Method and apparatus for wiring room thermostat to two stage HVAC system

• US 6,450,409 B1
• Filed: 11/15/2000
• Issued: 09/17/2002
• Est. Priority Date: 04/14/2000
• Status: Expired due to Fees

• Current Assignee: Sensata Technologies Massachusetts Incorporated (Sensata Technologies Holding Plc)
• Original Assignee: Texas Instruments, Inc.
• Inventors: Miller, Mark E., Bailey, Walter H., Rowlette, Mitchell R.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US09/714,029
• Time in Patent Office: 671 Days
• Field of Search: 621/75, 62/77, 622/98, 621/79, 621/80, 621/82, 236/1.E, 236/78.D, 236/1.C, 165/260, 165/261, 165/262, 165/256
• US Class Current: 236/1.00E
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 11/52 Indication arrangements, e.g. displays
• CPC Class Codes: F24F 11/63 Electronic processing
• CPC Class Codes: F24F 11/86 by controlling compressors within refrigeration or heat pump circuits
• CPC Class Codes: F24F 11/88 Electrical aspects, e.g. circuits
• CPC Class Codes: F24F 2110/10 Temperature
• CPC Class Codes: G05D 23/1912 whose output amplitude can take more than two discrete values

Abstract

A control used in a two stage HVAC system has a power supply from a 24 VAC transformer which is full wave rectified (D1, D2, D3, D4) to create DC voltages for a microcontroller (U1) and relays (K1-K3). All of the control information needed for the two stage control system is sent to the control from a room thermostat (12) having first and second stage cooling signal terminals (Y1, Y2) over a single line by connecting a diode between the Y1, Y2 terminals creating separate microprocessor recognizable signals.

Claims

1. In an HVAC system having a two stage control and relays, the control having a microcontroller having first and second two stage input signal terminals, a power supply from a transformer full wave rectified to create DC voltages for the microcontroller and relays, a two stage room thermostat having first and second stage output signal terminals, the method of using a single input line between the room thermostat and the control comprising the steps of shorting the first and second stage input signal terminals of the control together, taking a diode and connecting the diode between first and second stage output signal terminals of the room thermostat to create separate microcontroller recognizable signals.

2. A method according to claim 1 in which the HVAC system is a cooling system and the room thermostat has Y1 and Y2 two stage cooling signal terminals and the first and second stage output signal terminals of the room thermostat are the Y1 and Y2 terminals.

3. A method according to claim 2 in which the diode has an anode and a cathode, the anode is connected to one of the Y1 and Y2 terminals and the cathode is connected to the other of the Y1 and Y2 terminals, the control being insensitive to diode polarity.

4. A two stage HVAC system comprising a control having a microcontroller and relays, the microcontroller having first and second two stage input signal terminals, a power supply from a transformer rectified to create DC voltages for the microcontroller and relays, a two stage room thermostat having first and second stage output signal terminals and a diode connected between the first and second stage output signal terminals of the room thermostat to create separate microcontroller recognizable signals.

5. A two stage HVAC system according to claim 4 in which the first and second two stage input signal terminals are shorted together.

6. A two stage HVAC system according to claim 5 in which the HVAC system is a cooling system and the room thermostat has Y1 and Y2 two stage cooling signal terminals and the first and second stage output signal terminals of the room thermostat are the Y1 and Y2 terminals.

7. A two stage HVAC system according to claim 6 in which the diode has an anode and a cathode, the anode is connected to the Y1 terminal and the cathode is connected to the Y2 terminal, the control being insensitive to diode polarity.