Questions & answers on how to buy, diagnose, repair air conditioners & heat pumps:

This air conditioner & heat pump inspection, installation, diagnosis & repair FAQ series lists questions & answers sorted by major air conditioning or heat pump topic.

Page top photo: a pair of start/run capacitors on the outdoor compressor/condenser unit of an air conditioning system.

This article series describes how to inspect and repair all types of residential air conditioning systems (A/C systems). Information for home buyers, owners, and home inspectors about A/C or heat pump system problems.

Air Conditioning or Heat Pump System FAQs Master List

The questions and answers immediately below were posted originally

at AIR CONDITIONING & HEAT PUMP SYSTEMS - home. Be sure to see the recommended topics and articles given on that page.

Image: a Supco RLC051 "dry" trap for HVAC condensate lines can reduce clogging problems. We discuss this waterless trap as an alternative to P-traps in a reader Q&A below on this page.

Here we list all the HVAC A/C and heat pump FAQs ( often these pages also containing their own index to additional detail).

Article Contents

• A/C HEAT PUMP CONTROL / SWITCH FAQs
• A/C HEAT PUMP CONTROL / SWITCH FAQs-2
• A/C HEAT PUMP CONTROL / SWITCH FAQs-3
• A/C SERVICE CALL CHARGES or ADVICE FAQs - do I really need a new A/C system?
• AIR CONDITIONER TEMPERATURE FAQs
  • TEMPERATURE READING, ABNORMAL FAQs
  • TEMPERATURE READING, NORMAL FAQs
  • TEMPERATURE READING FAQs, OTHER
• AIR CONDITIONER / HEAT PUMP BREAKER / FUSE FAQs
• AIR CONDITIONER / HEAT PUMP COMPONENT FAQs
• AIR CONDITIONER / HEAT PUMP ELECTRICAL PROBLEM FAQs
• AIR CONDITIONER / HEAT PUMP LOST COOLING DIAGNOSTIC FAQs - A/C or heat pump not working
• AIR CONDITIONER / HEAT PUMP LOST COOLING CAPACITY FAQs - second page of the topics just below
• A/C or HEAT PUMPS in MOBILE HOMES
• A/C TAKES TOO LONG TO COOL MY HOME
• BTU RATING Q&A
• COLD WEATHER CONTROLS
• DEHUMIDIFICATION / HUMIDITY PROBLEMS
• DUCTWORK ISSUES
• LOST COOLING CAPACITY FAQs - A/C blows warm air or doesn't cool enough or doesn't cool some areas
• REPAIR vs REPLACE AIR HANDLER BLOWER UNIT FAQs - replace the evaporator coil, replace the whole unit?
• REPAIR vs REPLACE COMPRESSOR / CONDENSER UNIT FAQs - repair vs replace?
• SWITCH BETWEEN COOL & HEAT MODE FAQs
• WEAK COOLING CAPACITY FAQs
• WON'T RUN or SHUTS DOWN FAQs
• AIR CONDITIONER / HEAT PUMP SERVICE VALVE FAQs
• AIR CONDITIONER / HEAT PUMP STARTS AFTER TURNING OFF FAQs
• AIR CONDITIONER / HEAT PUMP TEMPERATURE FAQs
  • REFRIGERANT LINE TEMPERATURE FAQs - which refrigerant piping lines are hot when
  • TEMPERATURE READING, ABNORMAL FAQs
  • TEMPERATURE READING, NORMAL FAQs
  • TEMPERATURE READING FAQs, OTHER
  • COMPRESSOR CONDENSER TEMPERATURE & PRESSURE FAQs
  • CONDENSER TEMPERATURE FAQs
  • EVAPORATOR COIL TEMPERATURE FAQs
  • ROOM TEMPERATURE VARIATION FAQs - indoor air temperatures
• AIR CONDITIONER / HEAT PUMP WON'T START FAQs
• AIR CONDITIONER / HEAT PUMP STARTS AFTER TURNING OFF FAQs
• AIR CONDITIONER / HEAT PUMP NEW UNIT WON'T START FAQs
• AIR HANDLER / BLOWER UNIT WON'T START FAQs - or won't keep running
• COMPRESSOR/CONDENSER UNIT WON'T START FAQs - outdoor unit
• CONTACTOR RELAY WON'T START FAQs
• INTERMITTENT A/C HEAT PUMP WON'T START FAQs
• NEW A/C or HEAT PUMP WON'T START FAQs
• SWITCHES TURN OFF A/C or HEAT PUMP FAQs
• UNIT RUNS In EITHER COOL or HEAT but NOT BOTH FAQs
• AIR CONDITIONER / HEAT PUMP WON'T STOP FAQs
• AIR CONDITIONING HEAT PUMP REPAIR FAQs
• AIR FILTER FAQs 
  • AIR FILTER POSITION & AIRFLOW FAQs - which side faces the blower?
  • AIR FILTER DAMAGED or DIRTY FAQs
  • AIR FILTER LOCATION FAQs
  • AIR FILTER SIZE FAQs
  • DIRTY AIR FILTER PROBLEMS-FAQs
  • OTHER AIR FILTER FAQs - electrostatic filter clicking
• AIR HANDLER / BLOWER UNIT FAQS
  • AIR H ANDLER / BLOWER UNIT BLOWS FUSE or TRIPS BREAKER FAQs
  • AIR HANDLER / BLOWER UNIT FAN REPAIR FAQs - Rodent damage, Blown Fuses, Door safety, switch voltage, Repair vs replace parts
  • AIR HANDLER / BLOWER UNIT FAN RUNS BACKWARDS FAQs
  • AIR HANDLER / BLOWER UNIT FAN WONT STOP FAQs
  • AIR HANDLER / BLOWER UNIT SPEED FAQs
  • AIR HANDLER / BLOWER UNIT NOISE FAQs
  • AIR HANDLER / BLOWER UNIT RUNS for NO REASON FAQs
  • AIR HANDLER / BLOWER UNIT WON'T START FAQs - or won't keep running
  • AIR HANDLER STARTS AFTER TURNING OFF FAQs
  • AIR HANDLER / BLOWER UNIT WON'T STOP FAQs
  • BLOWER FAN ASSEMBLY CLEANING FAQs
  • BLOWER FAN OPERATION & TESTING FAQs
  • BLOWER FAN OPERATION & TESTING FAQs-2 - damaged fan blades, fan size, signs of electrical failures
  • BLOWER FAN OPERATION & TESTING FAQs-3
  • BLOWER LEAKS, RUST & MOLD FAQs - water leaking out of or mold growing in the air handler
  • FROST BUILD-UP on AIR CONDITIONER COILS FAQs - at the indoor air handler
  • REPAIR vs REPLACE AIR HANDLER BLOWER UNIT FAQs - replace the evaporator coil, replace the whole unit?
  • SWITCHES TURN OFF A/C or HEAT PUMP FAQs
  • UNIT RUNS but CAN'T COOL the BUILDING FAQs
  • UNIT RUNS but CAN'T HEAT the BUILDING FAQs
  • WEAK or WARM AIR from AIR CONDITIONER FAQs
• AIR FLOW MEASUREMENT FAQs
• AIR FLOW, NONE at SUPPLY REGISTERS FAQs
• AIR FLOW OBSTRUCTION IN TO AIR HANDLER FAQs
• AIR FLOW at RETURN AIR INLET REGISTERS FAQs
• AIR FLOW TOO WARM at SUPPLY REGISTERS FAQs - hot in house cool in attic or crawlspace?
• AIR FLOW TOO WEAK at SUPPLY REGISTERS FAQs
• AIR FLOW OBSTRUCTION IN TO AIR HANDLER FAQs
• CAPACITOR FAQs - also see HVAC CAPACITOR DIAGNOSTIC FAQs
• CLEARANCE DISTANCE, HVAC FAQs
• COMPRESSOR / CONDENSER DIAGNOSTIC FAQs
  • COMPRESSOR / CONDENSER UNIT BLOWS FUSE or TRIPS BREAKER
  • COMPRESSOR / CONDENSER UNIT COOL with AIR or WATER? FAQs - spray or immerse in water as a diagnostic or to improve efficiency
  • COMPRESSOR / CONDENSER DIAGNOSTIC FAQs - spray with water?, energy use monitors, phased zone heat pumps
  • COMPRESSOR / CONDENSER SHORT CYCLING FAQs - shuts off, short cycles, hard start, won't start, won't run, won't stop running, oil problems
  • COMPRESSOR / CONDENSER DIAGNOSTIC FAQs-3 - Service call charges vs work done, Electrical failures, Weak or warm air flow
  • COMPRESSOR / CONDENSER UNIT FAN WON'T RUN or WON'T STOP FAQS - or runs backwards
  • COMPRESSOR / CONDENSER UNIT FROST & ICE FAQs
  • COMPRESSOR / CONDENSER UNIT ELECTRICAL FAILURE FAQs - other than blowing fuses
  • COMPRESSOR / CONDENSER UNIT FROST or ICE FAQs - at the outdoor unit, defrost cycle, water
  • COMPRESSOR / CONDENSER UNIT HARD START
  • COMPRESSOR / CONDENSER UNIT SHUTS OFF or WON'T KEEP RUNNING FAQs - A/C or heat pump turns off unexpectedly
  • COMPRESSOR / CONDENSER UNIT WON'T START or WON'T RUN FAQs
  • COMPRESSOR / CONDENSER UNIT WON'T STOP RUNNING FAQs
  • INTERMITTENT A/C HEAT PUMP WON'T START FAQs
  • PHASED ZONE HEAT PUMP EFFICIENCY FAQs
  • SHORT CYCLING AC COMPRESSOR FAQs
  • TIGHT or SEIZED AC COMPRESSORS-FAQs
  • UNIT RUNS DURING DAY but NOT AT NIGHT FAQs
  • UNIT RUNS In EITHER COOL or HEAT but NOT BOTH FAQs
  • UNIT RUNS but AIR IS NOT COOL FAQs
  • UNIT RUNS but CAN'T COOL the BUILDING FAQs
  • UNIT RUNS but CAN'T HEAT the BUILDING FAQs
  • WEAK COOLING CAPACITY FAQs
  • WON'T RUN or SHUTS DOWN FAQs
• COMPRESSOR CONDENSER FAN REPAIR FAQs
  • CONDENSER FAN DIAGNOSTIC FAQs
  • CONDENSER FAN MOTOR / MOTOR CAPACITOR FAQs
  • CONDENSER FAN NOISE FAQs
  • CONDENSER FAN RUNS BACKWARDS FAQs
  • CONDENSER FAN SPEED FAQs
  • CONDENSER FAN WIRING FAQs
  • CONDENSER FAN WON'T STOP RUNNING FAQs
  • CONDENSER FAN WON'T START FAQs
  • CONDENSER FAN WON'T KEEP RUNNING FAQs - turns off when it shouldn't
  • FAN DIFFERENCE BETWEEN INSIDE AND OUTSIDE FAQs
  • HIT the CONDENSER UNIT CONTROL BOARD, FAN, FAN MOTOR to MAKE IT RUN FAQs
  • ADDITIONAL MISCELLANEOUS HVAC CONDENSER FAN FAQs
• COMPRESSOR / CONDENSER UNIT NOISE FAQs
  • CHIRPING CRICKET NOISE at the COMPRESSOR/CONDENSER FAQs
  • CLANGING RATTLING NOISE at the COMPRESSOR/CONDENSER FAN FAQs
  • CHUGGING NOISE at the COMPRESSOR/CONDENSER FAQs
  • EXPLOSION NOISE & LIGHTS DIM when A/C STARTS FAQs
  • HELICOPTER NOISE at the COMPRESSOR/CONDENSER FAQs
  • HISSING NOISES at the COMPRESSOR/CONDENSER FAQs
  • RATTLING NOISES at the COMPRESSOR/CONDENSER FAQs
  • SCREECHING SOUND at the COMPRESSOR/CONDENSER FAQs
  • SHUDDERING VIBRATING at the COMPRESSOR/CONDENSER FAQs
  • SQUEALING NOISES at the COMPRESSOR/CONDENSER FAQs
  • WHOOSHING AIR NOISES at the COMPRESSOR/CONDENSER FAQs
• COMPRESSOR / CONDENSER REPAIR FAQs
• COMPRESSOR / CONDENSER UNIT REPAIR vs REPLACE FAQs - repair vs replace?
• COMPRESSOR / CONDENSER UNIT FROST & ICE FAQs
• COMPRESSOR CONDENSER MOTOR ROTATION ERROR CODE FAQs
• COMPRESSOR / CONDENSER UNIT UNUSUAL FAQs
• CONDENSER UNIT FAN SPEED FAQs
• CONDENSER UNIT FAN FAQs
• SHORT CYCLING ON & OFF FAQs
• SHORT CYCLING AC COMPRESSOR FAQs
• CONDENSER UNIT WON'T START FAQs
• CONDENSER UNIT STARTS AFTER TURNING OFF FAQs
• CONDENSER UNIT FAN WON'T START FAQs
• CONDENSER UNIT WON'T STOP FAQs
• CONDENSER FAN WON'T STOP RUNNING FAQs
• CONDENSER UNIT WIRING FAQs
• MISCELLANEOUS FAQs - hiding the units, voltage levels
• REPAIR vs REPLACE COMPRESSOR / CONDENSER UNIT FAQs - repair vs replace?
• CONDENSATE DRAIN PROBLEM FAQs
  • CONDENSATE DISPOSAL into APPLIANCE DRAIN PAN FAQs - into a water heater or washer leak catch-pan?
  • CONDENSATE DISPOSAL INTO PLUMBING FIXTURE FAQs
  • CONDENSATE DRAIN BLOCKED or CLOGGED FAQs
  • CONDENSATE DRAIN INSULATION FAQs
  • CONDENSATE DRAIN REPAIR FAQs - broken or missing, clogs, slope, traps
  • CONDENSATE DRAIN SIZE FAQs
  • CONDENSATE DRAIN TRAP FAQs
  • CONDENSATE NOT DRIPPING INTO DRAIN PAN, FAQs
  • DRIPPING NOISE FAQs
  • OUTDOOR CONDENSATE DISPOSAL FAQs
• CONDENSATE HANDLING FAQs
  • CONDENSATE BLOWS OFF EVAPORATOR COIL FAQs
  • CONDENSATE DRAIN CLEANOUT or DE-CLOG FAQs
  • CONDENSATE DRAIN FREEZE PROTECTION FAQs
  • CONDENSATE DRAIN LEAK FAQs - water on the floor, condensate on the drain line
  • CONDENSATE DRAIN PROBLEM FAQs
  • CONDENSATE DRAINAGE VOLUME FAQs - too much or too little condensate
  • CONDENSATE OVERFLOW PAN & PIPING FAQs - why two drain lines? overflow pan switch, size, routing, connections
• CONDENSER FAN, COMPRESSOR / CONDENSER DIAGNOSTIC FAQs
• CONDENSER CONTROL BOARD HIT to MAKE FAN RUN FAQs
• CONDENSER FAN FAQs
• CONDENSER FAN SPEED FAQs
• CONDENSER FAN WIRING FAQs
• CONDENSER FAN WON'T STOP RUNNING FAQs
• CONDENSER FAN WON'T START FAQs
• CONDENSER FAN WON'T KEEP RUNNING FAQs - turns off when it shouldn't
• CONDENSER FAN DIAGNOSTIC FAQs
• CONDENSER FAN MOTOR / MOTOR CAPACITOR FAQs
• CONDENSER WIRING DAMAGE FAQs
• CONDENSING COIL REPAIR REPLACE FAQs
  • COST to REPLACE an A/C COIL, FAQs
  • CORROSION FAQs
• CONTACTOR RELAY DIAGNOSIS & REPAIR FAQs
• COOLING COIL FAQs
• COOLING COIL / EVAPORATOR COIL FAQs #2
• DIRTY COOLING COIL / EVAPORATOR COIL FAQs
• FROST BUILD-UP on AIR CONDITIONER COILS FAQs
• DATA TAGS on AIR CONDITIONERS FAQs
• DEHUMIDIFICATION BASIC FAQ
• DUCTWORK FAQs
  • AIR LEAKS in DUCTWORK FAQs
  • DUCT & AIR FLOW PROBLEM FAQs
  • DUCT DAMAGE, MECHANICAL, FAQs
  • DUCT SYSTEM & DUCT DEFECT FAQs
  • DUCT SYSTEM & DUCT DEFECT FAQs-2
  • RETURN AIR IMPROVEMENT FAQs
  • RETURN AIR INCREASE FAQs
  • RETURN AIR REGISTER & DUCT FAQs
  • WATER & ICE IN DUCT WORK FAQs 
  • WET CORRODED DUCT WORK FAQs
• ELECTRICAL PROBLEM at A/C or HEAT PUMP FAQs
• ENERGY USE MONITORS for HVAC SYSTEMS FAQs
• FURNACE or AC BLOWER FAN WONT STOP FAQs
• HEAT PUMP ELECTRICITY COST FAQs
• HEAT PUMP REPAIR FAQs
• HEAT PUMP OUTDOOR UNIT DEFROST CYCLE FAQs
• HVAC SYSTEM NOISE DIAGNOSIS FAQs - index to HVAC noise description & troubleshooting questions and answers
  • BANGING NOISES at HVAC SYSTEMS, FAQs - reader descriptions, Q&A
  • BUZZING NOISES at HVAC SYSTEMS, FAQs
  • CLICK CLANK TAPPING NOISES at HVAC SYSTEMS, FAQs
  • GRINDING NOISE at HVAC EQUIPMENT, FAQs
  • HAMMERING, POPPING NOISES at HVAC EQUIPMENT, FAQs
  • HUMMING NOISES at HVAC EQUIPMENT, FAQs - including vibration sounds
  • KNOCKING SOUNDS at HVAC EQUIPMENT, FAQs
  • RATTLING NOISES at HVAC EQUIPMENT, FAQs
  • SCREAM, SCREECH, SHRIEKS, SQUEAL, WHISTLE, WHINE at HVAC EQUIPMENT, FAQs
  • STRAINING NOISES at HVAC EQUIPMENT, FAQs
  • THUMPING THUNDER NOISES at HVAC EQUIPMENT, FAQs
  • VIBRATION NOISES at HVAC SYSTEMS, FAQs
  • WATER SOUNDS, RUSHING WATER NOISES at HVAC SYSTEMS, FAQS
  • WHISTLING NOISE at HVAC EQUIPMENT, FAQs
  • WHOOSHING WIND NOISE at HVAC SYSTEMS, FAQs
  • WOOD CHIPPER NOISE at AC SYSTEM, FAQs
  • WOOING NOISES at HVAC EQUIPMENT, FAQs
• LOST COOLING CAPACITY FAQs - A/C blows warm air
• MULTI-AQUA CHILLED WATER SYSTEM PIPING FAQ
• ODORS in HVAC SYSTEMS, FAQs
• REFRIGERANT HIGH HEAD PRESSURE DIAGNOSTIC FAQs
• REFRIGERANT LEAK REPAIR FAQs
  • REFRIGERANT LEAK CAUSE FAQs
  • REFRIGERANT LEAK LOCATION & DIAGNOSIS FAQs
  • REFRIGERANT LEAK REPAIR COST & SERVICE ISSUE FAQs - cost & success & multiple visits?
  • REFRIGERANT LEAK REPAIR METHOD FAQs - solder, glue, or other ways to fix a leak
• REFRIGERANT LINE FROST FAQs
• REFRIGERANT OIL PROBLEM FAQs
• REFRIGERANT PIPING INSULATION FAQs
• REFRIGERANT PIPING INSTALLATION FAQs-2
• REFRIGERANT PRESSURE READING & CHART FAQs
• REFRIGERANT TEST GAUGE FAQs
• REFRIGERANT UNDER CHARGE EFFECTS FAQs
• RELAY CONTACTOR DIAGNOSIS & REPAIR FAQS
• STAINS HVAC SOOT or DUST FAQs
• SWITCH BETWEEN COOL & HEAT MODE FAQs
• SWITCHES TURN OFF UNIT FAQs
• TEMPERATURE & PRESSURE FAQs
• THERMOSTAT CALIBRATION FAQs - thermostat accuracy, temperature control
• THERMOSTATS, DIAGNOSTIC FAQs - repair or replace
• THERMOSTATS, DIAGNOSTIC FAQs-2
• THERMOSTATS, DIAGNOSTIC FAQs-3
• THERMOSTATS, DIAGNOSTIC FAQs-4
• THERMOSTAT SWITCH FAQs
• FAN SWITCH SETTING FAQs - at the thermostat, fan won't run, fan won't stop
• HEAT WON'T TURN ON FAQs
• HEAT WON'T TURN OFF FAQs
• MISCELLANEOUS THERMOSTAT SETTING FAQs
• THERMOSTAT WIRE CONNECTION FAQs
• THERMOSTATIC EXPANSION VALVE FAQs TXV TEV
• WEATHER IMPACT & STORM DAMAGE to A/C or HEAT PUMP FAQs

...

...

Continue reading at AIR CONDITIONING & HEAT PUMP SYSTEMS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AIR CONDITIONER BLOWS WARM AIR
• AIR CONDITIONER WON'T START
• AIR CONDITIONING & HEAT PUMP SYSTEMS - home
• AIR CONDITIONER / HEAT PUMP OPERATION - how does an air conditioner or heat pump actually work?
• AIR CONDITIONER TEMPERATURE MEASUREMENT
• AIR HANDLER / BLOWER UNITS - home
• COMPRESSOR / CONDENSER REPAIR - home
• COMPRESSOR / CONDENSER DIAGNOSTICS
• CONTROLS & SWITCHES on A/C or HEAT PUMP - what and where are all of the controls?
• DIAGNOSTIC GUIDE A/C or HEAT PUMP - first steps to diagnose an air conditioner or heat pump
• DIAGNOSTIC DETAILS A/C or HEAT PUMP - detailed list of diagnostic procedures
• DUCT SYSTEM DESIGN SIZE & DEFECTS - home
• MANUALS & PARTS GUIDES - HVAC - home
• REFRIGERANT LEAK DETECTION
• SPLIT SYSTEM AC / HEAT PUMP REPAIRS

Suggested citation for this web page

AIR CONDITIONING & HEAT PUMP SYSTEM FAQs INDEX - HVAC inspection, installation, diagnosis & repair Q&A provided free at InspectApedia.com or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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