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Residential Thermostat Calling or Switching for Heating
The first thing that must happen is that the heat pump control thermostat must provide a voltage signal to the indoor air handler or electric unit. The thermostat can be most understood as simply a switch that turns a low voltage 24 volt power on and off to the respective terminals.
In the case of the heat pump thermostat calling for heating or cooling the thermostat switches on the power from the “R” terminal which is the 24 volt power source to the “Y” terminal on the thermostat which is in essence the call for the outdoor unit compressor to run. These terminals are located on the back or on the wall mounted face plate of the thermostat.The heat pump thermostat determines the mode of operation, cooling or heating, by switching the power from the "R" terminal to the reversing valve located in the outdoor unit, this terminal on the heat pump thermostat is most often the "O" or "B" or "O/B" terminal.
Most heat pump thermostats also have either an emergency heat or second stage heating terminal as well, this controls when the back up heat turns on and the thermostat switches the power from the "R" terminal to the "E" terminal for the back up emergency heat, this is usually only active when the thermostat emergency heat switch or mode is selected to be on manually. The second stage or back up heat source, which is basically the same as the emergency heat except that it is automatic and does not require the operator (that's you) to manually turn it on. this is normally accomplished by the thermostat switching power from the "R" terminal to the "AUX" or "W2" terminal.
All the wires connected to the thermostat will usually always go directly to the air handler or electric furnace and if wired correctly most of the specific terminals that the wires are connected to will match at both the thermostat and at the furnace. For instance the wire connected to the “Y” terminal should be the same wire at both the thermostat and the air handler or electric furnace heating system.
One important thing to note is that all electrical circuits must have both a positive and negative side to complete the circuit, much like a battery has both a plus ” + “ and a minus ” – “ side. Without both the positive and negative sides this electrical circuit will not be complete and will not function.
Most digital and programmable thermostats, thermostats with an LCD display of some type, will have both the positive and negative. Some other types are either battery powered or are not digital but are simply some sort of a mechanical switch and do not have the negative circuit at the thermostat. Regardless the negative side of the circuit at the thermostat is normally used only to power the thermostat itself.
For the purpose of understanding where the positive and negative are located on the thermostat and on the furnace in most if not all cases the positive side is always on the “R” “RH” or “RC” terminal and the negative side is almost always on the “C” terminal. The “RH” is usually designated as the heating power source and the “RC” is usually designated as the cooling power source and in most cases these are connected together. Most dedicated heat pump thermostats do not have the "RH" or "RC" terminals.
CAUTION - Always be very careful with electricity as it can be lethal, if you are not comfortable performing any of these steps please do not perform them, of course you are performing these steps at your own risk.
Important Note: The heating system control board is sometimes very sensitive to static electricity, avoid touching this board to prevent failure.
| ASI's HVAC and Home Improvement Articles Your money is literally flowing right out of your roof and crawl space! I can easily say that everyone has this problem, if you have an attic space and we all do, then you are wasting countless dollars every minute of every day. Easy Do It Yourself Energy Savings! Great Energy Savings from Hybrid or Dual Fuel Systems With the threat of energy prices increasing every year the idea of high efficiency and energy savings becomes more and more real to residents of the hydroelectric charged northwest. One approach that is very popular today is called a “dual fuel” heating system. First let’s define what a dual fuel system... The Geo-Thermal System Explained in a Nut Shell Geothermal is by far the highest efficiency heating and cooling system available today. While the systems require up to three times more investment upfront than a conventional heating and cooling system... Ameri-Serv, Inc. Heating and Cooling News Ameri-Serv Inc Helping the Treasure Valley Community Ameri-Serv, Inc. Heating and Cooling has successfully helped dozens of Treasure Valley Families with thousands of dollars worth of free maintenance services and repairs through this holiday... |
 
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ASI's Heating Related Articles
  If
your Gas Furnace is an older gas furnace (usually 10 plus years old) it
may have a standing pilot light like a water heater, if this is the
case carefully follow the instructions on the furnace to light the
pilot. Some models have an intermittent pilot light or spark ignition
and you can usually hear the the system try to light the pilot flame
with a spark .. |
  Maintaining
your gas heating furnace system is important both to help make the
system last longer and to help keep the operating costs as low as
possible. All furnaces should be cleaned and inspected annually and
there are some things you can do yourself to save money but everyone
should call a qualified technician to inspect the system every fall as
well as to make any necessary repairs. |
  The
first thing that must happen is that the control thermostat must
provide a voltage signal to the furnace heating unit. The thermostat can
be most understood as simply a switch that turns a low voltage 24 volt
power on and off to the respective terminals. In the case of the
thermostat calling for heat the thermostat switches on the .. |
  Homeowners
can help prevent failure of their oil or gas furnace heat exchanger by
simply maintaining their system regularly. This includes having an
annual inspection of the system which should always including cleaning
of the blower and cabinet. More importantly the homeowner needs to make
sure that they maintain and clean or change their system air filters |
SAFETY FIRST!
These easy to understand HVAC maintenance tips are for common tasks that
almost any homeowner can perform. Please do not perform these tips if
you are not comfortable performing
them. Electricity is dangerous and can cause serious injury or death,
always assume electrical power is on unless you have checked it with an
appropriate electrical meter. Understanding Electrical Circuits and Standard Household Voltages Heating and Air Conditioning Equipment have many moving parts such as fans and other devices, Always stay clear of fans and other moving parts as they can start at any time. Many electrical heating equipment operate at high voltages. All gas equipment and many other types operate using either natural or propane gas or fuel oil, always use extreme caution when working with flammable sources. It is always required to secure the power and gas or oil off to any equipment or appliance before performing service or repairs. Ameri-Serv, Inc. assumes no liability for
the use of the information provided on this website. Please always use common sense and make sure the electrical power is off before opening and accessing the inside of any equipment or appliance. Reaching into anything with electrical or moving parts can result is serious injury. Remember Safety is Always First
Breaking News: The Cost to Repair your old Air Conditioner just Skyrocketed
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13601 W McMillan Rd Suite 102-120 Boise, Idaho 83713 Office (208) 342-4328 Fax (208) 906-1282
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Copyright 2011. ASI Heating and Cooling a Division of Ameri-Serv, Inc. All rights reserved