Photograph of  this unusual attic air conditioning system is an example of
the range of human creativity observed during a career of building inspections Air Conditioner or Heat Pump System Operating Defects & How to Fix Them

  • OPERATING DEFECTS, AIR CONDITIONING - CONTENTS: Air conditioning & heat pump operating defects & what to do
    • Air conditioner won't start, noisy, or short cycling
    • Air conditioner does not produce enough cool air volume or air is not cool enough
    • High air conditioner bills or tripping air conditioner circuit breakers
  • POST a QUESTION or READ FAQs about air conditioner or heat pump operating problem diagnosis and repair

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A/C or heat pump operating defect checklist: how to fix an air conditioner or heat pump that is not operating properly: this A/C diagnosis article lists common air conditioning or heat pump operating defects, tells you what to check, and recommends specific air conditioner or heat pump repair guide articles found at this website.

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Air Conditioning System Maintenance & Operating Defect Diagnosis & Repair Guide: defect checklist

Air conditioner or heat pump basic schematic (C) D FriedmanThis A/C repair article is part of our more extensive air conditioning inspection, diagnosis, & repair document which describes the inspection, diagnosis, and repair of residential air conditioning systems (A/C systems) for home buyers, owners, and home inspectors.

Here we list typical, readily observed, air conditioning system operating defects. Use the links at the left side of any of our pages to find more detailed information about these and other air conditioning system defects, as well as diagnostic and repair procedures.

In our sketch at left and in more detail at AIR CONDITIONING & HEAT PUMP SYSTEMS, the major components of an air conditioning system are described, sketches and photographs are provided, and common defects for each component are listed along with visual or other clues that may suggest a problem or probable failure of A/C components.

Here at OPERATING DEFECTS we take you through the major air conditioning problem symptoms and how to get the air conditioning system working again. At a companion article, LOST COOLING CAPACITY, our focus is on the case in which the air conditioning system seems to be "running" but not enough cool air, or no cool air at all is being delivered to the occupied space. At A/C - HEAT PUMP CONTROLS & SWITCHES we explain the many electrical switches and controls that control an air conditioner or heat pump system. You'll need to check these if your air conditioner won't start.

  • The air conditioning system will not operate at all - it won't start up: If the air conditioning system won't run at all, electrical power may be off, controls may be improperly set, or the system may be inoperative for other reasons. First confirm that the system has electrical power and that all of its control switches and thermostat are set to on and cooling positions. See CONTROLS & SWITCHES and see THERMOSTATS. Keep in mind that there are some hard-to-find switches that could be keeping your air conditioner off, such as a Float Switch on Condensate Tray or a blower MOTOR OVERLOAD RESET SWITCH
  • The air conditioning system operates but does not produce any cool air, or not enough cool air. See LOST COOLING CAPACITY
  • The air conditioning system operates but there is not enough cool air flow at the registers. (see DUCT SYSTEM DEFECTS and see LOST COOLING CAPACITY.)
  • The compressor / condenser outside unit is short-cycling, that is, turning itself on and off rapidly, perhaps every few seconds or minutes rather than producing a normal on-cycle of 10 minutes or longer. (see COMPRESSOR CONDENSER). See FAN, COMPRESSOR/CONDENSER UNIT for help in diagnosing and fixing problems with the outdoor compressor/condenser fan and fan motor.
  • The compressor is noisy, during startup, indicating an operating problem. (see COMPRESSOR NOISES.)
  • The compressor squealed at startup, indicating that service may be needed promptly to prevent possibly costly damage to the system. This repair/maintenance item should not be deferred. (see COMPRESSOR NOISES.)
  • Inside cooling or evaporator coil defects that can be seen by eye: dirty coil, blocked coil, frost on the coil, improperly sized evaporator coil, improper evaporator or cooling coil placement in the system. (See COOLING COIL or EVAPORATOR COIL and also AIR HANDLER / BLOWER UNITS for details.)

    Air flow requirements across the air conditioning evaporator coil: if airflow is weak for any reason (dirty coil, duct system defects, blower fan defects, dirty blower squirrel cage fan), the air conditioning system will not operate properly.

    How many cubic feet of air per minute should move across the evaporator coil? Some experts write that there should be between 350 and 400 cubic feet of air per minute (CFM) moving across the evaporator (cooling) coil for each ton of air conditioner capacity. (One ton = 12,000 BTUH so if your AC unit is a 24,000 BTUH unit it is a "two ton" unit and needs to see 700 to 800 CFM of air across the evaporator coil.

    Some home inspectors and air conditioning service technicians carry a small airflow meter that can actually measure this number with fair accuracy. (The same tool is nice for comparing air flow and balancing air flow at various building supply ducts and registers.

    Evaporator coil cleaning often requires cutting refrigerant lines, removal of the coil and other components for cleaning, and reinstallation, pulling a vacuum on the refrigerant lines, and recharge with refrigerant. Such service and repair may involve significant expense, although there are some "in place" cleaning methods using foams and sprays that are a simpler procedure. (see OPERATING TEMPERATURES.)
  • Dirty air conditioning filters, - a source of increased operating costs. Very dirty filters can eventually block the fan itself, leading to more costly repairs. The filters should be changed monthly when the system is in use. Failure to properly filter dust from the return air supply can load the fan or evaporator coil with dust and prevent proper system operation. Installing a filter is normally a minor expense.

    Dirty, blocked evaporator coils can result in improper system operation, very low output temperatures, low air flow (compensated sometimes by increased fan speed), and sometimes frost on the coil and failure of system components. (see AIR HANDLER / BLOWER UNITS.) (see OPERATING TEMPERATURES.)
  • The air conditioner operates but our electrical bills are too high. (see SEER RATINGS and see DUCT SYSTEM DEFECTS.)
  • The heat pump will provide cool air but does not provide heat when heating is required. (See BACKUP HEAT).
  • The heat pump will provide heat but not cool air when cooling is required. (See BACKUP HEAT).
  • The air conditioner fuse keeps blowing or the circuit breaker trips: could mean a compressor which needs repair or replacement, or it could mean a problem with the unit's electrical wiring, such as use of aluminum wiring combined with bad electrical connections.

    Have your service technician check the condition of the electrical circuit first (that's cheaper than a new air conditioning compressor) and then check the condition of the compressor. See COMPRESSOR CONDENSER for air conditioner compressor diagnosis and repair; and if your air conditioning system electrical wiring is aluminum, review the aluminum wiring hazards at ALUMINUM WIRING HAZARDS & REPAIRS since a serious fire hazard could be present.

How to diagnose and fix an air conditioning system that is not working

Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.

If your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.

  • A/C - HEAT PUMP CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
  • OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume
  • LOST COOLING CAPACITY: what to do when not enough cool air comes out of the system
  • COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units. Also see FAN, COMPRESSOR/CONDENSER UNIT for help in diagnosing and fixing problems with the outdoor compressor/condenser fan and fan motor.
  • AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself
  • DUCT SYSTEM DEFECTS: problems with the air duct system, air filters, supply registers, return air registers
  • A/C REFRIGERANT LEAK DETECTION: how to use a TIF5000 to detect air conditioning refrigerant gas leak
  • A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair - a detailed air conditioning system diagnostic checklist

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