Basic Air Conditioner and Heat Pump Components

As with air conditioning systems and heat pump types, there are a wide array of different components that one can find in an air conditioner or heat pump unit. Regardless of how many bells and whistles or air conditioning and heat pump parts one can get on an air conditioning or heat pump system this article will focus on the basics and a few necessary bells and whistles that you won't get with a builders grade HVAC unit. Typically, builders grade systems are basic systems without any bells and whistles but for technical reasons it is recommended that one have some extras installed in a builders grade HVAC system to add longevity and efficiency to the the system.  From builders grade HVAC systems in residential to HVAC systems complete with state of the art building automation systems in commercial buildings many of the air conditioning and heating components components described here are the same.

• Thermostat - almost all the thermostats made today are digital thermostats but there are still a lot of old mercury-type thermostats out there. Digital thermostats are recommended because many of them come with a built-in timer delay to prevent short cycling of the air conditioner or heat pump compressor. These also can be purchased in programmable or non-programmable types. Programmable thermostats are recommended for people or a regular schedule. Non-programmable thermostats are recommended for people who are home most of the day.
• Condenser or Condensing Unit - the condensing unit sits outside (on split HVAC systems and mini-splits). This is where the refrigerent (R-22 or R-410A) is compressed with the compressor and has heat removed from it while moving through the coils. For heat pump application, the condenser coils absorb heat from the atmosphere. Condenser coils can be either aluminum or copper and the higher SEER HVAC units have a larger coil area for better efficiency. It is important to keep these coils clean.
• Reversing Valve (Heat Pumps Only) - the reversing valve is found in heat pumps only and is activated from the thermostat when the setting is changed to air conditioning mode except for Rheem or Ruud brands. In other words, if this valve were to fail it would fail to heat except for the above mentioned HVAC brands.
• Evaporator Coil - the evaporator coil (for split HVAC systems and mini-splits) is the coil found inside the air handler or near the furnace. As air passes over the evaporator coil heat from the air is absorbed into the evaporator coils and the refrigerant inside the evaporator coils. The heat is then transferred outside where it is rejected into the atmosphere by the condensing unit. An evaporator coil for a heat pump does the opposite. The evaporator coil for a heat pump gets very hot in the heat mode. As air passes over the coil the heat is transferred from the coil to the air. This is opposite of the HVAC air conditioning cycle. In air air conditioning mode the heat is absorbed inside and rejected outside. In heat mode on heat pump applications, the heat is absorbed outside and rejected inside. It is important to keep these coils clean by maintaining a good filter maintenance schedule.
• Metering Device - typical of the newer higher SEER HVAC equipment are thermostatic expansion valves or TXV's. TXV's work using superheat. It is not in the scope of this desciption to get overly technical but in simple terms a TXV meters the refrigerant based on specific demand. If it has a heavy load the TXV will meter more refrigerant to the coil. A light load the TXV will meter less refrigerant to the coil. Heat pumps have TXV's in the HVAC condenser and on the evaporator coil. Other types of metering devices are fixed orifice (piston) or cap tube type.
• Condenser Fan Motors - it is necessary to move air over the condenser coils so a fan is necessary. Manufacturers are beginning to specify their higher SEER units with variable speed motors (technically referred to as ECM or Electronically Commutated Motor). The ECM motors will turn at a specific speed based on demand so only the energy needed is expended.
• Blowers - Blowers move the air across the HVAC evaporator and throughout the dwelling. More common than condenser fan motors, manufacturers are beginning to specify their higher SEER units with variable speed motors (technically referred to as ECM or Electronically Commutated Motor).
• Compressors - most common in residential and commercial are scroll and reciprocating compressors with scroll compressors leading the way in the higher SEER units. New two-stage scroll compressors are beginning to be specified in higher SEER equipment. Variable speed compressors will be the next big jump in compressor technology and will extra efficiency over anything available today.
• Additional Bells and Whistles - it is recommended that HVAC systems have additional features such as delay timers to prevent compressor short cycling, high and low pressure switches for additional compressor protection, and for heat pumps, an outside temperature sensor that will turn the outside condensing unit off when it becomes ineffective at heating and engage the back-up heat. Call your local heating and cooling HVAC contractor to review these bells and whistles. They can install the HVAC components in your system for added HVAC equipment protection and efficiency.

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