How to Diagnose & Repair Loss of Air Conditioner Cooling Capacity or an Air Conditioner that is Not Working InspectAPedia® -
How to diagnose & repair loss of air conditioning cooling capacity or has stopped working
Air conditioner repair checklist: before calling an air conditioning service technician check these items
Air conditioner compressor defect diagnosis
How to diagnose and fix an air conditioning system that is not working
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This article discusses the
how to diagnose and correct air conditioning problems like lost or reduced air conditioner cooling capacity or an air conditioner that won't start. 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.
What to Check First if the Air Conditioner Output is Inadequate or A/C Won't Run
These Simple Checks May Enable Inexpensive Repair of Lost Cooling Output from an Air Conditioner
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.
Diagnose Air Conditioner Output Cool Air Flow Too Weak, Too Cold, or Too Warm
Air Conditioner Blower fan unit not moving enough air: too little air coming out of your air conditioning ducts?
Check the condition of the blower unit: if it's dirty the blower may be spinning but not moving much air. See DIRTY A/C BLOWERS for details.
Dirty filters or iced coils or crimped or disconnected air ducts can also cause loss of cool air or too little cool air coming out of supply registers.
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 Conditioner Filter Clogging Problems Cause Weak Cool Air Flow
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.
Air Filter problems: not enough air coming out of air conditioning ducts? Check for a very dirty, blocked air filter or blower fan. See AIR FILTERS for HVAC SYSTEMS and AIR HANDLER UNITS
Air Conditioner Compressor Problems - noisy or hard starting air conditioner compressors
Compressor problems - Air Conditioner Compressor: problems such as an aging air conditioner compressor motor that is at or near the end of its life may be unable to
properly compress the returning refrigerant gas to a sufficiently high pressure. A service technician will need to evaluate and test the system
and if needed, replace the compressor.
Since this is a costly repair, be sure to ask why the compressor failed and to correct
any underlying cause (such as low voltage). Variations in line voltage can lead to improper compressor operation and loss of cooling output.
If you have a hard-starting air conditioner compressor that "hums" but doesn't start, it may be possible to get more life out of the compressor motor with a simple starting capacitor (rather than a costly whole new compressor motor.) See and HARD STARTING COMPRESSOR MOTORS and CAPACITORS for HARD STARTING MOTORS.
Cooling Coil Ice-Up on the air conditioner air handler or evaporator coil: A second result of the reduced air flow due to a dirty air conditioning filter can cause
the evaporator coil (the cooling coil) in the
air handler to become blocked by ice, stopping or significantly reducing cool air output from the system.
A visual inspection
of the cooling coil in the air handler can quickly show whether or not it's ice-covered. If the coil is iced-up and blocked,
turn off the cooling system entirely until the ice has all evaporated and cleared. Be sure that your condensate drain is
not blocked and that the water from melting ice will be properly disposed-of.
If you replace all dirty filters on the
system and remove ice from an iced coil and the coil ices up again when the system is turned back on, you may have the next
condition in this list.
Air Conditioning System Dehumidification Problem Diagnosis & Cures
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. What happens is simple:
If an air conditioning compressor unit is oversized (too many BTUH of cooling capacity) what happens is it cools the room so quickly that the system does not move enough total volume of air across the cooling coil to remove much moisture before the room temperature has dropped to the A/C cut-off point.
In other words, an air conditioner needs to run longer, and move more total volume of air through itself to drop room humidity than it does to just cool the air. So "bigger" cooling capacity or higher BTU capacity for an air conditioning system is not necessarily better, and it can actually be a problem.
Key Air Conditioning Inadequate Dehumidification Symptom: If your cooling system is otherwise working normally, and it cools the room temperature quickly but the room humidity stays high, an over-sized unit is likely to be the problem.
Cures for inadequate dehumidification by an air conditioner
First make sure that the equipment is operating properly: is it cooling - check that temperatures are dropping normally when the system is running.
Check that there is not an abnormal moisture source such as leaks into the building or its wall or ceiling cavities from any other source. Check to see if the condensate drain from the air conditioner is producing water. If you see lots of A/C condensate dripping out of the system condensate drain but room humidity is still high, we suspect that there may be an abnormal humidity source. At the end of this list we discuss adding additional dehumidification capacity.
Adjust the A/C unit controls to increase dehumidification: discuss with your HVAC service technician whether there are technical changes that might be made to fan speed or other controls that might improve A/C unit dehumidification. We're doubtful there is much mileage in this but it's worth asking.
Increase the cooling load on the installed air conditioner by making it cool a larger area - like maybe leaving the doors open to other rooms - which we doubt is suitable in most cases. Our photo (above left) shows a wall mounted air handler from a Sanyo™ split system air conditioner that was not adequately dehumidifying the bedroom where it was installed, even though the room was cold enough to hang meat. The occupants experimented with leaving the bedroom door opened, as the rest of their home did not have air conditioning. That proved just enough to cause the system to dehumidify beautifully.
Adjust the building HVAC system ductwork: if a non-dehumidfying central air conditioning system (as opposed to a window unit or a wall-mounted split system unit) is otherwise working well, it may be possible to adjust its load and thus improve its dehumidification by making changes in the duct system, such as increasing the return air to the air handler from additional building areas.
Replace the oversized air conditioner: Unfortunately the most likely fix for an A/C system that is not dehumidifying may be an ugly one - either replace the unit with one that is properly matched to the size of the area to be cooled
Select an A/C unit of the proper size. See AIR CONDITIONER BTU CHART for the data useful to do this. Whoever selected and installed the air conditioning unit needed to relate the room size to the AC capacity. Also see COOLING RULES OF THUMB to guesstimate how many tons or BTUs of cooling a building needs and see RATED COOLING CAPACITY to determine the cooling capacity of existing air conditioning equipment.
Add supplemental dehumidification. For wet conditions that exceed the capacity of the air conditioner itself, or when you require both unusually low temperatures and further dehumidification (such as a seed storage facility described by one of our readers), it may be necessary to add a separate free-standing or portable dehumidifier to the system to reach the temperature and humidity targets you need.
In an area of our forensic laboratory we use a Sears® dehumidifier, model 580.54501 - 50 pint (also available as 580.54701 - 70 Pint Low Temp) (cost about $200.). The Sears portable dehumidifier instruction manual (Part# 3828A20803B) confirms on p.7 that the humidity control can be set anywhere between 35% and 70%. You can also adjust the fan speed (low / high) and also set an on-off cycle period of 3 hrs or 6 hrs.
Operating a dehumidifier (which uses the same technology as an air conditioner) will have a side effect of pumping a little heat into the dehumidified area - the output side of the dehumidifier produces air that is warmer than its input side. Depending on the size of the area being conditioned, that added heat might help compensate for an air conditioner that was a little oversized for the space.
Air Conditioning Air Duct Problems and Cool Air Flow Defects - Poor Air Flow
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.
One client had us drive a considerable distance to repair her apartment's central air conditioning system after having had several unsuccessful service calls.
Apparently
no one had managed to get into a rather tight and hard-to-enter attic crawl space where the cooling ducts were routed.
We found that the main cooling duct had become disconnected.
The attic was nice and cool but no cool air was being blown
into the living area. Check the condition of the duct system for blocked ducts, loose leaky connections, closed dampers,
crimps and bends, before calling your service technician.
See DUCT SYSTEM DEFECTS for details of various A/C duct problems and how to detect and correct them.
Air Conditioner Won't Start - electrical problems
Electrical problems: air conditioning system won't start: it may sound silly, but is the air conditioner turned on?
Has the cooling thermostat been set to "cool" and the temperature set below ambient room temperature?
Do both the outdoor compressor/condenser unit and the indoor blower fan/evaporator coil unit have electrical power?
Has the air conditioning electrical wiring been physically damaged or cut? Photo courtesy of Tim Hemm.
Are the power switches on at these units, are the fuses good, are the circuit breakers in the "on" position, and is the thermostat set correctly? See CONTROLS & SWITCHES and THERMOSTATS for some diagnostic tips.
Air Conditioner Won't Start or Stays Off Due to Condensate Pan Switch
Condensate pan switch lockout: an attic or other air conditioner air handler condensate drip tray or drip pan located under an air handler is installed to catch air handler condensate leaks if the normal condensate drain system fails. Some condensate pans have their own separate overflow drain (a proper installation) or share their drain with the normal condensate drain (an improper installation).
But on some air conditioning air handlers the installer may provide a condensate overflow pan switch rather than a separate pan drain line. In this installation the switch is designed to turn off the air conditioning system if it finds condensate water in the overflow pan. The idea is to shut down the air conditioner before there is a more costly leak into the building insulation or ceiling.
Refrigerant problems: Improper air conditioner refrigerant charge - too little, too much, too leaky: an air conditioner system which has lost some (but not most) of its refrigerant
will sometimes run too cold at the evaporator coil, leading to coil icing and loss of cool air delivery in the home.
If the filters are
clean and the coil ices-up this condition may be present. A service technician will need to evaluate and test the system and if needed,
adjust the refrigerant charge.
Low refrigerant level in the air conditioning system: Watch out for refrigerant leaks that lead to a repeat of this problem. An air conditioner or refrigerator is a sealed system that should not normally "use up" refrigerant. If the cooling system is
low on refrigerant because it has a leak, it is much smarter to find and fix the leak than to simply keep adding refrigerant. If you
keep adding refrigerant to a cooling system you're leaking possible contaminants into the environment as well as wasting money.
Abnormally low output air temperature: A refrigerant leak in an air conditioning system may show up first as abnormally low system output air temperature, followed by rising air temperatures, followed by just plain old warm air coming out of the system, as the amount of refrigerant that has been lost increases.
Loss of most refrigerant from an air conditioning system means that the cooling coil will not get cool at all.
Abnormally high output air temperature: A service technician will need to evaluate and test the system and if needed,
find and fix the refrigerant leak, evacuate the system, and install the proper refrigerant charge. See A/C REFRIGERANT LEAK DETECTION for diagnostic details.
Don't keep adding refrigerant. Refrigerant leaks should be found and repaired. It may be easier to keep adding refrigerant, and sometimes a refrigerant leak can be hard to find, but a proper repair is to find an fix the refrigerant leak, not just to keep adding refrigerant. See REFRIGERANT LEAK DETECTION. See A/C REFRIGERANT LEAK DETECTION for details.
Improper refrigerant charge - too much can also lead to improper air conditioning system operation and in
some cases can damage the compressor (called liquid-slugging the air conditioner compressor). A service technician will need to evaluate and test the system and if needed,
adjust the refrigerant charge. In this case the cooling coil is probably not going to ice-over, it just won't get cool.
Air Conditioner Won't Start - Blower Fan Will Not Turn on or Will Not Turn Off
Thermostat problems: Air Conditioner Thermostats:
Air conditioner won't turn on, or fan won't turn on or won't turn off.
See THERMOSTATS for a discussion of how air conditioner thermostats work and how the air conditioner blower fan controls work.
Air Conditioner Air Handler Blower motor Won't Start?
See MOTOR OVERLOAD RESET SWITCH just to be sure that the air handler blower fan motor has not shut off on thermal overload. And if your blower fan is driven by a fan belt and an electric motor, of course check to see that the drive belt is in place and un-damaged. If the blower fan belt is broken the electric motor will run just fine (you may be able to hear it) but the blower fan assembly itself won't be turning.
Air Conditioner Compressor Diagnosis: How to Diagnose & Repair an Air Conditioner Compressor Which has Lost Cooling Capacity
A compressor which appears to have lost cooling capacity can be diagnosed by a service technician who can connect the appropriate test
gauges to the system. Lower than normal discharge pressure and higher than normal suction vacuum will indicate this problem.
But before assuming that something is wrong with the air conditioning compressor, some basic investigation is in order.
Unless there is an obvious indication of a compressor problem (noise, hard starting, compressor
won't start), the service technician, to be thorough and economical, will inspect the system in an order, checking the easy and least-costly
problems first, such as presence of electrical power, proper setting and operation of system controls, condition of filters, condition of duct work, operation
of blower fans, before moving on to check the compressor itself by looking at the air conditioner operating temperatures, pressures, and
current draw in Amps.
Cooling Capacity of the Air Conditioning Equipment
The cooling capacity of an air conditioning equipment refers to the ability of the compressor/condenser (usually outside) and the air handler/evaporator (usually inside)
to deliver cool air to the occupied space.
Briefly,
the compressor/condenser draws refrigerant gas from the building air handler, compresses it
and cools it back to a liquid refrigerant, and the air handler/evaporator coil permits liquid refrigerant
to evaporate inside a cooling coil, across which the fan blows building air to cool and dehumidify it.
The particular
combination of this equipment has a cooling capacity, usually rated in BTUh or thousands of BTU's of cooling capacity per hour,
documented on equipment data tags discussed above at "RATED COOLING CAPACITY" - see AIR CONDITIONER BTU CHART and see COOLING RULES OF THUMB to guesstimate how many tons or BTUs of cooling a building needs and see RATED COOLING CAPACITY to determine the cooling capacity of existing air conditioning equipment.
Air Conditioner Long "on" cycle and Insufficient Cooling - Loose or Worn Compressors
A longer than normal "on" cycle combined with little or no cool air conditioner output could be due to an inefficient
air conditioning compressor or one which has lost its ability to "compress" the refrigerant due to internal wear.
This condition can be diagnosed by an air conditioning service technician who will install air conditioning
manifold gauges onto the system to check the compressor suction vacuum and discharge or "high side" output
pressure. If gauge ports are not installed on the air conditioner compressor unit the technician cannot
make this test without cutting the refrigerant lines to install gauge ports (adding to the cost of this diagnosis).
Low air conditioner motor amperage draw
Low amperage draw: unlike a high-amp current draw which indicates that the compressor is danged internally in a way that its
piston(s) is(are) tight in the cylinder, a low-amp current draw, if below normal, may confirm internal wear on
the compressor parts, and would support the diagnosis that the compressor is worn and inefficient. Where there are no gauge
ports to actually measure compressor low side and high side vacuum and pressure, this simple electrical test is a useful
first step.
Abnormal air conditioner compressor pressure readings
Refrigerant line pressure readings which are abnormal (probably too low) on the high pressure side (compressor output) or
on the low pressure side (compressor input or suction line) can indicate a problem with the compressor's ability to
develop normal operating pressure ranges and thus will affect the cooling capacity of the air conditioning system.
For more details on air conditioner refrigerant line pressures and how they are examined see COMPRESSOR PRESSURE READINGS
Details about air conditioning compressor functions, how air conditioner compressors work, what goes wrong with air conditioner compressors, and how to measure and diagnose air conditioner compressors are provided at COMPRESSOR CONDENSER.
Cooling Capacity of the Air Conditioning Duct 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 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.
How to diagnose and fix an air conditioning system that is not working
If your air conditioning system won't work, follow our diagnostic guides
At LOST COOLING CAPACITY, our focus is on the case in which the air conditioning system seems to be "running" but not enough cool air, or no cool air at all is being delivered to the occupied space. Sketch from Carson Dunlop.
At OPERATING DEFECTS we take you through the major air conditioning problem symptoms and how to get the air conditioning system working again.
At CONTROLS & SWITCHES we explain the many electrical switches and controls that control an air conditioner or heat pump system. You'll need to check these if your air conditioner won't start.
See our complete list of air conditioning system diagnostic and repair guide articles just below.
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 SYSTEMS.
If your air conditioning system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Timothy Hemm, Yucala, CA, contributed photographs of electrical wiring and equipment installed in California buildings. Mr. Hemm can be contacted at TimHemm@yahoo.com
Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. 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. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
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 volume
A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair - a detailed air conditioning system diagnostic checklist
Thanks to reader and research scientist Cyril Roberts, Barbados, for technical discussion and investigation of air conditioning system dehumidification problems (April 2009).
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend)
Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
More Information on Building Diagnostic Inspections and Repairs
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