AC Not Cooling Your House? 8 Things to Check
It is 95 degrees in Fort Collins and your AC is running, but your house is not getting any cooler. Before you call for emergency service, work through these eight checks. You might save yourself a service call.
1. Check Your Thermostat
Make sure your thermostat is set to COOL (not HEAT or OFF) and that the temperature is set lower than the current room temperature. Verify the fan is set to AUTO rather than ON. If the batteries are low on a wireless thermostat, it may not communicate properly with your system.
2. Check the Air Filter
A clogged air filter is the single most common reason an AC struggles to cool. When air cannot flow freely through the filter, the system cannot pull enough warm air across the evaporator coil to cool it. In extreme cases, the coil freezes solid and the system stops cooling entirely. Pull out the filter. If it looks gray or matted, replace it and give the system 30 minutes to recover.
3. Check the Outdoor Unit
Walk outside and look at your condenser unit. Is it running? If the fan is not spinning, you may have a capacitor or contactor issue. Even if it is running, check for debris. Cottonwood fluff is a major problem in Northern Colorado. It coats the condenser fins and blocks airflow. Grass clippings, leaves, and dirt do the same thing. Gently spray the unit with a garden hose to clear the fins. Keep plants and mulch at least two feet from the unit.
4. Check Your Vents
Walk through your house and make sure all supply vents are open and unblocked. Furniture, curtains, and rugs can block vents and restrict airflow. Closing too many vents actually makes your system work harder, not easier. Keep at least 80% of your vents open at all times.
5. Check the Circuit Breaker
Your AC system uses two breakers: one for the indoor air handler/furnace and one for the outdoor condenser. If either has tripped, part of your system is not running. Check your electrical panel and reset any tripped breakers. If a breaker trips again immediately, do not keep resetting it. Call a technician.
6. Look for Ice on the Lines
Check the copper refrigerant lines running from your outdoor unit to your indoor unit. If you see ice or frost on these lines or on the indoor coil, your system has a problem. The most common causes are low refrigerant or restricted airflow (dirty filter, closed vents). Turn off the AC and run the fan only to thaw the ice. This can take several hours. If the issue comes back after you replace the filter and open all vents, you likely have a refrigerant leak that needs professional repair.
7. Check the Drain Line
Your AC removes humidity from the air, and that water drains through a condensate line (usually a PVC pipe near your indoor unit). If this line clogs, a safety switch shuts down your system. You can usually clear the line by pouring a cup of white vinegar down it. In humid summers, algae growth is a common cause of clogs in Loveland and Greeley area homes.
8. Consider the Temperature Differential
A properly working AC should cool air 15 to 20 degrees between the return air (air going in) and the supply air (air coming out of the vent closest to the unit). Hold a thermometer at the return vent and then at the closest supply vent. If the difference is less than 15 degrees, your system is not cooling effectively and likely needs professional service.
When These Checks Do Not Fix It
If your AC still is not cooling after checking all eight items, the problem is likely one of these:
- Low refrigerant: Your system has a leak and needs professional repair and recharging.
- Failed compressor: The heart of your AC system. This is a major repair or replacement situation.
- Bad capacitor: A common and relatively inexpensive fix. The capacitor helps start the compressor and fan motors.
- Undersized system: If your AC has never cooled your home well, it may be too small for the space.
- Duct leaks: Cool air escaping into your attic or crawlspace before reaching your rooms.
Mountain States Mechanical provides AC repair across Windsor, Fort Collins, Loveland, Greeley, Timnath, Johnstown, Berthoud, Wellington, and Severance. We offer same-day service when scheduling allows and upfront pricing on every call.
Frequently Asked Questions
Why is my AC running but not cooling?
Common causes include a dirty air filter, frozen evaporator coil, low refrigerant, dirty outdoor unit, thermostat issues, or blocked vents. Start with the filter and thermostat, then check your outdoor unit for debris.
How much does AC repair cost in Northern Colorado?
Most AC repairs range from $150 to $600. Refrigerant recharges, capacitor replacements, and fan motor repairs fall in this range. Compressor replacement is more expensive at $1,500 to $2,500. Mountain States Mechanical always provides upfront pricing before work begins.
Can I fix my AC myself?
You can fix simple issues like replacing a dirty filter, clearing debris from the outdoor unit, opening blocked vents, and checking your thermostat settings. Anything involving refrigerant, electrical components, or internal parts should be handled by a licensed HVAC technician.
Why is my AC freezing up?
AC systems freeze when airflow is restricted (dirty filter, blocked vents) or when refrigerant is low. Both cause the evaporator coil temperature to drop below freezing. Turn off the AC and run the fan only to thaw it, then address the root cause.
Should I repair or replace my AC unit?
If your AC is over 10 to 15 years old, uses R-22 refrigerant (which is being phased out), and the repair costs more than 50% of a new unit, replacement is usually the smarter financial decision. Newer units are significantly more efficient, which lowers your monthly energy bills.
Need AC Repair Today?
Same-day AC repair available across Northern Colorado when scheduling allows. We diagnose fast and give you upfront pricing before any work starts.