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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
Diagnose & cure HVAC duct problems like weak air flow, leaks, noises, condensation: 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.
This article forms part 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.
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Duct problems: Damaged Air Conditioning Ducts such as ducts which have been improperly routed and are crimped, crushed, or have
excessive bends can reduce cool air flow in an otherwise properly functioning system.
Even if a very high BTUH capacity cooling system is installed, if the duct system is defective the ability of the system to deliver cool air to the occupied space can be severely or even totally lost.
Duct System Efficiency (in percent) describes the percent of cooled air produced by the A/C equipment which is actually delivered to the occupied space. This number is less than 100% because of air flow restrictions and losses in the duct work.
Duct Delivery Effectiveness is the percent of cooling capacity which is delivered through the registers into the occupied space. Registers themselves restrict air flow. See DUCT SYSTEM & DUCT DEFECTS - see links at left.
Cooling Capacity of the Whole Air Conditioning System
So the ability of the entire A/C system to cool a building or rooms in it requires that both the cooling equipment and the duct system be in proper working order.
Details about duct system and air handler diagnosis, including duct defects, air filter defects, and air handler problems are provided at AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself.
If you don't see information you want, ask us for it using the comments box on this page. 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.
Other Causes of Weak A/C or Heat Airflow Blamed Misdiagnosed as a Duct System Defect
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
Ceiling Stains due to Condensation or Ice Leaks
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.
Accidental airflow through an idle ceiling duct system in winter can cause accumulation of condensation and ice.
Poor or missing insulation on an attic duct system can also cause excessive in-duct condensation and leaks such as the stain shown here.
Air Conditioner Blower fan unit not moving enough air: too little air coming out of your air conditioning ducts?
Air flow that is too slow for any reason (such as a dirty filter or dirty blower fan assembly blades) can cause first, air temperatures that are abnormally low coming out of the air conditioner, and eventually a reduction in air flow as coil ices over. See A/C Cooling Coil Icing.
Air flow that is too fast for any reason (improper fan motor, speed, fan belt or pulley size, duct design, duct registers removed, etc) can produce air that is not cool enough and can prevent proper air dehumidification (oversized A/C system). A/C Not Dehumidifying.
Several causes of cooling or evaporator coil icing all have the same effect: ice blocks air flow across the coil, resulting in weak air delivery during the cooling season.
Green link shows where you are in this article series.
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
Question: My Air Conditioner won't turn off - what to do?
Carla said: My outside air unit will not turn off on its own. I have to manually turn the breaker off to turn it off. Does anyone know why or how I can fix it?
Carla if your A/C won't turn off it could be that the thermostat is set to a temperature that the system cannot reach - due to lost cooling or due to a setting below the capability of the system. If your A/C won't turn off even if you set the thermostat to a temperature that is above the current room temp, then the thermostat or an A/C control board or switch is bad and needs replacement - in that case you need a service call from a trained HVAC Technician. See OPERATING TEMPERATURES HVAC and also CONTROLS & SWITCHES, A/C - HEAT PUMP
Question: My Air Conditioner (or heat pump) keeps cycling on and off too rapidly - what might be wrong? short A/C on-cycle problems
Joe said: short cycling air conditioner compressor diagnosis: I have the same problem as Mathew: my A/C compressor cycles on and of every ~10 seconds. I is about 5yr old. What can we do to fix this system. Please help. Thanks!
Matthew said: short cycling air conditioner problems: Our air conditioning compressor cycles on and of every few seconds or minutes. What can we do to fix this systems not even a year old
Five causes of a home air conditioner compressor short cycling on and off too rapidly - Short Cycling Air Conditioner Diagnosis & Repair
DanJoeFriedman (mod) said to Joe and Matthew (re questions just above):
In sum, you need a service call from a professional to correctly diagnose and repair the problem. Ask the service tech what she/he found and let us know - what you find will help other readers.
If your air conditioner or heat pump has the opposite problem, staying on too long, see LONG-ON CYCLING AC COMPRESSOR.
Question: Why is my A/C not producing enough cool air?
A/C not producing enough cool air - I had my air conditioning system gassed up last week - $210. ! The unit is not producing enough cold air. The unit is set on 72 and does great at nights but during the day where the temp. outside is reaching mid 90"s it's getting up to 80 in the house. Is my duct work screwed up? How do you repair trailer metal ducting? - Amanda
90 degrees outside and 83 inside with thermometer at 76. Cools off to 76 when sun starts to go down and house then gets cold. New capacitor and condensor just put in. Help. - Ginny 5/17/12
Amanda: if your system is not cooling there could be any of a number of problems - see the article above as a place to start. If your basic complaint is that the A/C temperature at the supply registers is cool enough but the volume of air flow is too weak, we'd start by:
Weak air conditioner air flow - is there a relationship between refrigerant charge level and weak cool air flow rate?
Les said: Weak air conditioner air flow: Our A/C was serviced two months ago and the repairman said it had a leak. $400 later it was recharged with coolant and now the ac is doing the same thing. Very little pressure coming out of vents and no cold air coming out. Does anyone know what I can do for the weekend? It is stifling!!!! See A/C Air Duct Problems
DanJoeFriedman (mod) said:
Les: A leak that was fixed by a re-charge is not as good a repair as a leak that was fixed by finding and fixing the leak - you'll just have to keep adding refrigerant.
But weak air flow out of the vents would not be due to a refrigerant leak; more likely a clogged filter or crushed or disconnected ductwork, or a blower fan problem.
Weak air Flow traced to Clogged Air Filters: Can Clogged Air Filters Affect the Room Thermostat?
(May 13, 2011) Jim said: If air conditioner filters are clogged will it cause the thermostat to shut off?
Jim: clogged A/C filters won't cause a room thermostat to shut off. The thermostat responds to room temperature. However clogged A/C filters that reduce air flow, cause coil frosting, or otherwise reduce or stop the flow of cool air into the room where the thermostat is located would mean that the thermostat would remain "un-satisfied" and should mean that the thermostat says "on" - continuing to call for cooling. See AIR FILTERS for HVAC SYSTEMS
Air Filters & Cooling System Amperage Draw: Could Removing the Air Filters Cause the Electric Motor in the Air Handler to Draw Higher Amps?
Question: got one for you. i put an ammeter on my air handler and it read 8.25 amps, I removed the filters and it went up to 9.75 lmao at the situation the amperage should have gone down. what gives here
Reply: causes of variations in electric motor efficiency and current draw measured in amps
Lost: this amps variation is beyond my expertise, but in general reducing the load on an electric motor will show up as lower amps or current draw, not higher amps. Here are two interesting explanations of amps or current variations on an electric motor that I found when researching the question:
2. Load variations and electric motor efficiency: A second possible source of seeing higher amps or current draw on your blower motor when you pulled out the air filters and thus reduced the load on the blower motor might be illuminated by this U.S. DOE pamphlet "Determining Electric Motor Load and Efficiency" - Quoting: "Most electric motors are designed to run at 50% to 100% of rated load. Maximum efficiency is usually near 75% of rated load. Thus, a 10-horsepower (hp) motor has an acceptable load range of 5 to 10 hp; peak efficiency is at 7.5 hp. A motor’s efficiency tends to decrease dramatically below about 50% load."
Question: what causes warm suction lines in an air conditioner or heat pump system? Warm A/C suction line (should be cold) and zone control dampers that stopped working
JMONTE said: warm A/C suction line question: After my condenser is turned on for about 4 minutes the suction line starts to get warm to the touch. can you tell me what the problem may be
JMONTE: If the HVAC suction line gets warm, you may be out of refrigerant, or the system may be running in heating mode if it's a heat pump. See OPERATING TEMPERATURES HVAC.
Becky, If a motorized HVAC zone control damper is not opening or closing, most likely the motor has failed, or the thermostat that operates that zone control is off or set in an incorrect position. See ZONE DAMPER CONTROLS
Becky said: motorized air conditioning zone dampers not working
My house has "zone" control with dampeners to close off the upstairs over the garage room unless that thermostat is on - the room is not cooling. I have located the damper under the house. What are some causes for the damper not opening and how to repair them? condensation, motor to damper? silicon glued properly?
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