Why Is My AC Not Blowing Cold Air? 9 Causes Texas Homeowners See Most
The blower is running, air is moving, and none of it is cold. Here is how a technician narrows that down, in the order they actually check.
Texas furnaces sit idle for eight or nine months and then get asked to perform on the first genuinely cold night. That is when problems surface, usually all across the neighborhood at once. Here is what you can safely check yourself, and where to stop.
Start with the obvious, because it is often the answer
Check the thermostat
Set it to HEAT, and set the target at least five degrees above the current room temperature. Battery-powered thermostats fail quietly; if the display is dim or blank, replace the batteries before doing anything else. If the system was recently worked on, confirm the mode is not stuck on EM HEAT or FAN ONLY.
Check the filter
A clogged filter causes more furnace failures than any single component. Restricted airflow lets the heat exchanger overheat, which trips the high-limit switch and shuts the burners down. The blower keeps running, so you get cool air from the vents while the system appears to be working. Hold the filter to a light. If you cannot see through it, replace it.
Check the breaker and the switch
Furnaces have a dedicated breaker, and most also have a service switch nearby that looks exactly like a light switch. It gets flipped off during attic work and forgotten. Check both.
Check the gas supply
If you have gas appliances elsewhere, confirm they work. If your stove will not light either, the issue is the gas supply, not the furnace.
Check the condensate drain
High-efficiency condensing furnaces produce water and have a drain and trap. When that blocks, a pressure switch or float safety shuts the furnace down. A slow drip from the furnace cabinet or standing water in the pan points at this.
Check the vents and returns
Closed supply registers and blocked return grilles create the same airflow restriction as a dirty filter. Open everything and pull furniture away from the return.
Stop here and call if any of this is true
- You smell gas anywhere in the house. Leave and call the gas utility first.
- There is a persistent burning, plastic, or electrical smell.
- The breaker trips again after you reset it once.
- You see soot around the furnace or the vent connections.
- The burner flames are yellow and lazy rather than steady blue.
- There is a loud boom or bang when the burners light.
Those are combustion and safety issues. Shut the system off at the breaker and call (833) 435-6611.
What the technician will check that you cannot
Fault codes
Modern furnaces store diagnostic codes and flash them on an LED behind the access panel. Reading them correctly requires the manufacturer's code table, and the same blink pattern means different things across brands.
The ignition sequence
A gas furnace follows a fixed sequence: thermostat calls, inducer starts, pressure switch closes, igniter glows, gas valve opens, flame sensor proves the flame, blower starts. A technician watches that sequence and identifies precisely where it breaks down. Failure at the igniter, the flame sensor, the pressure switch, or the gas valve produces different symptoms at different points.
Temperature rise
Every furnace has a specified temperature rise range on its data plate, typically 30 to 60 degrees. Measuring the actual rise across the heat exchanger reveals airflow problems that no visual inspection would catch. Too high means restricted airflow. Too low often means an oversized blower or a duct leak pulling in attic air.
Heat exchanger inspection
Cracks in a heat exchanger allow combustion gases into the supply air. Inspection means a camera and, sometimes, partial disassembly. It is the one furnace finding that ends the repair conversation immediately. Details on furnace repair.
Why furnaces short cycle
Short cycling, where the furnace runs for a few minutes then shuts off repeatedly, is nearly always overheating from restricted airflow. The high-limit switch is doing its job. Replacing the limit switch without correcting the underlying restriction simply resets the countdown.
The restriction is usually a dirty filter, a dirty blower wheel, undersized return ductwork, or crushed flex duct in the attic. Fixing the airflow fixes the cycling. Read more about HVAC repair and airflow diagnostics.
For a no-heat call at any hour, call (833) 435-6611, or find your Texas city.
Need a technician? Call (833) 435-6611 any hour of the day, or find your Texas city for local service details.
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