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Artist's rendition of home air conditioning system.

Artist’s rendition of home air conditioning system.

Many homeowners are not aware of the process by which their heating and air conditioning system works. Most only know how to operate the thermostat and change the air filter. Here is a simple synopsis of how air conditioning systems and heat pumps work.

Homes that utilize air conditioners or heat pumps typically use a split system. This means it has condenser outside and an air handler or furnace inside. Two copper refrigerant lines connect them. The larger pipe has a black foam insulation covering, and the smaller one is uncovered. Running along the ceiling or walls to each unit, both lines are typically field brazed onto the condenser, then inside to the evaporator coil. Since homes have varying sizes and construction, the sizing of those units are very important. This and ductwork installation make the difference between comfort and discomfort.

Assuming that all things are correct, the following should occur:

  1. The thermostat when calling for cooling should do two things at call: activate the fan or blower for air movement through system to registers, and start the outdoor unit. Note that some units have a built in delay when the condenser (outdoor unit) will start first. Then the fan or blower inside starts a short time later. When both are operating, think of them at this point as heat exchangers transferring heat from one to another. In cooling mode, the evaporator coil located inside an air handler or upstream from a furnace is absorbing heat and humidity. If you could see the coil, it resembles the radiator on a vehicle. Your indoor fan blows air through that coil from return ducts, bringing the heat and humidity from the home’s interior to be transferred. Since refrigerants absorb heat readily, their chemical properties change from liquid to vapor before leaving the coil, using a metering device for refrigerant flow. The compressor is a pumping mechanism driving the refrigerant. It is located inside the outdoor unit. The process also allows the humidity in homes to form in visible droplets of water, draining into a collecting pan, then piped to a common home drain.
  2. Once the condenser (outdoor unit) has the vapor pumped to it, its outdoor coil with the compressor then condenses the gas back to a liquid. It transfers heat it absorbed from inside the home to the air via its fan, visible from outside. This cycle continues until the thermostat has reached desired setting.

Heat pump and air conditioner differences

A heat pump’s cooling cycle is the same as a standard air conditioning system. However, the heating cycle that is not available with air conditioners has a couple features you need to know about:

  1. Defrost control and its sensor
  2. Reversing valve
  3. Outdoor metering device

When heat is needed, the typical heat pump system uses the same method as above. However, there is a mechanical difference. Instead of the indoor or evaporator coil absorbing heat from inside of home, the reversing valve reverses it. This is a mechanical device used to change the flow of the refrigerant located inside the outdoor unit.

How a heat pump works

Now the heat pump is absorbing the heat from outdoors, changing it to the evaporator. It’s hard to believe that when it is cold outside, much of the heat is available from the ambient air. However, the heat pump transfers this heat inside via the compressor through the refrigerant lines. There, an indoor fan sends heat through the home over a heated coil. You can heat a home at much lower operating costs than fossil fuels, when outdoor temperature stays above freezing.

Heat pumps, while in heat mode, must absorb heat from outside air. However, to do this, their coil temperature must be colder than the surrounding air. With that comes a frost pattern that over long periods forms on coils, most noticeably seen in colder temperatures. A defrosting control cleans the unit so air can freely cross coils. Otherwise, heat will not transfer properly. That’s when homeowners call us stating their units are on fire or their outdoor fan is burning up. Since the defrost cycle stops the fan and reverses the flow of refrigerant to heat up and clean off the coil, steam and odd noises usually accompany this for up to ten minutes.

Not to fear, though. This is normal in colder temperatures. Sometimes multiple heating cycles can happen before defrosting takes place. If all is running correctly, the system’s thermostatic control will reach the desired temperature, turning off the system. Thus, it completes the typical heat pump cycle.

Contact us today for your air conditioning and heat pump needs!

Hopefully, this gives you some insight and answers some questions you may have. Naturally, I have not included all the details, but given a general overview. Calling Sam the Furnace Man is always the right solution to your home’s comfort needs.

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