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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
FAN NOISES, HVAC
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
How to diagnose weak or too-warm air flow from an air conditioning or heat pump system. 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 temperature, or an air conditioner that won't start.
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WEAK AIR FLOW: is the air conditioner (or when heating, the heating system) blower fan unit not moving enough air, so that there is too little air coming out of your air supply registers? Here is a list of things to check, in the best order.
[Click to enlarge any image]
1. Check that the air register is open
2. Check for a dirty or clogged air filter: replace the filter.
Watch out: some HVAC systems have more than one air filter in more than one location. Be sure you've found all of them. For example a filter may be located at a central return air inlet grille and another may be located at the air handler itself.
Clogged Air Conditioner filters can lead to lost cooling capacity first, because the clogged filter reduces the air flow
through the system, meaning that you'll feel less air flow at the supply registers than was previously present.
3. Check for a dirty or broken blower fan: if the squirrel cage fan in the blower unit is dirty the blower may be spinning but not moving much air. If the blower is a belt-driven unit check that the belt is intact and that the blower spins.
See DIRTY A/C BLOWERS for details.
If you don't know what an "air handler" or blower unit is, or for more blower unit diagnostics see and AIR HANDLER / BLOWER UNITS
4. Check for an iced cooling coil inside the air handler; a refrigerant leak can cause frosting while later the when more refrigerant has been lost the result is delivery of inadequately-cooled air.
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.
5. Check the ductwork for crimps, leaks, disconnects: crimped or disconnected air ducts can also cause loss of cool air or too little cool air coming out of supply registers.
Other HVAC Air Delivery Problems: no air flow, air flow too warm, air too humid
Check all of the heating and cooling controls to be sure that they are set properly and working normally. The thermostat is set to COOL, FAN to AUTO or ON, HEAT to OFF, and the set temperature on the thermostat is set below room temperature (if you want cooling).
SNAFUs in the individual controls and relays and switches for the air handler, blower, compressor/condenser unit and refrigerant metering equipment will, if not working properly, lead to these same complaints.
Check the following causes of complete loss of air flow
AIR TOO WARM: Or is there air blowing out of the supply registers but it's not cool enough?
Typical causes of too-warm air flow out of an HVAC system in cooling mode are
AIR TOO HUMID: if the air conditioning system is not dehumidifying, and presuming no one has left windows or doors open to humid outdoor air, air flow may be too rapid or the system may be over-sized. See DEHUMIDIFICATION PROBLEMS
HVAC Control SNAFUs That Can Lead to Too-Warm Air Conditioning or Weak Air Flow
As you read below, a reader (Pete) reminded us that even when the A/C system seems to be working properly a too-warm air output problem in a heat pump system could be due to emergency or backup-heat being left in the "ON" position.
Question: why is my heat pump blowing warm air?
4/30/2014 Pete said:
I have an old unit that will not blow cool/cold air. I have had a tech out twice and I am trying to see if there are any things that I can check or ask my technician to check. The tech had the unit working properly, after his last visit, until about 2 weeks ago. At that time we had a cold-snap and I had to turn my heat back on. When I turned it back to AC it has not worked properly since.
The outside unit (condenser) is running as is the air handler. Plenty of air is blowing out of the registers but it is only about 70-71 degrees. I do not know anything about fixing ACs but I am pretty handy and I have been researching on the web.
Some of the viable options I found are a stuck or bad Reversing Valve, coolant line could be blocked or contaminated or the Thermostatic Expansion Valve could be bad. Does that sound right? Any thoughts? Also, I noticed that the high pressure line (small copper tubing, I think) coming out of the outside condenser is cold to the touch. Should that not be warm/hot? I really would like to get one more season out of the unit. PS: all filters are clean.
With the benefit of hind-sight - your comments below, that cold refrigerant line was an important clue.
Reader follow-up: (2 hours later) Problem solved: emergency heat stuck on
Found problem. AC was working but the emergency heat strips were stuck on. So the cold air was getting heated. Replaced and is working. Hooray!
Check and Fix These Existing Air Conditioning Problems Before Trying to Improve its Cooling Capacity
Watch out: It could be a mistake to spend on any costly air conditioning improvement if the original system actually already had the needed capacity, but simply needed maintenance (like replacing a filter - A/C Filter Problems) or repair (like repairing a leaky duct - A/C Air Duct Problems).
FIRST: review all of the air conditioning performance diagnosis suggestions here to be sure there is not something that needs to be repaired or corrected with the system.
For example we have seen cool air output significantly improved by finding and fixing a disconnected cool air duct that no one had noticed in a hard-to-access crawl area.
Certainly some central air conditioning systems, especially retrofit designs, have less than optimum duct design, such as inadequate central return air registers, room doors that are so tight that it is difficult to blow cool air into the room when the door is closed, inadequate supply ducts or less than optimum supply register placement such as only in floors.
But redesigning and installing for an optimum air conditioning duct system can be costly, so it might be worth taking some other steps.
SECOND: make sure that other energy-savings steps have been taken in the building, such as proper insulation, sealing un-wanted drafts, etc. See ENERGY SAVINGS in buildings - those suggestions apply to both heating and cooling costs.
If your HVAC service technician is sure that the present cooling system is working as intended, then if you are not considering supply or return air duct improvements, or a replacement air conditioner system of higher capacity, you might consider a stronger blower fan (discuss what you could do with your HVAC tech), or booster fans individual registers.
Watch out - just boosting air conditioner air flow by installing a higher capacity blower fan is not that simple - if the blower moves air through the duct system faster than the design speed for the system ,the cooling coil may be insufficient in capacity, the air will not be dehumidified (and the building will be less comfortable - A/C Not Dehumidifying), or you might get annoying duct or equipment noises. Discuss these possibilities with your HVAC service company.
Continue reading at DUCT & AIR FLOW PROBLEMS
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
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
See SHORT CYCLING AC COMPRESSOR for details of diagnosing and repairing an AC unit that keeps cycling on and off
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 condenser just put in. Help. - Ginny 5/17/12
Question: AC blowing just jot air
(June 18, 2014) Ellie said: Our a/c was blowing only hot air. Call repairman and he installed wires above the fan running along what looks like a large conduit pipe with a large loop of wire sticking out above the grill. We have a Carrier Heat Pump w/ a/c and have had a lot of vibration problems and at least one annual repair. We've replaced the compressor once.
This repair looks dangerous and we're selling the house and worry this repair might not pass the home inspection. Is it common to rewire the a/c "board" out of the compressor cover? We don't think the kid they sent out and the more experienced man who came later made a proper repair. Seems like the wires should be inside where the original wires were. We live in the mountains and there is a lot of wildlife that cause mischief. We worry an exposed wire like this would be a serious temptation. Is this kind of wiring "normal."
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:
Ellie , no, not common and potentially dangerous. This should not be a big cost to put the components where they belong.
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?
Question: poor air circulation & poor air temperature at my HVAC system
(Feb 16, 2014) Stephanie said:
Hello! Looking at a foreclosure property and the inspection today revealed a problem with the HVAC system. The home is 2.5 levels and includes a basement. The 2nd level (master with 2 BRs) does not have a thermostat, and also has poor air circulation- temperature is controlled via thermostat on loft/3rd level . The inspector mentioned a 'temperate change' from vent to BR space on 2nd floor. There was no noticeable heat coming from vents on 2nd level, but noticeable heat coming from loft level. Any ideas on what is going on?? Also as an FYI- first level has 2 different thermostat/zone controls and basement has one. Are 4 furnaces total. Thanks for any help, I'm a complete novice when it comes to this stuff!
Stephanie, from just your message I can't guess at whether the problem is with
The fact that you observe plenty of heat coming from the loft level tells us that the basic heating equipment is working and suggests focusing on a duct or register problem.
I'm glad to address your questions here, but it'd be more useful to post heating questions on an appropriate heating diagnosis page where other readers may also have something to offer.
If you search InspectApedia for
no heat - furnace
you'll see our lead article on how we approach diagnosing the problem
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