Air Conditioner Blower Control

This invention relates to a control circuit for a home heating and air conditioning system and, more particularly, to provide multiple speed capability to the home heating and cooling unit with a significant savings in energy during the cooling season.

In the past, home heating and cooling systems have had one centralized control unit with a thermostat selector switch that may be positioned in the heat, cool or OFF position. Also, a fan selector switch is normally located in the centralized control unit with the fan either being turned to the automatic position or to the ON position. The thermostat, which normally indicates if either heating or cooling is necessary, is normally located within the centralized control unit. During the heating season, if the fan selector switch is on automatic, the evaporator fan relay causes the blower to operate at a lower speed during the heating cycle. During the cooling season, if the thermostat selector switch is in the cool position and the fan selector switch is in the automatic position, upon the thermostat calling for cooling, an evaporative fan relay is activated to switch the multiple speed blower motor to a high speed. This allows for maximum heat transfer from the evaporator coils to the cooled space due to the large volume of air flow over the evaporator coils during the operation of the compressor. If the fan selector switch is in the ON position when the thermostat selector switch is in either the heat or the cool position, then the multiple speed blower motor will continue to operate at high speed regardless of whether or not the thermostat is calling for heat or cooling.

In U.S. Pat. No. 3,454,078 issued to Elwart, there is shown a blower motor that may be operated over an infinite range of speeds. However, to operate the blower motor, a diac and triac combination is used to vary the speed of a split phase motor. There is a considerable amount of energy loss in the triac requiring special heat sinks. Heat sinks are also required for the blower motor because a true sign wave is not being fed to the windings. This results in a large amount of total energy loss, even though the blower motor may be operated over a wide range of speeds. Motors other than split phase motors having either a shaded pole or capacitor run will have a tendency to burn up during repeated operation. Further, Elwart is dependent upon the accuracy of thermistors, as well as a photocell operated by a low voltage lamp. If the blower in Elwart is operated at any speed other than the high speed, there will be a large amount of energy loss because the waveform supplied to the blower motor is not true sign waves as would be the case with the present invention. There is no suggestion in Elwart to change the speed of the blower motor during the cooling season with a sinusoidal waveform, which change is dependent upon the position of the thermostat and the operation of the compressor.

It is an object of the present invention to provide a home heating and cooling system with multiple speed capabilities during the cooling cycle.

It is another object of the present invention to provide a control unit for a home heating and cooling system wherein the blower motor is operated continuously during the cooling season with the blower motor operating at a low speed when the compressor is OFF and at a high speed when the compressor is ON.

It is another object of the present invention to provide an energy saving modification for a home heating and cooling system wherein the blower motor is continuously operated at a low speed when the compressor is OFF thereby providing continued air circulation inside of the cooled area to eliminate hot air pockets and provide continued air circulation. The continued air circulation will result in the body feeling comfortable at a higher temperature due to air circulation over the skin. Therefore, the higher setting of the thermostat results in a decrease in the operation time of the compressor which is the major power consumer in the air conditioning system.

It is even another object of the present invention to modify the control unit of an existing heating and cooling system having a multiple speed blower motor. The existing heating and cooling system would include a thermostat selector switch having a heat, cool and OFF position, a fan selector switch and a thermostat. An economizer control relay is connected through the cool contact of the thermostat and the cool contact of the thermostat selector switch across a 24 volt transformer to energize the economizer control relay. Energization of the economizer control relay will open a normally closed contact connected to the low speed terminal of the multiple speed blower motor, and close a normally opened contact connected to the high speed connection of the multiple speed blower motor. By having the fan selector switch in the ON position, the evaporator fan relay is energized thereby allowing power to be continuously supplied to the normally open and normally closed contacts of the economizer control relay. Therefore, when the thermostat moves to the cool position, the contactor relay is energized to turn ON the compressor, and the economizer control relay will also be activated to switch the multiple speed blower motor from a low speed to a high speed. The normal operation of the heating cycle is not changed.

The FIGURE is a schematic illustration of a control unit for a heating and cooling system embodying the present invention.

Referring to the drawing, a typical control unit for a home heating and cooling system embodying the present invention is shown. The control unit embodying the present invention is represented generally by reference numeral 10. A 115 volt rms AC voltage is supplied through the input terminals 12 and 14 to the primary winding 16 of a stepped-down transformer 18 with the voltage across the secondary winding 20 typically being 24 volts. Also connected to input terminal 12 is a common lead from multiple speed blower motor 22. High and low speed connections of the multiple speed blower motor 22 connect through relay contacts and a furnace fan switch 60 to input terminal 14 as will be subsequently explained in more detail.

A secondary winding 20 of a transformer 18 connects to the cool contact of a thermostat selector switch 24 having a wiper arm 26. The wiper arm 26 may be manually adjusted from the cool position to a center OFF position or to a heating position. In the heat position, the wiper arm 26 connects to a heating primary control 28. While the heating primary control 28 is not explained in detail herein, it would include the typical elements, such as a pilot light, gas valve, and other related controls not specifically shown herein. The heating primary control 28 connects to the opposite side of the secondary winding 20.

Connected to the same side of the secondary winding 20 as the heating primary control 28 is contactor coil 30, economizer control relay 32 and evaporator fan relay 34. The opposite side of the contactor coil 30 connects through a normally closed, low pressure switch 36 and a normally closed, high pressure switch 38 to the cool contact of the thermostat 40. Thermostat 40 has a wiper arm 42 which may be of the typical bimetal construction. Also connected to the cool contact for the thermostat 40 is one side of economizer control relay 32. The heat contact for thermostat 40 connects directly to one side of the secondary winding 20 of the transformer 18. The ON contact of a fan selector switch 44 also connects to the heat contact of thermostat 40 and the same side of the secondary winding 20. The wiper arm 46 of the fan selector switch 44 may be in the ON or automatic position. The wiper arm 46 of fan selector switch 44 is connected to one side of evaporator fan relay coil 34.

Connected to terminals 48 and 50 is a suitable 230 volt rms AC voltage which is fed to normally open relay contacts 52 and 54 of contactor coil 30. The opposite side of the normally open relay contacts 52 and 54 are connected to each respective side of a parallel connection for a compressor 56 and a condenser fan motor 58.

During the normal operation of the control unit 10 in the heating season, the wiper arm 26 of the thermostat selector switch 24 is in the heat position. If the wiper arm 46 of the fan selector switch 44 is in the automatic position, upon the wiper arm 42 of thermostat 40 moving to the heat position thereby indicating additional heat is necessary, one side of the secondary winding 20 will be connected through the wiper arm 42 of the thermostat 40 and the wiper arm 26 of thermostat selector switch 24 to supply energy to the heating primary control 28. The supplying of voltage to the heating primary control 28 causes the furnace to start the heating process. Once the temperature inside of the furnace has reached a predetermined point, the furnace fan switch 60 will close. Because the evaporator fan relay coil 34 is not energized, 115 volts AC is fed through the normally closed relay contact 62 and the furnace fan relay 60 to the low speed side of blower motor 22 thereby causing the blower motor 22 to operate at a low speed. When the thermostat 40 has sensed that the room temperature is at the desired level, the wiper arm 42 will move to the cool position thereby removing the energy being supplied to the heating primary control 28 to shut OFF the furnace. However, the furnace fan switch 60 will not open until temperature inside of the furnace has decreased below the amount preset in the furnace fan switch 60.

If the wiper arm 46 of the fan selector switch 44 is in the ON position, then the evaporator fan relay coil 34 is energized and opens normally closed relay contact 62 and closes normally open relay contact 64. Since the economizer control relay coil 32 can never be energized when the wiper arm 26 of the thermostat selector switch 24 is in the heat position, 115 volts AC will be supplied between the low speed terminal and common of blower motor 22 via normally open relay contact 64 of evaporator fan relay coil 34 and normally closed relay contact 66 of economizer control relay coil 32. In this case, operation of the furnace fan switch 60 in the thermostat 40 will have no effect on the low speed operation of blower motor 22.

Assume now that the wiper arm 26 of the thermostat selector swtich 24 is in the cool position. If the wiper arm 46 of the fan selector switch 44 is in the automatic position, the evaporator fan coil 34 will be energized upon the wiper arm 42 of the thermostat 40 moving to the cool position. By energization of the evaporator fan relay coil 34, the normally open relay contact 64 would close thereby supplying 115 volts AC through either normally closed relay contact 66 or normally open relay contact 68 of economizer relay coil 32. It should be realized that the furnace fan switch 60 remains open during the entire cooling season.

Since the economizer control relay coil 32 also connects through wiper arm 42 of thermostat 40 when the wiper arm 42 is in the cool position, and the wiper arm 26 of the thermostat selector switch 24 to the secondary winding 20 of the transformer 18, the economizer control relay coil 32 is energized which causes normally closed relay contact 66 to open and normally open relay contact 68 to close. Therefore, each time the evaporator fan relay coil 34 is energized (with the fan selector switch remaining in the automatic position), so is the economizer control relay coil 32 therefore supplying 115 volts AC via normally open relay contacts 64 and 68 to the high speed terminal of multiple speed blower motor 22.

If the refrigerant in the compressor 56 has the necessary charge, normally closed, low pressure switch 36 will remain closed. Also, the normally closed, high pressure switch 38 will remain closed if the compressor 56 is not overcharged, does not overheat or otherwise malfunction causing the switch to open. Therefore, during normal operation, switches 36 and 38 will be closed and contactor coil 30 will be energized upon movement of the wiper arm 42 of thermostat 40 to the cool position if the wiper arm 26 of thermostat selector switch 24 is also in the cool position. Upon the thermostat 40 calling for cooling by movement of wiper arm 42 to the cool position, the contactor coil 30 will be energized and the normally open relay contacts 52 and 54 closed. The closing of the normally open relay contacts 52 and 54 connects the 230 volts received at terminals 48 and 50 across the compressor 56 and the condensor fan motor 58. The position of the fan selector switch 44 has no effect on the operation of the contactor coil 30.

Assume now that the wiper arm 46 of the fan selector switch 44 is moved to the ON position. Evaporator fan relay coil 34 will remain continuously energized thereby opening normally closed relay contact 62 and closing normally open relay contact 64. Therefore, when the wiper arm 42 of thermostat 40 is in the heat position and the wiper arm 26 of the thermostat selector switch 24 is in the cool position, the economizer control relay coil 32 is not energized. When the economizer control relay coil is not energized, 115 volts will be connected to the low speed terminal of multiple speed blower motor 22 via normally closed relay contact 66 and normally open relay contact 64. Upon the wiper arm 42 of the thermostat 40 moving to the cool position indicating cooling is necessary, both the contact coil 30 and the economizer control relay coil 32 are energized. Energization of the economizer control relay coil 32 will open normally closed relay contact 66 and close normally open relay contact 68 thereby applying voltage to the high speed terminal of the multiple speed blower motor 22. Simultaneously, the compressor 56 is energized. Therefore, by inclusion of the economizer control relay 32 with its respective normally closed relay contact 66 and normally open relay contact 68, the multiple speed blower motor 22 is operated at a low speed when cooling is not required and at a high speed when cooling is required. During the heating season, the economizer relay coil 32 and its relay contacts 66 and 68 will have no effect on the normal operation of the heating and cooling system.

By use of the economizer control relay coil 32, the multiple speed blower motor 22 can be continuously operated during the cooling season at a low speed when cooling is not required thereby insuring a continued air circulation in the cooled area. The continued air circulation prevents hot air pockets, and causes individuals located inside the cooled area to sense the moving air over their bodies. The moving air over an individual's body tends to increase the temperature at which an individual is comfortable thereby resulting in high settings for the thermostat 40. Since the compressor 56 is the main source of energy drain, by the decreasing the ON time for the compressor 56 by higher setting of the thermostat 40 results in a substantial energy savings even though the blower motor 22 is continuously operated at a low speed when the compressor 56 is OFF. The multiple speed blower motor 22 must operate at a high speed when the compressor is ON to insure the maximum heat transfer through the evaporator coil (not shown) and the vaporization of the refrigerant contained therein.