Installation: 1source S1-THEH21NS Non-Programmable Heat Pump Digital Thermostat Owner Manual

Overview

The S1-THEH21NS Non-Programmable Heat Pump Digital Thermostat is designed for residential heat pump systems that require simple manual temperature control. It supports one stage of cooling and either one or two stages of heating, including systems equipped with auxiliary heat.

This thermostat can operate from a 24-volt HVAC system or two AA alkaline batteries. Its front-panel switches provide direct control of heating, cooling, fan operation, auxiliary heat, and emergency heat.

Specifications

• Model: S1-THEH21NS
• Thermostat type: Non-programmable digital heat pump thermostat
• System capacity: Up to two stages of heat and one stage of cooling
• Compatible equipment: Most one-heat/one-cool and two-heat/one-cool heat pump systems
• Power options: 24-volt system power or two AA alkaline batteries
• Temperature scale: Fahrenheit or Celsius
• Auxiliary heat: Normal, Lockout, and Emergency selections
• Fan control: Auto or continuous On
• Wiring: Terminal connections for common, power, compressor, auxiliary heat, fan, and reversing-valve circuits

Detailed Description

The S1-THEH21NS uses a large digital display to show the current room temperature or the selected temperature setpoint. Pressing the COOLER or WARMER button temporarily changes the display to the desired set temperature. The display returns to the room temperature after the adjustment.

The front panel includes a Mode switch with Cool, Off, and Heat positions; a Fan switch with Auto and On positions; and an Aux Heat switch with Normal, Lockout, and Emergency settings. A flashing Heat or Cool indicator shows when the corresponding equipment is energized. The Aux Heat indicator appears when supplemental heat is operating.

In normal two-stage heating, the heat pump handles the initial demand. Auxiliary heat can be brought on when additional capacity is needed. The thermostat uses a one-degree first-stage deadband and a two-degree second-stage deadband, neither of which is adjustable.

Safety

• Disconnect electrical power to the heater and air conditioner before removing the old thermostat or installing the new one.
• Follow the installation sequence carefully. If any wiring or installation step is uncertain, use a qualified HVAC technician.
• Install two AA alkaline batteries even when the thermostat is connected to 24-volt power. They provide backup operation.
• Replace the batteries immediately when the Low Battery icon appears and replace them at least every 12 months.
• Annual battery replacement is particularly important in areas where freezing temperatures could prevent the heating system from starting if the batteries are exhausted.
• The thermostat complies with applicable FCC Part 15 operating conditions. It must not cause harmful interference and must accept received interference, including interference that may affect operation.

Setup and Installation

Tools and preparation

Installation requires a flat-blade screwdriver and a wire cutter or stripper. Confirm that the heat pump is operating correctly before replacing the thermostat. Turn off power to the heat pump at the main fuse panel.

Remove the old thermostat

1. Remove the cover from the existing thermostat. Check for retaining screws if the cover does not lift away easily.
2. Loosen the screws securing the thermostat base or subbase to the wall.
3. Lift the thermostat away and disconnect the wires.
4. Label each wire with the terminal letter from the old thermostat as it is removed.
5. Keep the old thermostat available for reference until the new installation has been tested.

Wire connections

Terminal labels can vary between thermostats. Match each wire by its original function rather than relying only on wire color.

• C: Optional common connection
• R: 24-volt power
• Y: Compressor or cooling output
• W: Auxiliary heat output
• G: Indoor fan output
• B: Reversing valve energized for heating
• O: Reversing valve energized for cooling

The thermostat supports 18- to 22-gauge unshielded cable in the illustrated heat pump applications. Depending on the equipment, the installation may use four or five conductors. The common wire is optional; when it is not connected, the thermostat must use two AA alkaline batteries.

Do not remove the thermal insulating label on the backplate. Feed the wires through its provided slots so air from inside the wall does not affect room-temperature readings.

Battery installation

Open the front battery compartment by pressing down on the battery cover and pulling it outward. Remove the old batteries and install two new AA alkaline batteries in the indicated orientation. Insert the bottom hook of the cover into its slot, then press the cover closed until it snaps into place.

Normal Operation

1. Move the Mode switch to Heat or Cool.
2. Set the Fan switch to Auto for normal operation. The fan will run when the system calls for heating or cooling.
3. Select On if continuous indoor fan operation is desired.
4. Press WARMER to raise the set temperature or COOLER to lower it.

Select Off when neither heating nor cooling is required. The display shows the current room temperature during normal operation, while the setpoint appears during temperature adjustment.

Auxiliary and Emergency Heat

Normal

In the Normal position, auxiliary heat is available when required to satisfy the heating demand along with the heat pump.

Lockout

In the Lockout position, auxiliary heat is prevented from operating regardless of the heating demand. This setting may be used when supplemental heat is intentionally unavailable.

Emergency

Emergency mode disables compressor functions and energizes only the auxiliary heat source for heating. During cooling operation, the compressor also remains locked out when the Aux Heat switch is set to Emergency. Use this mode only when the heat pump compressor should not operate.

Switching Between Fahrenheit and Celsius

1. Move the Mode switch to Off.
2. Press and hold the COOLER and WARMER buttons at the same time.
3. Release the buttons when the temperature changes to Celsius.
4. Repeat the same button operation to return the display to Fahrenheit.

Test Operation

Heating test

1. Restore power to the heat pump.
2. Set the Mode switch to Heat.
3. Adjust the set temperature to approximately 10 degrees above the room temperature.
4. Confirm that the heat pump begins heating.
5. Set the Aux Heat switch to Normal and check that the auxiliary heat indicator appears when second-stage heat is energized.

The compressor may take up to five minutes to start because of the compressor lockout feature. The first heating stage has a minimum two-minute run time.

Cooling test

1. Set the Mode switch to Cool.
2. Adjust the set temperature to approximately 10 degrees below the room temperature.
3. Confirm that the heat pump begins cooling.

Cooling may also be delayed for up to five minutes by the compressor lockout feature.

Fan test

1. Move the Mode switch to Off.
2. Set the Fan switch to On.
3. Confirm that the indoor fan runs continuously.

Battery Replacement

Replace the batteries as soon as the Low Battery icon appears. Use two AA alkaline batteries. Even when 24-volt system power is connected, keeping fresh batteries installed helps maintain reliable thermostat operation during power interruptions or other system conditions.

Troubleshooting

Cooling does not start

• Lower the cooling setpoint below the current room temperature.
• Confirm that the Mode switch is set to Cool.
• Replace weak or exhausted batteries.
• Move the Aux Heat switch from Emergency to Normal.
• Allow up to five minutes for compressor protection to end.

Heating does not start

• Raise the heating setpoint above the current room temperature.
• Confirm that the Mode switch is set to Heat.
• Replace the batteries if the Low Battery icon is displayed.
• Move the Aux Heat switch from Emergency to Normal when normal heat pump operation is required.
• Allow the compressor protection delay to expire.

Auxiliary heat does not operate

Check that the Aux Heat switch is set to Normal. Auxiliary heat will not energize when the switch is in Lockout. The auxiliary heat indicator should appear when the thermostat calls for second-stage heat.

Fan does not run

Move the Fan switch firmly into either the Auto or On position. In Auto, the fan runs only with a heating or cooling demand; in On, it runs continuously.

Switches are difficult to move

The thermostat backplate may be tightened against an uneven wall. Loosen the mounting screws slightly so the backplate is not distorted.

Warranty

The product includes a one-year limited warranty against defects in materials and workmanship, measured from the original installation date. The remedy may consist of a new or remanufactured replacement part at the manufacturer’s option, subject to the warranty conditions.

The warranty does not cover labor or other costs associated with diagnosis, removal, installation, shipping, servicing, or handling. It applies only at the original installation location and becomes void after reinstallation.

Coverage excludes normal maintenance, improper installation or operation, misuse, unauthorized alterations, electrical-service problems, damage from environmental events or accidents, non-approved parts, certain installation locations, energy costs, and special or consequential damage. Replacement parts receive only the remaining portion of the original warranty period.

Pros and Cons

Pros

• Supports up to two stages of heat and one stage of cooling.
• Works with either 24-volt system power or two AA alkaline batteries.
• Includes auxiliary heat lockout and emergency heat selections.
• Provides a low-battery warning and front-access battery compartment.
• Allows Fahrenheit or Celsius temperature display.
• Uses straightforward switches and buttons for non-programmable control.

Cons

• It does not provide programmable scheduling.
• Auxiliary heat and emergency operation require manual switch selection.
• Battery replacement remains necessary at least annually for dependable backup operation.
• The installation requires careful identification of existing heat pump wiring and reversing-valve configuration.

For basic manual control of a compatible heat pump system, the S1-THEH21NS Non-Programmable Heat Pump Digital Thermostat combines simple operation with support for auxiliary and emergency heating.