Condenser - Often called the “outside unit” of a split system air conditioner. It can only eject heat in a straight cool air conditioner but, if the system is a heat pump, the refrigerant flow can be reversed so that it absorbs outdoor heat in the winter. The primary components of a condenser are the compressor, the drum-shaped unit in the center, and the condenser coils that wrap around the sides. Condenser Coils - The refrigerant piping with fins that absorb or dissipate heat that wrap around the sides of a condenser unit of a split system.

Evaporator Coils - The refrigerant piping with fins that absorb or dissipate heat in the air handler of a split system.

Float Switch - A device that prevents the leakage of condensate water from the backup from an air handler when the condensate drain line clogs by shutting off the system. A float switch can also be installed at the side of an auxiliary drain pan to shut off the system when the pan fills with leaking water.

Heat Exchanger - A heat exchanger is the part of the system that transfers heat from the hot parts of the machine or a system to the cold parts of the machine or system. It is the part of a furnace that encloses the burners to transfer heat to the air air flow around it while excluding combustion gases. In a heat pump or air conditioner, it is the condenser and evaporator coils.

Heat Pump - An air conditioning system that is able to reverse the flow of refrigerant through the system so that it can both cool and heat.

Humidistat - Similar to a thermostat except that it maintains interior humidity level, instead of temperature, when controlling an air conditioning system. A humidistat is more energy efficient than a thermostat at maintaining low humidity to avoid mold growth in Florida homes during hot weather when the home is not occupied.

Jump Duct - When a supply register serves a room with a closed door and no return air register, the air flow slows down and pressurizes the room, because it is unable to push air back towards a return air register. A jump duct has a register in the room and connects it to a register in a nearby room that has direct air flow to the air handler or a return air register.

MERV Rating - An acronym for Minimum Efficiency Reporting Value, and is a sliding scale that measures the size particles that an air conditioning filter can trap. A low number like 4 indicates minimum filtration, while 8 and above means the filter will catch much smaller particles. Unfortunately, as the MERV number goes up the resistance to air flow also increases.

Register - The air vents with fins at the termination of ducts. The supply registers that deliver air to a room usually have an adjustment handle to change the angle of the fins, while the return air registers usually have fins that are locked in place.

SEER Rating - An acronym for Season Energy Efficiency Rating, it rates the energy efficiency of an air conditioner or heat pump system. Older systems have a SEER as low as 9, the current mandatory minimum SEER is 14, and 15 to 20 and above indicates a high efficiency system.

Straight Cool - Also referred to as a “cooling” or “standard” air conditioner, it has only one function: utilizing the circular flow of a refrigerant gas to take the heat from inside a home and move it outside. Unlike a heat pump, it cannot also absorb outdoor heat and move it into the home.

Temperature Differential - The difference between the temperature of the air going into evaporator coils and temperature of the air coming out. In other words, how much it cools the air. Also called the “Delta T” by HVAC professionals. For example, you would subtract an outgoing air temperature of 56º from an incoming temperature of 74º to arrive at an 18º differential.

Transfer Grille - A grille, usually over a doorway, that provides an opening from the bedroom to the adjacent hallway for air to return back to the air conditioning air handler or furnace when the supply register (vent) in the ceiling of the bedroom is blowing conditioned air into the room.

UV Air Purifier - Sometimes referred to as a “UV filter,” although the device does not does not trap particles in the air like a regular air filter. It is an ultraviolet light in a duct near the air handler that kills germs passing by in the air flow, and most have a sensor that only activates the light when the blower is on.

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

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

  3. Why is my air conditioner not cooling enough?

  4. How can I find out the SEER of my air conditioner?

  5. What is wrong with an air conditioner when the air flow out of the vents is low?

  6. Why are some rooms cooler or warmer than others?

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

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

  4. What color should the flame be in a natural gas furnace?

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

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

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

  8. How can checking the fireplace damper reduce energy bills year-round?

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

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

  11. What is an HVAC system?

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

  13. What does an ultraviolet air treatment system do?

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

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

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

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

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

  19. What is a geothermal heat pump?

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

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

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

  23. Should I move my air conditioner into the attic?

  24. What are the minimum requirements for bathroom ventilation?

  25. What is an air conditioning heat recovery system?

  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. What is the average lifespan of an air conditioner?

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

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

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

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

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

  34. What are the most common problems with wall/window air conditioners?

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

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

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

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

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

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

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

  42. What is a FanRecycler and AirCycler?

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

  44. Why has the thermostat screen gone blank?

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