Installation: 1source S1-THEU21P7S 7 Day Programmable Thermostat Instruction Manual

Content

Overview

The S1-THEU21P7S 7 Day Programmable Thermostat is a system-powered digital control for residential heating and cooling equipment. It is intended for homes and similar applications using compatible 24-volt HVAC systems, including gas, electric, and heat-pump configurations.

Its seven-day programming capability allows each day to follow its own schedule. The backlit display improves visibility in low-light conditions, while the auxiliary heat indicator helps identify when second-stage heat is operating.

Specifications

Model: S1-THEU21P7S
Thermostat type: Seven-day programmable digital thermostat
Power: System powered; a common wire must be connected in every application
System capacity: Up to two heating stages and one cooling stage
Compatible equipment: Residential gas, electric, and heat-pump systems
Display: Backlit digital display
Temperature scale: Fahrenheit or Celsius
Auxiliary heat indication: Supported
Primary terminals: C, R, Y1, W1/O/B, G, and W2

Detailed Description

The thermostat measures room temperature and compares it with the selected heating or cooling setpoint. When the room temperature moves beyond the programmed or manually selected target, the thermostat signals the appropriate HVAC equipment through its connected terminals.

The R terminal supplies system power, while C provides the required common connection for system-powered operation. Y1 controls first-stage cooling or compressor operation. G controls the indoor fan when the HVAC system uses a separate fan connection. W1/O/B supports first-stage heat or the heat-pump reversing valve, depending on the equipment configuration. W2 provides second-stage or auxiliary heat.

For heat-pump installations, the O or B setting determines how the reversing valve is energized. An O configuration energizes the valve for cooling, while a B configuration energizes it for heating. The system must be configured to match the connected heat pump.

During a heat-pump demand, the thermostat can operate the compressor and reversing valve. When additional heat is required, the W2 auxiliary stage can energize. The auxiliary heat indicator identifies this second-stage heating operation.

Safety

Switch off power to the heating and air-conditioning equipment at the main fuse panel before removing the existing thermostat or handling wiring.
A separate breaker may control the furnace or air handler, so verify that the HVAC equipment is completely de-energized.
Do not rely only on the thermostat display or mode setting to confirm that system power is off.
Keep each wire identified during removal. Incorrect terminal connections can cause improper operation or equipment damage.
Use the wiring arrangement that matches the installed HVAC system. Do not apply a heat-pump diagram to a conventional gas or electric system.

Setup and Installation

Remove the Existing Thermostat

Turn off the heating and cooling system at the main electrical panel.
Remove the cover from the old thermostat.
Loosen the screws securing the thermostat base or subbase, then lift it away from the wall.
Disconnect the wires one at a time.
Label each wire with the letter of the terminal from which it was removed. Tape the wire ends temporarily so they do not fall into the wall.

Terminal Connections

The S1-THEU21P7S requires a common wire connected to C in all applications. Use the terminal function rather than wire color when identifying connections.

Y or Y1: Electric cooling or compressor
W, W1, or H: Gas-furnace first-stage heat
W2: Auxiliary or second-stage heat
O: Heat-pump reversing valve energized for cooling
B: Heat-pump reversing valve energized for heating
C: Common connection
R, Rh, M, Vr, or A: System power
G or F: Indoor fan

Supported Wiring Arrangements

The thermostat supports several common residential configurations. A five-wire, one-stage heat-pump system may use O or B for the reversing valve and does not include auxiliary heat. A five-wire conventional system may combine one-stage gas or electric heat with electric cooling. Four-wire arrangements can be used for one-stage heat with a separately controlled fan or for one-stage electric cooling.

A six-wire heat-pump installation can provide one-stage cooling, two-stage heating, a reversing valve, fan control, system power, and the common connection. Confirm the actual equipment design before selecting a wiring arrangement.

Jumper and Equipment Settings

Set the thermostat configuration to match the installed equipment. The available choices distinguish gas or electric operation and heat-pump operation with either an O or B reversing valve. Electric heat and gas heat may require different fan-control behavior, so use the setting appropriate to the furnace, air handler, or heat pump.

In a gas-furnace application, the furnace may control the blower during heating. In electric-heat applications, the thermostat can use the G connection with the heat demand. For heat pumps, select the correct reversing-valve orientation and verify whether auxiliary heat is connected to W2.

Operation

Mode Selection

Use the MODE button to select the available operating state. OFF prevents heating and cooling calls. COOL operates the cooling system when the room temperature rises above the cooling target. HEAT operates the heating system when the room temperature falls below the heating target.

Use the FAN button to select fan behavior. When the Fan On icon is displayed, the indoor fan should run continuously. In an automatic fan setting, the equipment normally controls fan operation during a heating or cooling call.

Temperature Adjustment

Use the WARMER and COOLER buttons to change the active temperature setpoint. The thermostat uses the selected setpoint to determine when to request heating or cooling. The display can be configured to show temperatures in Fahrenheit or Celsius.

When checking operation, set the heating target approximately 10 degrees above the room temperature to create a heating demand. For a cooling test, set the cooling target approximately 10 degrees below room temperature. A blinking Heat or Cool icon indicates an active demand.

Seven-Day Programming

The seven-day schedule is designed for separate daily temperature plans. Program each day around the building’s occupancy pattern, using lower heating or higher cooling targets during unoccupied periods when appropriate. After programming, verify the displayed day, time, mode, and active setpoint before leaving the thermostat in automatic operation.

Test Operation

Place the thermostat in OFF mode with the MODE button.
Select COOL mode and press FAN until the Fan On icon appears. Confirm that the indoor fan runs continuously.
Lower the cooling setpoint to approximately 10 degrees below room temperature. Confirm that the cooling equipment starts and the Cool icon blinks.
Select HEAT mode.
Raise the heating setpoint to approximately 10 degrees above room temperature. Confirm that the heating equipment starts and the Heat icon blinks.
If the system has second-stage strip heat, press WARMER once during a heating demand and verify that the W2 stage energizes.

The compressor lockout feature can delay heating or cooling startup for as long as five minutes. This delay helps protect compressor equipment and should not automatically be treated as a fault.

Troubleshooting

Cooling Does Not Start

Confirm that the thermostat is in COOL mode.
Lower the cooling setpoint below the current room temperature.
Allow up to five minutes for the compressor lockout delay to expire.
Check that the common wire and cooling connection are securely installed.

Heating Does Not Start

Confirm that the thermostat is in HEAT mode.
Raise the heating setpoint above the current room temperature.
Allow the system time to respond before changing settings again.
Check that the common wire and heating connection are securely installed.

Auxiliary Heat Does Not Operate

Verify that the system actually includes a second heating stage.
Confirm that the auxiliary heat wire is connected to W2.
Check that the thermostat equipment configuration permits second-stage heating.
Raise the heating demand enough to request the second stage, then check for the auxiliary heat indication.

Fan Operation Is Incorrect

Check whether the Fan On icon is displayed. If it is displayed, continuous fan operation is expected.
Confirm that the G wire is connected when the HVAC system uses a separately controlled fan.
For gas-furnace systems, remember that the furnace may control the blower during heating rather than the thermostat.

Pros & Cons

Pros

Seven-day programming supports different schedules for each day.
Two-stage heating capability supports auxiliary or second-stage operation.
Compatible wiring options cover conventional gas, electric, and heat-pump systems.
Backlighting improves display visibility in low-light conditions.
Fahrenheit and Celsius display options provide flexible temperature viewing.

Cons

Installation requires careful identification of existing HVAC terminals.
A common wire is required for every application.
Heat-pump installations require correct O or B reversing-valve configuration.
Compressor protection can create a startup delay of up to five minutes.

PDF

Faqs

How do I safely install the S1-THEU21P7S 7 Day Programmable Thermostat?

Turn off power to the heating and air-conditioning system at the main fuse panel or furnace breaker before touching any thermostat wiring. Remove the old thermostat cover and loosen its mounting screws. Disconnect each wire individually, label it with the old terminal letter, and prevent the wires from falling into the wall. Mount the new base, then connect the labeled wires to the matching terminals shown for your HVAC system. A common wire must be connected for this thermostat.

How can I identify the correct wiring terminals on the S1-THEU21P7S?

Match the old thermostat terminal letters and wire functions to the new connector rather than relying only on wire colors. Y or Y1 is used for cooling, G for the fan, R or Rh for 24-volt power, C for common, and W1/O/B for heating or the heat-pump reversing valve. W2 is used for second-stage or auxiliary heat. Because O and B reversing-valve systems operate differently, confirm the equipment type before connecting those terminals.

Is a common wire required for the S1-THEU21P7S thermostat?

Yes. The installation instructions specify that a common wire must be connected in all applications. The common connection provides the required system power for this thermostat and should be connected to the HVAC equipment’s C terminal and the thermostat’s C terminal. Do not assume an unused wire is a common wire; identify it from the existing terminal connection or equipment wiring diagram. Turn off system power before checking or changing any connection.

How do I test heating, cooling, and fan operation after installation?

Place the thermostat in Off mode first, then select Fan On and confirm that the blower runs continuously. Select Heat and raise the set temperature about 10 degrees above room temperature; the heat icon should blink and heating should start. Select Cool and lower the set temperature about 10 degrees below room temperature; the cooling icon should blink. Compressor protection may delay heating or cooling operation for up to five minutes.

Why does the S1-THEU21P7S cooling system not turn on?

First confirm that the thermostat is in Cool mode rather than Off or Heat mode. Check the displayed room temperature and lower the cooling setpoint enough to create a demand for cooling. If the setpoint is already lower than room temperature, wait several minutes because the compressor lockout feature can delay cooling startup for up to five minutes. If the system still does not respond, turn power off and recheck the cooling, power, common, and fan wiring.

Why does the heating system not start when using the S1-THEU21P7S?

Verify that the thermostat is set to Heat and raise the heating setpoint above the current room temperature. If the temperature demand is too small, the system may not energize. Heat-pump systems may also delay operation because of compressor protection. Check that the R, C, and heating or reversing-valve connections match the selected equipment configuration. For two-stage systems, confirm that W2 is connected correctly before testing auxiliary or second-stage heat.

How do I test second-stage or auxiliary heat on this thermostat?

After confirming that normal heating works, place the thermostat in Heat mode and press the Warmer button once to increase the demand. On compatible two-stage heat-pump or electric-strip systems, the W2 circuit should energize and the auxiliary heat indicator may appear. Allow the equipment time to respond, since staging and compressor protection can create a delay. Stop the test if wiring becomes warm, unusual noises occur, or the HVAC system behaves unexpectedly.

How do I switch the S1-THEU21P7S display between Fahrenheit and Celsius?

The S1-THEU21P7S supports Fahrenheit and Celsius temperature display through its configuration settings. Change the temperature scale before creating or checking programmed setpoints so the displayed values are interpreted correctly. After switching scales, verify the room temperature and heating or cooling setpoints. Avoid changing other installer settings unless they match the HVAC equipment, because incorrect system type, reversing-valve, or staging settings can prevent proper heating and cooling operation.