Or for more detailed troubleshooting and procedures used by trained HVAC repair technicians, can see our list of detailed diagnosis and repair procedures given below.
The air conditioning system operates, both indoor blower and outdoor compressor are running, but the does not produce cool air, or not enough cool air:
see
Dirty air conditioning filters, - a source of increased operating costs. Very dirty filters can eventually block the fan itself, leading to more costly repairs.
The filters should be changed monthly when the system is in use. Failure to properly filter dust from the return air supply can load the fan or evaporator coil with dust and prevent proper system operation. Installing a filter is normally a minor expense.
Dirty, blocked evaporator coils can result in improper system operation, very low output temperatures, low air flow (compensated sometimes by increased fan speed), and sometimes frost on the coil and failure of system components.
AIR FILTERS for HVAC SYSTEMS - air filters are critical not only for building health and comfort but to keep an adequate air volume moving through the air conditioning or heat pump system
SOURCES FOR AIR FILTERS - where to obtain air filters of various sorts, how effective are other air cleaners such as free-standing air purifier units? Are some of them dangerous? Maybe. Are claims exaggerated? Usually.
Legionella BACTERIA & HVAC EQUIPMENT how to remove or prevent bacterial growth in air conditioning systems, cleaning condensate trays, cooling towers, use of chlorine, bromine, disinfectants in air conditioners
Air Handler Unit
Inside cooling or evaporator coil defects
that can be seen by eye: dirty coil, blocked coil, frost on the coil, improperly sized evaporator coil, improper evaporator or cooling coil placement in the system.
Air flow across the air conditioning evaporator coil:
if airflow is weak for any reason (dirty coil, duct system defects, blower fan defects, dirty
blower squirrel cage fan), the air conditioning system will not operate properly.
Some experts write that there should be between 350 and 400 cubic feet of air per minute (CFM) moving across the evaporator (cooling) coil for each ton of air conditioner capacity.
One ton = 12,000 BTUH so if your AC unit is a 24,000 BTUH unit it is a "two ton" unit and needs to see 700 to 800 CFM of air across the evaporator coil.
Some home inspectors and air conditioning service technicians carry a small airflow meter that can actually measure this number with fair accuracy.
The same tool is nice for comparing air flow and balancing air flow at various building supply ducts and registers.
often requires cutting refrigerant lines, removal of the coil and other components for cleaning, and reinstallation, pulling a vacuum on the refrigerant lines, and recharge with refrigerant. Such service and repair may involve significant expense, although there are some "in place" cleaning methods using foams and sprays that are a simpler procedure.
COMPRESSOR / CONDENSER REPAIR - home - problems with air conditioner compressor/condenser units - us this link to find our full list of HVAC condenser/compressor diagnostic & repair articles.
Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week.
Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control and some refrigeration class instructions opine that 80% of problems on these systems are electrical in nature.
So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
SAFETY CONTROLS what safety controls and switches are required on air conditioners?
Cooling / Evaporator Coil
COOLING COIL or EVAPORATOR COIL - problems at the evaporator coil can cause total loss of cooling capacity (or heating with a heat pump)
The air conditioner fuse keeps blowing or the circuit breaker trips: could mean a compressor which needs repair or replacement, or it could mean a problem with the unit's electrical wiring, such as use of aluminum wiring combined with bad electrical connections.
Have your service technician check the condition of the electrical circuit first (that's cheaper than a new air conditioning compressor) and then check the condition of the compressor.
ELECTRIC MOTOR DIAGNOSTIC GUIDE - diagnostic procedures for electric motors used on oil burners, air handler blower assemblies and fans, air conditioners, heat pumps, well pumps, etc.
BACKUP HEAT for HEAT PUMPS - types of backup heat, diagnosing back up heat pump heat not working properly, types of backup heat; problems with backup heat; begin here if your heat pump is not providing enough heat or if your air conditioning system provides heat when it should be providing cooling
HEAT PUMPS - home - includes heat pump terms, definitions & terminology, diagnosis & repair articles specifically for heat pumps
HEAT PUMPS, GROUNDWATER - what are the COP's and EER's of groundwater based heat pump systems?
AIR CONDITIONER TEMPERATURES - what are the normal input and output temperatures and air temperatures & where are the measured?
LOST COOLING CAPACITY - what to do when not enough cool air comes out of the system - use this link to see our key diagnostic articles if your A/C unit is not cooling or the air flow is too weak.
OPERATING DEFECTS - major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volumes
The air conditioning system will not operate at all: power may be off, controls may be improperly set, or the system may be inoperative. (Confirm that the system has electrical power and that all of its control switches and thermostat are set to on and cooling positions.
The compressor squealed at startup, indicating that service may be needed promptly to prevent possibly costly damage to the system. This repair/maintenance item should not be deferred.
I have a outside heat pump unit and the heat works , but when I turn on A/C the compressor doesn’t come on. The plug to compressor was unplugged so I plugged it in and unit sounded like it shorted out. Any thoughts - On 2020-07-25 by Brandon -
Rely by (mod)
That sounds to me as if a relay or control board has shorted out or worse, a short circuit occurred in the compressor motor itself.
Musty odor from the air conditioner
A musty smell when unit comes on - On 2019-10-03
by Anonymous -
Rely
by (mod)
Anon: check for mold and water in the air handler supply and return plenums and in the ductwork.
HVAC Unit Control board has no power out - bad transformer?
My control board has power going to transformer but no power out. Is it a bad transformer? - On 2019-07-19 by Rick
Reply by (mod) -
It certainly could be a bad Transformer, or something as simple as a loose or broken connector. I would check all the connectors in and out before replacing the parts.
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In addition to any citations in the article above, a full list is available on request.
Timothy Hemm, Yucala, CA, contributed photographs of electrical wiring and equipment installed in California buildings. Mr. Hemm can be contacted at TimHemm@yahoo.com
In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.