When a technician is troubleshooting a problem with any piece of equipment it is important that the technician understands the 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 equipment. However, it is important to understand the sequence of operation for an air conditioner so the technician can troubleshoot the air conditioner system.
The Evaporator Coil
Evaporator Coil – the evaporator coil is responsible for absorbing heat into the coils and the refrigerant. The evaporator coil is an essential component of vapor compression refrigeration. This is usually done as result of passing air or water over the evaporator coil where a heat exchange process takes place. Heat leaves the air or water (whatever medium is used) and is absorbed into the coil and the liquid refrigerant. As more and more heat is absorbed by the evaporator coil and the refrigerant again changes state from a liquid to a refrigerant vapor. By the time the refrigerant leaves the evaporator coil the refrigerant should be all vapor and ready to be received again by the refrigeration compressor.
The evaporator coil is typically inside the air handling unit or it can be installed in the duct work near the air handling unit. When the air handler blower turns on and the condenser is running refrigerant flows from the compressor through the condenser coils and then through the metering device. and into the evaporator coil. The refrigerant changes state in the evaporator coil and again in the condensing unit. In the evaporator coil the change of state is from a liquid to a vapor while in the condenser the change of state is from a vapor to a liquid. This is all necessary for the process of refrigeration to work properly. The typical evaporator coil is constructed of copper with aluminum fins surrounding the copper coils. The aluminum adds surface area to the copper coils and enhances the heat exchange rate making the coils more efficient.
Components of Vapor Compression Refrigeration – The Evaporator Coil
Refrigeration Pressure Switches
Richard – What are refrigeration pressure switches used for in refrigeration circuits and how do refrigeration pressure switches protect the system from further damage?
Thanks for the question and for being a reader of High Performance HVAC! First there two types of basic refrigeration switches in the typical high grade residential system. I say high grade because not every refrigeration system in air conditioners and heat pumps have refrigeration switches to protect the refrigeration system.
High Pressure Refrigeration Switch – The high pressure switch will kill the compressor circuit if the pressure exceeds the rating on the pressure switch. These pressures will vary depending on the type of refrigerant the air conditioner or heat pump uses in the system. On some air conditioners or heat pumps this switch is manually reset only simply because if it trips there is definitely a problem that needs to be resolved before the system should run again. On Rheem and Ruud heat pumps and air conditioners the reset button is usually red on located near the control panel. A simple push of the switch will reset the switch and the operation of the air conditioner should return to normal until the pressure exceeds the rating of the switch. Things that can cause the pressure switch to trip include:
- Bad condenser fan motor
- Coils plugged up with dirt and debris
- Fins on the coils bent
- Blockage in the refrigeration system
These issues, if they exist, should be taken care of before before the switch is reset. The high pressure switch prevents the system from operating at extremely high pressures.
Low Pressure Switch – The low pressure switch is typically an automatically reset switch that will reset itself when the pressure on the low pressure side of the refrigeration systems returns to normal or above the setting on the switch. When a refrigeration system operates at lower than normal pressures the system can freeze up with the freezing beginning at the evaporator coil and working its way back to the compressor via the suction line. Freezing of the refrigeration system is bad and lead to liquid refrigerant slugging in the compressor which can lead to compressor failure. Things that can cause the low pressure switch to trip include:
- Low refrigerant charge from a refrigerant leak
- Blower motor failure in the air handler
- Plugged evaporator coils or a blockage of air flow
- Failure of a refrigeration component in the refrigeration system
Again, if these issues exist in the refrigeration system they need to be addressed to prevent the low pressure refrigeration switch from tripping.
10 SEER units cannot be purchased in the US any longer. The new standard as mandated by the Department of Energy as of January 2006 is 13 SEER. This 30 percent increase in efficiency from 10 SEER requires a change out of the inside coil. In 2011 the Senate is proposing a new SEER and AFUE standard that will be based on where you reside in the USA. The country will be split up into three regions. Northern, Southern, and the Southwestern regions with each region having different efficiency standards. The proposed efficiency standards for each region are as follows: Continue reading “2011 Proposed Increase in SEER – EER – AFUE – HSPF” »
This freshly rebuilt reciprocating compressor is destined for a large commercial chiller. Chillers chill water for air conditioning. Compressors compress refrigerant vapor and pump the compressed refrigerant to the condenser to be condensed into a liquid. The compressor provides compression which is an integral part of the refrigeration process. The old compressor was condemned for electrical burn out. The windings in the old compressor burned up and caused the circuit breaker to trip. Continue reading “Refrigeration – HVAC Compressor Rebuilt” »
Air conditioners and heat pumps use the process of refrigeration to provide heating and cooling. What is the definition of the process of refrigeration? Refrigeration is the process of moving heat and depending on whether it is a heat pump or air conditioner and what mode it is in will depend where you are moving the heat. An air conditioner and a heat pump (in the cooling mode) will move heat outside. The evaporator coil absorbs the heat and the condenser rejects the heat. Continue reading “Refrigeration for Air Conditioning and Heat Pumps” »
In air conditioning and heating applications it is necessary to accurately measure temperature to offer control of the temperatures relative to the application for which the HVACR equipment is serving. There are four separate temperature scales used to measure temperature and it becomes necessary at times to have the ability to convert between the different scales. The two most common scales used by most people are Fahrenheit and Celsius. Fahrenheit is mostly used in the United States where the culture has resisted changing from standard measurements to the metric system. Celsius is used throughout the world including the United States and Canada. Scientist often use Kelvin and Rankine measuring scales to measure temperature. These temperature scales, Rankine and Kelvin, are uncommonly used in popular culture no matter where you live in the world except by the scientific community and are often used to measure extreme temperatures. Continue reading “Temperature Measurement & Conversion for HVACR” »
HVAC refrigeration leaks (also referred to as freon leaks) can cause serious issues with HVAC heat pump equipment. HVAC refrigeration circuits are designed and built to hold the refrigerant. It is a sealed hermetic system. The HVAC refrigeration circuit should never need refrigerant. An HVAC refrigeration system does not burn refrigerant. The refrigerant is used over and over again to move heat from one place to another. Aside from a leak, once the refrigeration system is properly charged, the system should never need refrigerant for the life of the equipment. Continue reading “HVAC Refrigerant Leaks – Freon Leaks – Old Leaking Condenser Coils” »
Air Handler Unit Components: Hot Water Coil Heat
Hot water coils inside of air handler units combine a boiler system or a special capacity hot water heater and forced air to provide forced-air heating. The concept is simple and used a lot in commercial and some in residential. Commercial systems almost exclusively use a boiler to provide hot water to the hot water coil inside the air handler unit while the residential systems use mainly special capacity hot water heaters to provide hot water to the hot water coil inside the air handler unit. On a call for heat a pump is energized to begin the circulation of hot water from the heating source to the coil. The air handler unit blower motor energizes and air begins to move across the coil. Heat is exchanged from the hot water coil to the air and the air is delivered to its appropriate destination through the ductwork.
Air conditioners work by removing the heat from the space they service. An air conditioner is simply a big refrigerator that uses the process of refrigeration to provide cooling for a building. Air conditioners work by using direct expansion coils or chilled water coils to absorb and move the heat from the air as air is blown across the coils. Types of air conditioner systems that use direct expansion coils for cooling are window units, split system air conditioners, package unit air conditioners, packaged terminal air conditioners like the air conditioners used in hotels, and mini-split ductless air conditioners. Air conditioners which utilize chilled water for air conditioning are typically commercial air conditioners for large commercial buildings. It doesn’t matter what type of air conditioner is used the coils in the air conditioner system are brought to a temperature colder than the air. These air conditioners coils are designed with materials like copper or aluminum to absorbed heat easily and pass this heat to the refrigerant whether the refrigerant is Freon or another type refrigerant chemical or whether that refrigerant is water. Any type of refrigerant is designed to absorb heat. That is how air conditioning works. Continue reading “How Air Conditioning Works” »