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Air Conditioning Troubleshooting

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High Performance HVAC:  Air Conditioner Troubleshooting

To properly troubleshooting air conditioners one needs to understand some basics of air conditioners including refrigeration, electricity, electrical components and how electro-mechanical controls work, and basic air conditioner components. Before troubleshooting air conditioners you need to identify the basic problem of the air conditioner. Is a component not working and why is the component not working. For example, is the compressor working and if the compressor is not working is it the compressor that is bad or is it an electro-mechanical component that controls the compressor with the problem that will prevent the air conditioner from running? So in the process of troubleshooting air conditioning not only do you need to know the basics of air conditioners you also need to understand basic techniques for troubleshooting air conditioners.

Air Conditioner Types

There are two basic types of air conditioners. The package system air conditioner where all the components for the air conditioner are in one unit or package and there is a split system air conditioner where some of the components are split from each other but connected via wiring and a refrigeration line set. Both systems have basically the same air conditioner components but these components have different configurations. Finding the problem with the air conditioner will require understanding these basic components whether they are configured in a split system air conditioner or a package unit air conditioner.

Air Conditioner Components

The Evaporator

The Evaporator coil is a one of the major components and depending on the problem which needs air conditioner troubleshooting depends on the necessity to check the evaporator coil in the air conditioner. The air conditioner evaporator coil receives low pressure low temperature refrigerant. As refrigerant passes through the evaporator coils it absorbs heat from the air that passes over the coils. In air conditioner troubleshooting it is important to check that the evaporator coil has the proper amount of designed air flow across the coils. It is also important the proper amount of refrigerant is available inside the evaporator coils. The air conditioner system can be overcharged and too much refrigerant will be in the coils or the air conditioner system can be undercharged (possible refrigerant leak) and not have enough refrigerant. In either case, if you are looking for the problem with an air conditioner you will need to have the skills and the tools to know what a proper charge is for an air conditioner system. With airflow across the evaporator coil in air conditioner troubleshooting you need to check the filter to make sure it is not clogged with dirt or debris. Make sure the blower is turning the proper RPM’s so that it pulls (or pushes) the proper amount of airflow across the evaporator coil. Too many supply vents closed off can cause air flow problems. It is important that evaporator coil has the proper amount of airflow across the coil to ensure the air conditioner is working properly. In finding problems with air conditioners this is an essential check of the air conditioner system. Make sure the airflow is good across the evaporator coil when looking for air conditioner problems.

Air Conditioner Components

The Condenser

The condenser coil receives high pressure high temperature refrigerant from the compressor. The compressor and the condenser can be integral to the condensing unit in a split system. Whether it is a split system air conditioner or a package unit air conditioner the compressor and the condenser coil are important components in an air conditioner system. The refrigerant gas travels from the evaporator coil to the compressor where it is changed from a low temperature low pressure refrigerant gas to high pressure high temperature gas. In troubleshooting air conditioners there is not much the layman can do to check the compressor without the proper tools. A basic air conditioner troubleshooting practice for a compressor is to check the wiring. Of course when checking any electrical components in any type of machinery or mechanical equipment is to disconnect or turn off the power to the equipment. In some cases the when an air conditioner fails the wires on the compressor could be burned off. In an troubleshooting especially air conditioning troubleshooting wires can be burned off because of a loose connection or corrosion. Corrosion can cause a loose connection. It is important any loose connections and corrosion be cleaned and terminated properly to the compressor terminals. Since nearly all residential and light commercial compressors are hermetically sealed compressors there is not much else you can do if there is a problem with the compressor when fidning problems with air conditioners. Going from the compressor to the condenser coil in air conditioner troubleshooting it is important the condenser coils have the proper amount of airflow flowing through the condenser coils. Many times in troubleshooting air conditioning the condenser coils are plugged by dirt and debris and need to be cleaned. Turning the power off to the unit before washing the coils is advised. When troubleshooting the air conditioner condenser airflow of the condenser it is also important to make sure the condenser fan motor is working properly and turning at the proper RPM’s so the designed airflow is being pulled through the coils. If the condenser fan motor is not working at all the air conditioner will not function properly and it is possible you could cause severe problems with the compressor. If the fan motor is not working then it could be a bad motor or a bad relay or contactor that controls the fan motor. Proper knowledge of electro-mechanical controls and electric motors will help understand the problem much quicker when making repairs to air conditioners.

Air Conditioning Controls

When seeking problems with air conditioning systems it is very good that a highly skilled technican understands basic air conditioning controls. From the thermostat to any relays or contactors in the air conditioner system a thorough knowledge and understanding of these components and devices will make the air conditioning troubleshooting process easier for the technician. Many modern air conditioning systems use printed circuit boards for control of some components however there are still contactors and relays in the system that control fan motors and the compressor in the air conditioner system. Finding a problem air conditioning control is really easy even though it looks or appears to be a complicated thing when looking at a control circuit board. One basic rule of troubleshooting a circuit is that the circuit board needs a source of power and that when powered it will have a sequence of operation based on input from the thermostat and any safety circuits in the air conditioner system. You check the input voltage and based on the sequence of operation you check the output. If you do not have input to the board then you need to check the source and fix that before proceeding. If you have input to the board but no output then you need to check why there is no output. Perhaps there is a problem with the board or the safety circuit is open somewhere which will prevent the output from occurring. With relays and contactors in air conditioner troubleshooting you need to understand that something is controlling the relay or contactor with control voltage and that the relay or contactor has a function to either open or close based on the control voltage and where the control voltage comes from. For the most part relays and contactors in a typical air conditioner system are controlled by the thermostat. When the thermostat calls for air conditioning it closes some contacts in the thermostat. This completes the circuit for the control voltage. That process sends control voltage to either a relay or a contactor or both. When the relay or contactor or both close the contacts inside the relay or contactor close completing another circuit which is typically line voltage. This line voltage energizes compressors and fan motors and the system starts. If one was to learn ladder logic then one can understand the sequence of operation as designed by the design engineer and the air conditioning problem solving process becomes simpler. That is if the air conditioner comes with a ladder logic diagram. Many air conditioners do not come with a ladder logic diagram but with a component pictorial diagram. A good technician can take a pictorial diagram and draw their own ladder logic diagram so they can better understand sequence of operation for the air conditioner system.

The bottom line to finding and fixing air conditioner problems is to understand the basic components of the system and then break the system down into parts. When seeking problems with air conditioning a good technican can easily and quickly identify the part of the system which is causing the failure and make appropiate repairs to the system. Much of this comes from learning the air conditioning system system and part of it comes from field experience. Taking a course in HVAC and air conditioner controls and refrigeration will help you understand these processes and make you more efficienct at repairing air conditioners.

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Condensation Dripping In Crawlspace
written by Jay Petty, June 01, 2010

I am buying a newly constructed home. The Trane XR13 air handler is dripping water on top of the moisture barrier in the crawlspace. There is a white fungus on the wooden floor system near the unit. Is this unusual? How do I prevent this from continuing and spreading to other floor beams? Thank you.

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liquid line
written by ram, June 15, 2010

I have a unit that the liquid line is cool at the outdoor unit and the air temp. is not as cool coming out of the supply registers. Need some help?

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written by scott curry, July 12, 2010

I have a unit that has very suction pressure about 30 and very high head pressure 225 to 250 when the unit is running. When it shuts off the suction pressure rises. What do you think is my problem?

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Do not work with new or dirty filter
written by Darryl, July 13, 2010

My air condition unit went out, until I removed the air filter then it worked. I went to the store and replaced it with a new filteer and it went out again. It seems to only work when no filter is in it now.what do you think.?

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changeing my trne air condenser unit to a lennox
written by tom leavitt, July 19, 2010

i recently had a ac technician come servicwe my trane outdoor compressor,shortly after he left it blew up! I purchased a used lennox to replace it, heres my problem: i have a carrior programable thermastat inside and when i disconnected the trane there was only two wires running to it from the therm. Now the lennox has a totally differant way of lableing there unit as well as the carrier therm..
Can anyone tell me which terminals i hook the therm. wires to? There was a blue and brown wires in the trane.
any and all help would be apreciated, thank you

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written by David L., August 01, 2010

I own a Lennox model XC14-036-230, 14.2 SEER, 3 ton Elite condensing unit. This unit is less than a year old.

Problem: AC unit will jump start during severe lightning storms, and it emits a loud "LOW" pitched noise, which I am guessing that it's coming from the compressor.

Need some help?

Note: During normal operation it emits a HIGH pitched noise.

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