Air Conditioner Sequence of Operation - When a technician is troubleshooting an air conditioner problem it is important that the technician understands the air conditioner sequence of operation for that equipment. When there is a problem with the equipment, including air conditioners, the technician will know the problem if the equipment or air conditioner does not follow the sequence of operation. Sometimes it is that easy, and other times it is not that easy when troubleshooting any HVAC equipment. However, it is important to understand the sequence of operation for air conditioning so the technician can troubleshoot the problem.

Air Conditioner Sequence of Operation | HVAC Cooling

Compared to other HVAC equipment, an air conditioner sequence of operation is fairly simple. An air conditioner follows the following basic sequence of operation:

1. The thermostat, set to cooling mode, calls for cooling. The switch inside the thermostat closes. That energizes the “Y” and the “G” circuit in the thermostat or the compressor contactor and the fan circuit.
2. The compressor contactor closes, and the condenser fan motor and the compressor turn on. That happens simultaneously as the compressor contactor controls both the compressor and the condenser fan motor. That is important because if the compressor contactor pulls in or engages and the fan doesn’t start, but the compressor does, then the technician knows there is a problem with the condenser fan motor and vice versa. If neither starts, but the compressor contactor is pulled in, then the technician knows there is either a problem with the contactor passing voltage across the contacts or a power problem possibly a breaker trip. If the compressor contactor does not pull in, then the tech knows there is a control problem.
   

   Condenser Fan Motor

3. At the same time, the compressor contactor is doing its job, the air handler blower fan relay closes (from the “G” contact in the thermostat) and energizes the blower fan. While the compressor gets the refrigerant moving through the refrigeration system, the fan begins moving air through the duct system and across the evaporator coil.
4. When the thermostat satisfies the “Y” and the “G” contacts in the thermostat opens de-energizing the compressor contactor and the fan relay. The compressor and condenser fan motor de-energize and stop operation. The fan, in heating and cooling mode (no matter what type of heat you have), will remain on because of a time delay in the air handler. That is to dissipate any cool or hot air left in the duct system. It adds efficiency to the system and makes use of any residual energy left in the system. In heating mode, it also allows for a cooling down of the heat left in the system.

Air Conditioner Sequence of Operation | The Basics

Adding some basics to the sequence of operation along with some field experience one can become competent in air conditioning troubleshooting. Some basics for becoming a good air conditioner technician include both practical and theory skills and knowledge:

• Ohms Law and HVAC circuits
• Basic HVAC Circuits including control circuits
• Understanding both run and start capacitors
• Understanding HVAC electric motors basics
• Understanding compressors and how to troubleshoot a hermetic compressor
• Refrigeration theory
• Refrigeration components such as metering devices and compressors
• Ductwork and airflow factors
• Basic safety for working around high voltage electricity and mechanical moving parts

Basic Air Conditioner Component Diagram

Finally, in conclusion, that is the basic sequence of operation used in millions of air conditioners all over the world. Essentially, the AC sequence of operation is how an air conditioner works. Even if you know the sequence of operation for an air conditioner there are many other problems that can occur that cannot be solved with this knowledge alone. Some things take education and experience to figure out. For an HVAC technician, this is basic and helps in solving air conditioning problems.

Air Conditioner Sequence of Operation

Technical Resource: Refrigeration and Air Conditioning Technology