only |
| Evaporator coil cleaning (pro) | $200-$500 | Not recommended |
| Condenser coil cleaning (pro) | $100-$300 | Partially |
| Compressor replacement | $1,500-$2,800 | No |
| Full AC replacement (new system) | $4,000-$9,000+ | No |
Need help with the cost? Mr. Cool offers flexible financing options — because nobody should have to sweat through a Houston summer waiting to afford a repair.
The best AC repair is the one you never need. Here’s what our technicians recommend for Houston homeowners to avoid mid-summer cooling emergencies:
The most common reasons are low refrigerant, a dirty air filter restricting airflow, a frozen evaporator coil, or a failing compressor. Check your filter first and make sure your thermostat is set to ‘COOL’ — not just ‘FAN.’ If those are fine, call a licensed HVAC technician to check refrigerant levels and the compressor.
A properly functioning AC system should lower your home’s temperature by about 1-2 degrees per hour under normal conditions. In Houston’s extreme summer heat, a 3,000 sq ft home should reach your setpoint within 3-4 hours from a starting temperature of 82-85°F. If your system runs for 4+ hours without dropping the temperature, there is a problem that needs professional diagnosis.
No. Running your AC with a frozen evaporator coil can permanently damage the compressor — an expensive repair. Turn the system off completely (not just ‘FAN’) and let the coil thaw for 24 hours. Change your air filter. If it freezes again, call a technician — you likely have a refrigerant leak or serious airflow restriction.
Cost depends on the cause. A dirty filter replacement is $10-$30 and is DIY. Refrigerant leak repair and recharge runs $400-$1,200. Compressor replacement is $1,500-$2,800. A full system replacement ranges from $4,000-$9,000+. Mr. Cool provides free estimates and offers financing options so cost doesn’t force you to delay a necessary repair.
First: check the thermostat setting, replace the filter, and check your circuit breaker. Second: check whether the outdoor unit is running. If the outdoor unit is off or making unusual sounds, call a licensed HVAC technician immediately. In extreme heat (95°F+), an inoperative AC can make your home unsafe within a few hours. Mr. Cool AC & Heating offers same/next day emergency service at 281-859-7937.
Is Your AC Running But Not Cooling?
Mr. Cool AC & Heating has been diagnosing and fixing Houston HVAC systems since 1979.
Family-owned. Licensed (TACLB24041E). Honest pricing. Same/Next Day Service.
Call: 281-859-7937
Email: mrcoolair@gmail.com • mrcoolair.com First-time service call: $49.99 (conditions apply)
