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Problem My Air Conditioner Is Not Cooling My House? 20 Reasons Why

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Problem: We have many people ask us this general question, “Why is my air conditioner not cooling my house? I set my thermostat on 72 and our AC never reaches the 72-degree temperature!”

Answer: There are many reasons why your air conditioner or heat pump might not be cooling your home properly. We have a really good YouTube video made by Word of Advice TV that explains in detail 20 reasons why that an air conditioner or heat pump will not cool your home. Thanks so very much to Word of Advice TV for making this great video! I list the 20 reasons below, but the video does a much better job of explaining.

Here are the 20 reasons:

  1. Outdoor unit not running at all. Please click here to see how to troubleshoot when the AC will not come on at all. 
  2. The unit has a bad, weak, or dead capacitor. Please click here to see the new capacitors that we sell.
  3. The unit has a locked-up compressor.  We sell compressor hard start boosters that might help free a locked up compressor on the following page: Please click here to see the compressor hard start boosters that we sell. 
  4. The unit has a bad condenser fan motor. We sell condenser fan motors on the following page: Please click here to see the condenser fan motors that we sell: 
  5. A dirty furnace or a dirty air handler filter. A dirty filter will restrict airflow and cause freeze-ups and other problems.
  6. A plugged or dirty evaporator coil. If the evaporator coil is dirty it will restrict airflow and cause freeze-ups. Many coils will accumulate dirt, lint and hair on the underside of the coil. The evaporator coil needs to be inspected and cleaned if dirty. Please click here if you are interested in some evaporator coil cleaner that we sell.
  7. A dirty outdoor condenser coil. If the outdoor coil is dirty it will cause the unit to run at high pressure and cooling will be greatly reduced! We need to have a clean condenser coil for the AC unit to be able to do its job and run properly. Please click here if you are interested in some condenser coil cleaner that we sell. 
  8. Dirty return grill. Make sure that your air conditioner return registers are not blocked with furniture, dirty, or lint.
  9. Bad or malfunctioning thermostat or thermostat batteries. Yes, make sure that the batteries are in good condition.
  10. Programmable thermostat problem where the programmable thermostat is not set to the right program. This makes you feel like the thermostat has a mind of its own or is haunted! Ha! To over-ride most programmable thermostats just push the “Hold” button and then the desired temperature that you want.
  11. The homeowner waits too long to turn the AC on and the AC can not catch up in cooling the home for a long time because the home started out too hot. For example, If a homeowner waits until the home gets to 85 degrees on a 95-degree day then it can cause the AC to run probably all day long and most of the night to cool the home down.
  12. The unit is low on Freon or refrigerant. Of course, the AC can not cool properly if the unit is low on refrigerant charge. You or a service tech would need to attach gauges and temp sensors to make sure that your unit is charged properly.
  13. Leaks in the ductwork can cause the air conditioner to not cool properly. We would suggest inspecting your ductwork to make sure there are no leaks in the ductwork. You may need to go into the attic, crawl space, or basement to inspect the ducts. We sell some really good foil duct tape on the following page: Please click here if you would like to see the duct tape that we recommend and sell.
  14. An under-sized unit can cause a unit to not cool properly. A Manual J heat gain and heat loss calculation should be completed before any air conditioning system is installed. The Manual J calculation will tell the homeowner how much heat is lost in the wintertime and how much heat is gained in the wintertime so the homeowner and contractor can install the right size furnace and air conditioner.  The Manual J calculations take into consideration many variables that are calculated on most of the time a computer program the contractor has. The Manual J calculation considers the number of windows, doors, what kind of windows and doors, the R values, the amount of insulation, which direction the home is facing, and whether or not the home is brick or vinyl siding.  This Manual J calculation is very important so that the homeowner knows he/she is getting the right size furnace and air conditioner.
  15. An Air to Air or HVR (heat vent recovery) system that is running all the time can cause a home to not cool properly. If you have an HVR system I would recommend making sure that it is running properly.
  16. Open windows or doors. This is common sense to have windows and doors closed. Heat travels from hot to cold so if a door or window is open the outdoor heat will seak to enter a cool house.
  17. A bad air conditioning installation job or a hack job where the contactor or installer did not know what they were doing and did not install the AC system right.
  18. Bad zone controllers or bad dampers. Make sure that if you do have zone controllers and dampers that they are opening and closing properly. If you have a manually controlled damper like in the pictures below make sure that the dampers are open on all your duct runs so that air can circulate through the duct and into your home. Many times I will find that the dampers are loose and have become closed thus restricting airflow! On most round duct dampers if the handle is parallel with the duct run then the damper is open. If the handle is perpendicular with the duct run then the damper is closed.

19. A poorly vented attic where the roof vents are stopped up with insulation or are nonexistent. A poorly vented attic causes a tremendous build of heat that can be transferred into the homes living space. Make sure that the attic is vented properly.

20. A poorly insulated house can cause heat to enter and leave the home. Make sure that you have enough insulation in your home to stop so much heat gain in the summer and heat loss in the winter.


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