than it should to a maintain the desired indoor temperature. Several things
     can cause this, and here are the three most common:

  1. a)A dirty air filter severely cuts down air flow and reduces the cooling ability of the system. Check and replace your air filter, if necessary. The problem might be what we call “the forgotten air filter.” An air filter is usually placed in one of two locations: 1) inside or right next the air handler, or 2) mounted behind the return air register (duct vent). Some homeowners have filters at both locations, and regularly change one of them, but have forgotten—or never knew—about the other one. The forgotten filter clogs completely with dust over time and starves the system of air flow, which makes it struggle and run longer to cool down the home. The culprit is sometimes a filter placed on the side of the bottom of the air handler that is only accessible by the removing the bottom front panel of the unit.

  2. b)If the air filter has become so dirty that it has collapsed and pulled away from the filter slot, or there is no air filter in place, then the fins of the evaporator coils (the chilling surfaces that air flows over) will act as a unintended filter, collecting bits of airborne debris in the tiny gaps between them until enough crud accumulates to severely reduce air flow and act as an insulator between the cool coils and the air around them.  The photo below was taken looking up into the tent shape of an evaporator coil that had become so dirty that the coil surfaces are no longer visible, and the following photo shows what a clean evaporator coil looks like.

    In some air handlers (indoor units) you can pull out the filter located at the bottom of the unit and look up directly into the tent shape of the evaporator coil to check for any dirt/dust accumulation. If not, a service technician can open the unit to examine the coils.
       Unfortunately, cleaning a dirty evaporator coil is an expensive proposition, involving evacuating the refrigerant from the system, disconnecting the coil unit, washing and scrubbing away the dirt in a solvent solution, then reinstalling it  and reloading with refrigerant gas.
       Dirt accumulation at the condenser coil (outside unit) will also reduce the efficiency of your system, and the photo below shows a typical accumulation that needs cleaning.

       But it is rarely a big problem, with one exception: when the exhaust for a clothes dryer blows lint into the immediate area. The building code now requires that dryer vents not terminate near an air conditioning condenser.
  3. c)The gradual leakage of refrigerant from the pressurized lines in the system will reduce the cooling ability down to zero over time. An average HVAC system chills the air coming out of the air handler to about 18º F cooler than the incoming air. But as the temperature split (difference between incoming and outgoing air) begins to descend, the only noticeable change at first is that the system takes longer to cool down the home. For example, if the temperature split drops to 9º F the system will still cool your home but it will run for twice as long—and use twice as much energy—to do it.
       A service technician can check the status of your refrigerant to verify if this is the problem. Because it is a sealed system, any loss of refrigerant indicates a leak; so, adding another shot of gas without locating and fixing the leak will only be a temporary solution.

   A annual maintenance service at a minimum or, as recommended by most HVAC contractors, every six months will catch minor problems before they get out of hand. We recommend it.

While we hope you find this series of articles about home inspection helpful, they should not be considered an alternative to an actual home inspection by a local inspector. Also, construction standards vary in different parts of the country and it is possible that important issues related to your area may not be covered here.
©2015 - McGarry and Madsen Inspection.


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More blog posts about heating and air conditioning:

  1. How can I find out the size of my air conditioner?

  2. How can I find out the age of my air conditioner or furnace?

  3. The coils on my heat pump are covered with ice on cold mornings. What’s wrong with it?

  4. What is the SEER of my old air conditioner?

  5. What is the difference between the “ON” and “AUTO” settings on my thermostat?

  6. What is a “ton” of air conditioning?

  7. How do I find the right size air conditioner for my house?

  8. What is an HVAC system?

  9. What is the difference between the SEER and EER of an air conditioner?

  10. What does an ultraviolet air treatment system do?

  11. The coolant line to the outside unit of my air conditioner is frozen. What's wrong?

  12. What size air conditioner is right for my mobile home?

  13. What is the minimum SEER rating for a new air conditioner?

  14. What does the “AFUE” rating of a furnace mean?

  15. How much life is left in that air conditioner?

  16. Why is there mold around the air conditioning ducts?

  17. What is the difference between a heat pump and a cooling air conditioner?

  18. What is the right MERV number for my air conditioning filter?

  19. What is a geothermal heat pump?

  20. Is it alright to close the air conditioning vents in unused rooms?

  21. Should I move the air conditioner into the attic?

  22. My air conditioner outside unit (condenser) won’t start and is making a humming noise. What’s wrong?

  23. What are the minimum requirements for bathroom ventilation?

  24. What is an air conditioning heat recovery system?

  25. What is the best air conditioner for a mobile home?

  26. When should I switch the thermostat to “EMERGENCY HEAT” for my heat pump air conditioner?

  27. Why does the air conditioner condensate drain line need a trap in it?

  28. Should I remove an old whole house fan or keep it?

  29. What is a jump duct?

  30. My air conditioner won’t turn on What’s wrong?

  31. Is it acceptable for an air conditioning condensate drain line to terminate under the house?

  32. What is the purpose of the vent grille over the bedroom door?

  33. Should I have a return air vent in the master bedroom?

  34. Will closing doors reduce my heating and cooling costs?

  35. How much will I save on my utility bill if I get a new higher SEER air conditioner?

  36. Why is there a wall switch next to the furnace or indoor unit of the air conditioner in the garage?

  37. Which one is better for a home heating system: electric or natural gas?

  38. Why does an air conditioner condenser need to be level?

  39. When does the ban on R-22 air conditioning refrigerant take effect?

  40. Why do the lights dim when the air conditioner turns on?

  41. Why is my air conditioner not cooling enough?

  42. What is a return air plenum for a furnace or air conditioning system?

  43. When is an auxiliary drain pan required under an air conditioner indoor unit (air handler)?

  44. Why does it take so long to cool a house when the air conditioner has been off for a while?

  45. What are the right words to use when talking about a heating and air conditioning system?

  46. What is a ductless mini-split air conditioner?

  47. What is a FanRecycler and AirCycler?

  48. Why is my bathroom vent fan not exhausting enough air?

  49. Why has the thermostat screen gone blank?

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