System Architecture Configuration Summary
The configuration below details Control BASIC code maps to the physical terminals, internal variables, register arrays, and field wiring of the Temco Controls Tstat10 thermostat.
Physical Terminal Wiring Map
Terminal Block Variable Label Connected Device / Field Hardware Wiring Instructions
IN1 ROOM_TEMP Onboard Space Thermistor Internal connection; no field wiring required.
IN2 BUFF_TEMP Buffer Tank Immersion Sensor Land one leg on IN2, loop opposite leg to nearest GND terminal.
IN3 ZONE1_TEMP Zone 1 Space Thermistor Land one leg on IN3, loop opposite leg to nearest GND terminal.
IN4 ZONE2_TEMP Zone 2 Space Thermistor Land one leg on IN4, loop opposite leg to nearest GND terminal.
IN5 CLG_RAD_TEMP Radiant Ceiling Surface Thermistor Land one leg on IN5, loop opposite leg to nearest GND terminal.
OUT1 (Relay) COMP_Y1 Heat Pump Compressor Stage 1 Wire to Contact or Terminal Y1 on the Heat Pump.
OUT2 (Relay) COMP_Y2 Heat Pump Compressor Stage 2 Wire to Contact or Terminal Y2 on the Heat Pump.
OUT3 (Relay) REV_VALVE_O Reversing Valve Changeover Wire to Terminal O (Energizes for active cooling mode).
OUT4 (Relay) RAD_ZONE1 Hydronic Valve Actuator Zone 1 Wire to 24VAC Radiant Actuator or Manifold Zone 1 Valve loop.
OUT5 (Relay) RAD_ZONE2 Hydronic Valve Actuator Zone 2 Wire to 24VAC Radiant Actuator or Manifold Zone 2 Valve loop.
24V Power Input 24VAC Transformer Hot leg Supplies power to the Tstat10 device core.
24C Power Common 24VAC Transformer Common leg Connects back to system common transformer bus.
GND Sensor Ground Shared NTC Sensor Common Bus Central termination ground path for all thermistor legs.
Note: All thermistors wired to IN2, IN3, IN4, and IN5 must be 10K Ohm Type 2 NTC Thermistors (non-polarized). Ensure they are explicitly designated as 10K Type 2 in the T3000 software input properties window.
Physical Outputs & Operational Descriptions
• OUT1 (COMP_Y1) — Heat Pump Compressor Stage 1
• Description: This physical relay handles the primary stage of your heat pump compressor. In heating mode (VAR3 = 1), it fires if the buffer tank temperature (VAR2) falls below 83°F to replenish stored thermal energy. In cooling mode (VAR3 = 2), it fires if the room temperature breaches its 1.5°F deadband AND the tank rises above 58°F.
• Safety Interlocks: Strictly governed by a 5-minute (300 seconds) anti-short cycle delay (VAR5) at the bottom of the program loop to protect the mechanical compressor scroll from head pressure locks.
• OUT2 (COMP_Y2) — Heat Pump Compressor Stage 2
• Description: This physical relay activates the secondary, high-capacity stage of your compressor. It acts as an auxiliary booster when Stage 1 alone cannot fulfill systemic thermal demands. It is programmed with an automatic 15-minute (900 seconds) runtime delay; if Stage 1 runs continuously for 15 minutes without satisfying the space temperature, or if room conditions drop/rise drastically beyond 3.0°F of target, Stage 2 kicks in to assist.
• Safety Interlocks: This output is structurally interlocked to Stage 1. It can never turn on unless OUT1 is already actively running. It is instantly stripped of power if the buffer tank triggers an absolute safety ceiling (105°F in heating mode).
• OUT3 (REV_VALVE_O) — Reversing Valve Changeover (O-Style)
• Description: This physical relay commands the heat pump’s internal refrigerant flow direction changer. Following the industry standard “O” changeover pattern, this output energizes and holds continuously active for the duration of the cooling season (VAR3 = 2). Uncoupling this output from the room thermostat calls prevents unnecessary valve shifting and eliminates structural noise/wear during local cycling events.
• Safety Interlocks: It drops out instantly if the master system mode (VAR3) is flipped to Heating (1) or manual Emergency Off (0).
• OUT4 (RAD_ZONE1) — Hydronic Radiant Actuator Zone 1
• Description: This physical relay drives the 24VAC thermal or motorized valve actuator governing your first zone of radiant floor/ceiling piping. It automatically opens during heating if Zone 1 space temperature (IN3) drops below 69°F. During cooling, it permits chilled water circulation if the space exceeds 75°F.
• Safety Interlocks: Monitored by a dynamic bottom-layer condensation defense check. If the buffer tank temperature drops within 5°F of the onboard calculated room dew point (REG746), this relay is forced open immediately to prevent structural sweating. It is also locked out if the buffer tank drops below 60°F during heating mode.
• OUT5 (RAD_ZONE2) — Hydronic Radiant Actuator Zone 2
• Description: This physical relay operates completely independently from Zone 1 to drive the 24VAC actuator loop for your second hydronic zone. It monitors its own dedicated space sensor (IN4), opening the circuit when heating or cooling thresholds are crossed relative to the primary setpoint.
• Safety Interlocks: Governed by the exact same strict dew point defense constraints and low-temperature tank limits as Zone 1 to ensure system safety without relying on external dry-contact switches.
Internal Variable Allocation Matrix
These registers operate entirely behind the scenes to track deadlines, display properties, and trigger the safety loops configured in your logic code.
• VAR1 (MAIN_SETPT): Active Space Temperature Target Setpoint (LCD Line 1 target display value; SET FROM THE THERMOSTAT).
• VAR2 (BUFF_TEMP_DIS): Live Buffer Tank Temperature Tracker (LCD Line 2 real-time display variable; mirrors IN2).
• VAR3 (SYS_MODE): Master Operational State Controller (User or automated register input: 0 = System Off, 1 = System Heat, 2 = System Cool, SET FROM THERMOSTAT).
• VAR4 (DEW_PT_DIS): Conditional Dew Point Readout (LCD Line 3 real-time variable; displays live psychrometric calculated values from REG746 during cooling operations, or blanks out to 0 when heating).
• VAR5 (AS_TIMER): Compressor Anti-Short Cycle Delay Guard (Counts up continuously in seconds whenever Stage 1 stops; forces an un-overrideable lock if it reads < 300 seconds / 5 minutes).
• VAR6 (STG1_TIMER): Stage 1 Continuous Run Accumulator (Tracks operational duration in seconds; steps up compressor engagement to Stage 2 if Stage 1 stays active for longer than 900 seconds / 15 minutes).
• VAR7 = REG746 (ROOM_DEW): Onboard Hardware Psychrometric Register (Pre-calculated value on the Tstat10 board tracking room dew point; continuously monitored by your condensation defense checks).
LCD Screen Display & Status Icon Array (AY1)
The program utilizes the specialized Tstat10 AY1 system array block to update the on-screen physical layout indicator icons every cycle:
┌───────────────────────────────┐
│ [DAY/NIGHT] [OCC/UNOCC] │ ◄── Managed by AY1[0] & AY1[1]
│ [HEAT/COOL] [FAN STAGE] │ ◄── Managed by AY1[2] & AY1[3]
│ ───────────────────────────── │
│ 70.0°F (MAIN_SETPT / VAR1) │ ◄── LCD LINE 1
│ 87.0°F (BUFF_TEMP / VAR2) │ ◄── LCD LINE 2
│ HEAT (HEAT / COOL / VAR3) │ ◄── LCD LINE 3 (Cooling only)
└───────────────────────────────┘
Array Element Parameters Mapping
• AY1[0] → Day / Night Status
• 1: Locked to DAY Icon visible.
• AY1[1] → Occupancy Status
• 1: Display comes on and shows the OCC (Occupied) Icon visible when active.
• AY1[2] → Operating Mode Status
• 0: Displays COOL Icon (Active when VAR3 = 2).
• 1: Displays HEAT Icon (Active when VAR3 = 1).
• 3: Clears Blank Icon from screen (Active when VAR3 = 0 / Off).
• AY1[3] → Compressor Stage / Fan Windup
• 0: Displays FAN-OFF Status (Both compressor stages idle).
• 1: Displays FAN1 Status (Stage 1 compressor OUT1 is active).
• 2: Displays FAN2 Status (Stage 2 compressor OUT2 is active).
Array Parameters
AY1[0] → DAY or NIGHT 0:NIGHT 1:DAY 3: blank ICON
AY1[1] → OCC or UNOCC 0:UNOCC 1:OCC 3: blank ICON
AY1[2] → HEAT or COOL 0:COOL 1:HEAT 3: blank ICON
AY1[3] → FAN 0: FAN-OFF 1: FAN1 2:FAN2 3:FAN3
Program code example to display specific icons based on program state
10 AY1[0] = 1 'DISPLAYS ARRAY ELEMENT “0” FOR CONDITION 1, “DAY”
10 AY1[1] = 3 'DISPLAYS ARRAY ELEMENT “1” FOR CONDITION 3, “blank ICON”
10 AY1[2] = 1 'DISPLAYS ARRAY ELEMENT “0” FOR CONDITION 1, “HEAT”
10 AY1[3] = 2 'DISPLAYS ARRAY ELEMENT “0” FOR CONDITION 1, “FAN2”
Would you like to review the T3000 register configuration values needed to map the physical buttons on the faceplate so they modify VAR3 or change your default setpoints? Alternatively, we can construct an automatic fallback curve using your inputs. Let me know your preference!
OUT3 locks in and hold continuously as long as the system is switched to Cooling Mode (VAR3 = 2), completely eliminating unnecessary cycling of the heat pump’s changeover valve.