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How to Diagnose & Repair Loss of Air Conditioner Cooling Capacity AirCondAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• How to diagnose & repair loss of air conditioning cooling capacity
• Air conditioner compressor defect diagnosis

This chapter of "How to Inspect the Central Air Conditioning or Cooling System" discusses the the diagnosis and correction of lost or reduced air conditioner cooling capacity. Since the 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 problems with any of the three major 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:
LOST COOLING CAPACITY (this article),
OPERATING DEFECTS describing noises, failure to start, and inadequate cool air volume,
COMPRESSOR CONDENSER which describes problems with air conditioner compressor/condenser units,
AIR HANDLER UNIT which describes problems with the air handler, air filters, and the cooling coil itself,
DUCT SYSTEM DEFECTS which describes problems with the duct system.
Also see How to Measure Central Air Conditioning Temperatures for a discussion of what temperatures to expect at different points in the air conditioning system, and see How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

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 links at left.

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

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.

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.

• Clogged 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.
• Damaged cooling 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.
• Cooling Coil Ice-Up 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. For a detailed discussion of air conditioner or other refrigeration (or dehumidifier) cooling coil ice-up diagnosis and cure, see Air Conditioning Cooling Coil or Evaporator Coil Ice-up
• Improper refrigerant charge - too little: 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.
  Watch out for refrigerant leaks that lead to a repeat of this problem. If the 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.
• Improper refrigerant charge - too much can also lead to improper air conditioning system operation and in some cases can damage the 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.
• Loss of most refrigerant from an air conditioning system means that the cooling coil will not get cool at all. 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.
• Compressor problems such as an aging cooling compressor 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.

AIR CONDITIONING SYSTEMS Chapter Index

To continue reading this air conditioning inspection guide, use links to the document chapters at left or below. Links shown in green font indicate where you are in this document.

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