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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
This article is the start of our series on how to diagnose an air conditioner or heat pump that is not cooling: this article explains how to diagnose and correct air conditioning problems like lost or reduced air conditioner cooling capacity, reduced or no cool air flow, reduced or no actual lowering of the air temperaturer, or an air conditioner that won't start.
First try our air conditioner checklist just below - try these steps before calling your HVAC service company.
If not enough cool air is provided by your air conditioner, or if the air temperature is not cool enough, or if you just can't get your A/C unit running, this article helps diagnose and correct the problem with step by step things to check and links to more detailed explanation when you need it.
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If your air conditioner or heat pump is a split system or mini split system design (using a wall-mounted cooling or heating unit) our troubleshooting diagnostics are at SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS.
Is there no cool air at all coming out of the supply registers?
Or is there air blowing out of the supply registers but it's not cool enough?
Here we explain how to diagnose loss of air conditioning cool air flow or cool air temperature.
Before ordering an expensive air conditioner service call to restore lost cooling capacity, here are a few simple steps to perform. Some of these can be done by any homeowner, others may require a bit more expertise.
Below we provide first a very basic Air Conditioning or Heat Pump Diagnostic Checklist, followed by more detailed descriptions of common problem cooling system topics.
Following the checklist we provide more detailed descriptions, photos, and links to in-depth air conditioning inspection, diagnosis, and repair or improvement advice.
Where to start: check that the air conditioning equipment is turned on, the thermostat is calling for cooling, and that the blower unit or air handler is actually blowing air through the ductwork. Details of how to proceed in figuring out what's wrong with your air conditioner begin just below.
If the air conditioning system is not running at all:
If the air conditioning system is still not working, or if the A/C system is running but cool air is not coming out of the supply registers you probably need to call a service technician, but below are some things to check further yourself.
If At Least Some of the Air Conditioner or Heat Pump Equipment is Running but Cool Air is Not Being Delivered - 5 Quick Diagnostic Air Conditioning / Heat Pump System Checks to Get the Air Conditioner Running Again
The basic air conditioning diagnostic checks just below are followed by more detailed investigation of why the air conditioner is not working. But unless you already have a good idea of what's not working, start with these five steps.
If the air conditioning system is still not working, or if the A/C system is running but cool air is not coming out of the supply registers you probably need to call a service technician, but here are some things to check further yourself. Just after these checks we discuss what to do if the air conditioner is running but air flow is too weak (A/C Flow Too Weak) or too warm.
Step 1: Check the Outside Air Conditioning /Heat Pump Compressor-Condenser unit
Is the outdoor compressor-fan unit (COMPRESSOR & CONDENSING COIL) running?
If you cannot find your air conditioner controls and switches see A/C - HEAT PUMP CONTROLS & SWITCHES - list of controls and switches found on air conditioners and heat pumps
Also check the compressor/condenser outdoor fan and fan motor
Condensing unit fan diagnostics: at FAN, COMPRESSOR/CONDENSER UNIT we explain the diagnosis of problems with the compressor/condenser fan and fan motor.
Also see ELECTRIC MOTOR DIAGNOSTIC GUIDE.
At BURNED-OUT COMPRESSOR we explain that if the condensing unit fan is not working the compressor itself may shut down or even be ruined by overpressure or over temperature. Also see NOISES, COMPRESSOR CONDENSER where some noise problems are traced to the cooling fan .
Step 2: Check the Air Conditioning /Heat Pump Indoor Air Handler
Is the indoor blower unit running? If not be sure that the electrical power switch at your furnace or air conditioner air-handler is in the "on" position. Typically the air handler or blower unit is indoors inside the basement, crawl area, or attic.
Also see ELECTRIC MOTOR DIAGNOSTIC GUIDE.
Step 3: Check the Air Conditioning /Heat Pump Air Filter(s)
If your air conditioning equipment is running but little or no cool air is coming out of the supply registers, check that your air filter(s) have not become blocked with dirt and debris.
See A/C Filter Problems for details
Step 4: Check the Air Conditioning /Heat Pump system duct work & air supply registers
In ceilings, walls, or floors, where cool air is supposed to be delivered to various rooms in the building, be sure that the register is in the "open" position (you will be able to see through it into the ductwork) and be sure you haven't blocked the supply registers with a carpet or furniture.
Look for an air filter that has come loose and blown into the ductwork, clogging it.
At left you can see a ceiling air supply register that has leak stains around its opening - further investigation for a condensate leak or roof leak is needed.
Step 5: Check the Air Conditioning /Heat Pump indoor air handler blower fan assembly
If the indoor air handler blower fan itself won't start, see BLOWER FAN OPERATION & TESTING. Check for lost power, a fan motor that wont' start or has tripped a motor reset button or needs a start / run capacitor.
Check for a blower fan that is loose on the motor drive shaft or for a broken or lost blower fan drive belt on pulley-driven blower systems.
Also see ELECTRIC MOTOR DIAGNOSTIC GUIDE for details
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Frequently Asked Questions (FAQs) on How to Diagnose & Fix A Cooling System Air Conditioner or Heat Pump that is Not Working or has Lost Cooling Capacity
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However we have posted FAQs at the remaining articles in this series.
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