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Air Conditioner or Heat Pump System Operating Defects & How to Fix Them AirCondAPedia © 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

This chapter discusses Air Conditioner or Heat Pump System Operating Defects & How to Fix Them. This chapter 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. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

OPERATING DEFECTS - Air Conditioning System Maintenance & Operating Defect Diagnosis & Repair Guide

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. If readers return to the first chapter or view the A/C chapter index, 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 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: 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.
• 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 was 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)
  
• The compressor was 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 UNIT 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. 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 UNIT.) (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 SYSTEMS.

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

• 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
  • What to check first if there is no cool air or not enough cool air
  • Compressor failure diagnosis: basic checks of the air conditioner compressor
  • Ducts & Air Handler diagnosis: basic checks of the indoor air handler (blower), air ducts, and filter systems
• COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units
• 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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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

AIR CONDITIONING & HEAT PUMP SYSTEMS
AGE of AIR CONDITIONERS & HEAT PUMPS
AIR CONDITIONER BTU CHART
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR CONDITIONER NOT WORKING
AIR FILTERS for HVAC SYSTEMS
AIR HANDLER UNIT
  DIRTY A/C BLOWERS
  DAMAGED COOLING COIL
  DIRTY COOLING COIL
  DIRTY COIL CLEANING PROCEDURES
  FROST BUILD-UP
  BLOWER LEAKS, RUST & MOLD
  ADDING A/C: RETROFIT SIZING
BACKUP HEAT for HEAT PUMPS
BLOWER DOORS & AIR INFILTRATION
BOOKSTORE - Air Conditioning "How To" Books
CLEANING & Legionella BACTERIA
COMPRESSOR & CONDENSING COIL
  INSTALLATION ERRORS
  CONDENSING COIL FINS, SUPPORT PADS
  COMPRESSOR NOISES
  HARD STARTING
  TIGHT or SEIZED AC COMPRESSORS
  COMPRESSOR PRESSURE READINGS
  BURNED-OUT COMPRESSOR
  REPLACING A COMPRESSOR
  A/C CAPACITORS
  MOTOR OVERLOAD RESET SWITCH
CONDENSATE HANDLING
  DRIP TRAY DEFECTS
  CONDENSATE LEAKS
  CONDENSATE PUMPS
  CONDENSATE DRAINS
  CONDENSATE TRAY CLEANING
CONTROLS & SWITCHES
COOL OFF HEAT Thermostat Switch
COOLING CAPACITY, RATED
COOLING COIL or EVAPORATOR COIL
DATA TAGS on AIR CONDITIONERS
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
DEFINITION of Heating & Cooling Terms
DEW POINT TABLE - CONDENSATION POINT GUIDE
DUCT SYSTEMS
DUCTS - Asbestos
DUCT SYSTEM DEFECTS
  ASBESTOS HVAC DUCTS
  DUCT ROUTING & SUPPORT
  BALANCING AIR DUCT FLOW
  FIBERGLASS HVAC DUCTS
  FIRE DAMPERS in DUCTWORK
  GOODMAN GRAY FLEXDUCT
  INCREASING RETURN AIR
  LEAKY DUCT CONNECTIONS
  LOCATION OF REGISTERS & DUCTS
  OWENS CORNING FLEXDUCT
  OWL FLEXDUCT
  RETURN AIR REGISTERS & DUCTS
  SUPPLY REGISTERS, & ZONES
  Transite Pipe HVAC Ducts
  UNDERSIZED RETURN DUCTS
  UNSAFE DUCT OPENINGS
  VIBRATION DAMPERS
  WATER & ICE IN DUCT WORK
  WET CORRODED DUCT WORK
  ZONE DAMPER CONTROLS
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCTS, Asbestos Transite Pipe
DUST FROM HVAC?
FAN AUTO ON Thermostat Switch
HEAT LOSS (or GAIN) in BUILDINGS
HUMIDITY LEVEL TARGET
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS
LOST COOLING CAPACITY
  What to check first
  Compressor failure diagnosis
  Duct & Air Handler diagnosis
MOTOR OVERLOAD RESET SWITCH
OPERATING COST
OPERATING DEFECTS
OPERATING TEMPERATURES
  Air Conditioning System Temperatures
  Instruments Used to Measure A/C Temperatures
  Procedures for Making Temperature Measurements
REPAIR GUIDE for AIR CONDITIONERS
REPAIR & DIAGNOSTIC FAQs for A/C
REFRIGERANTS
  REFRIGERANT LEAK DETECTION
  REFRIGERANT LEAK REPAIR
SEER RATINGS & OTHER DEFINITIONS
SYSTEM OPERATION
THERMOSTATS
THERMOSTATIC EXPANSION VALVES
CRITICAL DEFECTS
Air Conditioning "How To" Books

• Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects" section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and home inspection educator.
• Thanks to Mike Giaquinto and Scott at SJM Inspect for technical editing remarks, 5/16/07
• Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
• Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).

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