Air Conditioning 101

The descriptions and pictures below are designed to foster a basic understanding of the parts of your air conditioning system.  When you call for service, we hope they will help you to identify those parts of your system that may need service.  When you receive an invoice from us, we hope the information below will help clarify which parts and systems we worked on during our service visit.

breakerThe outside part of the air conditioning system is usually powered by a double pole circuit breaker in the breaker box.  An extremely common cause of no air conditioning is a circuit breaker in the off position.




The outside disconnect is used to switch power on and off to the outside condenser.  Again, an extremely common cause of no air conditioning is the outside disconnect in the off position.


_1080031York Affinty AC outside


The outside AC condenser’s job is to remove the heat from the refrigerant so that it can be sent back inside to absorb more heat.





The refrigerant goes back and forth between the outside condenser and the inside AC coil in copper tubes called the line set.  The larger copper pipe is typically insulated to reduce sweating of the copper pipe inside.




The line set connects to the outside condenser at the outside service valves.  This is also where we can connect our service gauges to see what the pressures are inside the AC refrigerant system and where we add and remove refrigerant.



The filter dryer is designed to remove moisture from the refrigerant – if there is water vapor in the lines it will freeze and stop the cooling.




UntitledcontrolwirerotatedThe AC system’s thermostat inside is connected to the outside condenser via a control wire that turns the unit on and off.  These wires are sometimes insulated with corn based insulation that is very tasty to mice – during the winter they have a feast and in the summer the AC condenser won’t turn on because of shorted control wires!  Please visit our page on rodent prevention measures to protect your system.



The outside fan motor is designed to pull air through the outside coil and up through the middle, removing heat from the refrigerant so it can absorb more heat from inside the building.



IMG_1485rotatedThe outside capacitor is used to help start the compressor and fan (sometimes only one capacitor is used and sometimes there are two).  The older capacitors lasted much longer than the new ones – sometimes they only last a cooling season.  As the compressor ages, sometimes it needs extra help in starting in which case a “hard start” boosting capacitor is used.





The outside contactor is controlled by the thermostat inside – whenever there is a call for cooling, a control signal is sent outside to the contactor which then sends 240 volts to the compressor to start it.  As with capacitors, the quality of contactors has declined precipitously and they too might last only one cooling season.



IMG_1410rotatedWith more modern equipment, the outside control is more sophisticated but more vulnerable to power quality and damage from mice.  Please visit our pages on the Aging Vineyard Grid and damaging voltage drops and Rodent Prevention.







The copper line set connects the outside condenser to the AC coil inside the house.






The AC coil is inside the air handler, the large unit in the basement connected to the ductwork which also has a blower.  An air handler (or fan coil) is different from a furnace in that it has no combustion inside.


The EC_CAPVU_Large AC coil can also be connected to a propane furnace as a cased coil.  The uncased picture depicts the fins that are housed inside the coil casing.






Inside the furnace or air handler is a blower motor that sends air through ductwork throughout the home.  This blower motor is connected to a “squirrel cage” wheel with blades around its periphery.





This blower motor is controlled by the indoor control board which takes the signal from the thermostat.




The cold AC coil condenses a lot of water vapor out of the air stream in the form of condensate.  This is then collected in a drain pan and sent to a condensate pump.  This pump sends the water outside via a small vinyl tube.  Sometimes the condensate pumps fail and a large puddle forms under the air handler.




The whole process is controlled by the inside thermostat.  If there is no cooling, one of the first things to check is that the thermostat is in the cooling mode.







Our goal is to be Martha’s Vineyard’s premier plumbing and HVAC shop – we appreciate the opportunity to service, install, and rescue your air conditioning system!