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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
Diagnosis of inadequate dehumidification in buildings:
Tthis article discusses the causes of inadequate indoor air dehumidification when you are running a central air conditioner or heat pump system. If your central air conditioning system cools the building air but the indoor humidity remains too high, the system may be over-sized, as we explain here.
We also consider other sources of excessive water in central air systems, air handlers, and ductwork.
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Air Conditioning Dehumidification Problems: air conditioning system cools but does not dehumidify the room.
The most common cause of inadequate dehumidification by an air conditioning system is the installation of a cooling unit which has too much capacity, or is "over-sized" for the space it is being used to cool.
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What happens is simple:
Cures for inadequate dehumidification by an air conditioner
See LOST COOLING CAPACITY 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. We provide links to other air conditioning system diagnostic articles too.
Troubleshooting High Indoor Humidity Levels
Reader Question: 11/30/2014 Glen de Valk said:
Last May we replaced our central air unit in our 2400 sq.ft. home in Sarasota, FL. It was replaced with the same size unit that had been in place for over 20 years (3.5 tons) and cooled and dehumidified very well. However, the new unit does not dehumidify the air regardless where temp. is set and keeps the humidity level no lower than 60% and as high as 72% when we raise the thermostat to our comfort level around 75 degrees.
We had an independent inspection of the system done and detected that the air humidity at the registers was 83-85% when the unit was running; when the compressor shuts off and the fan runs for a pre-set 90 seconds more, the humidity level goes to 100%.
The installer cancelled the 90 second period of running but the humidity level still stays at 82-85% coming out of the registers and around 60 to 65 % at the returns. The house was also thoroughly tested for plumbing leaks, etc. and there are none.
The A/C contractor thought the 3.5 ton unit was too big and replaced it with a 3 ton unit so it would run longer cycles. That made absolutely no difference in dehumidification. The contractor seems to be at a loss to cure it. Please advise. Thanks.
Glen, usually when an air conditioner is not adequately dehumidifying the indoor air it is because its cooling capacity is too great - the air cools and shuts off the cooling system before the humidity has dropped.
Research on Reducing Indoor Humidity Levels
Continue reading at AIR CONDITIONER BTU CHART - where we discuss the air conditioning system sizing problem or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
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Question: Is there a Way to Scale Down Oversized Air Conditioner Units?
Some years ago now, I had 2 ACs installed in my home. It cost me about $10k and now I am told they “overinstalled” with 7 tons of cooling when I needed 4.5 tons. Problems keep coming, of course and the only fix I hear is to install new ones with less tonnage. Seems to me, there ought to be some way to scale down the ones I have to fit my home. Utility cost is out of sight, of course. I am told the savings to reduce the AC capacity would be significant. Is there some way I can scale down the volume of the units I have? Seems like a better fix for me. What say you? - W.S.
Reply: We are doubtful that you can squeeze down an oversized A/C system
A competent onsite inspection by an expert, especially if you employ an experienced HVAC designer or engineer usually finds additional clues that help accurately diagnose a problem. That said, here are some things to consider:
Question: Why is our Air Conditioner Rusting on the Inside?
We have lived in our new home for 1 year and 7 months. Our air conditioner is rusting on the inside. The blower fan and all the internal areas are rusting. We have blown insulation in the attic and exterior walls. Living area is 2400 sq ft and we have a 2 speed, 3 ton Lennox AC unit.
The Lennox inspector looked at the whole set up and said it was a moisture problem. That's hard to believe that that is the problem. We had a manual J load done on our home to determine the size of the AC before it was installed. We have followed everything that we were told to do. 2 different electrical components have failed due to rust. The AC guys said they have 3 more units rusting the same exact way. 2 are in closets in the home and one is in an attic with regular fiberglass insulation. All 4 units are Lennox 2 speed units.
What could possibly be our problem? Does Lennox have a problem that their not sharing with us? Any help would be appreciated! We don't know what to do next. - R. & C. R. - South Louisiana
Reply: Check your A/C BTU Rating and Sizing Specs
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem. That said, and we are just guessing, as we have so little information, but
Question: can water in the air conditioner/heat pump condensate drip pan or on the cooling coil cause high indoor humidity in the building?
The short answer is no. The cooling coil is removing humidity from air passing over it, not adding humidity to it. Edgardo, a reader, questioned whether or not running the blower fan in the air handler full time would increase building humidity by picking up residual moisture from an otherwise properly working cooling coil and condensate drip pan when the cooling system is off.
Our opinion is that the volume of water remaining on a wet cooling coil or condensate drip pan (one that is draining, not keeping a reservoir of water in the system) is negligible and very unlikely to explain high indoor humidity when the A/C is off. Details of this discussion are found at Questions & Answers about whether or not to run the heating or air conditioning blower fan continuously which is found within the article titled BLOWER FAN CONTINUOUS OPERATION
If your air conditioning system won't work, follow our diagnostic guides
See our complete list of air conditioning system diagnostic and repair guide articles just below.
Sketch courtesy of Carson Dunlop Associates..
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 & HEAT PUMP SYSTEMS.
If your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.
Questions & answers or comments about how to diagnose and cure inadequate building dehumidification - excessive indoor humidity levels.
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