Installation: 1source S1-THEH21P5S Heat Pump Digital Thermostat Instruction Manual

Overview

The S1-THEH21P5S Heat Pump Digital Thermostat is a 5+2 day programmable control designed for residential heat pump systems. It supports one stage of cooling and up to two stages of heating, including auxiliary and emergency heat.

Its backlit digital display helps with operation in low-light conditions, while battery or 24-volt system power provides installation flexibility. The thermostat is intended for homeowners, installers, and service technicians replacing a compatible heat pump thermostat.

Specifications

• Model: S1-THEH21P5S
• System type: Heat pump
• Heating capacity: Up to 2 heat stages
• Cooling capacity: 1 cool stage
• Programming: 5+2 day schedule
• Power: Two AA alkaline batteries or 24-volt system power
• Display: Backlit digital display
• Temperature units: Fahrenheit or Celsius
• Compatible wiring: 18–22 gauge unshielded cable
• Common terminal: C, optional when battery power is used
• Terminals: C, R, Y, W, G, B, and O
• Additional functions: Auxiliary heat indicator, emergency heat, service filter indicator, low-battery indicator, and adjustable dead band

Detailed Description

The S1-THEH21P5S Heat Pump Digital Thermostat controls heating and cooling equipment through a set of low-voltage terminals. The compressor output is connected to Y, the indoor fan to G, and the power connection to R. The reversing-valve connection uses either O or B, depending on whether the equipment energizes the valve during cooling or heating.

The W terminal controls auxiliary heat on systems equipped with a second heating stage. Auxiliary heat can supplement the heat pump during colder conditions, while the emergency heat setting allows the backup heat source to operate without normal heat-pump heating.

The thermostat includes a Mode switch for Heat, Cool, or Off, along with a Fan switch for Auto or On operation. In Auto, the fan runs when the system calls for heating or cooling. In On, the indoor fan operates continuously.

Temperature adjustments are made with the Warmer and Cooler buttons. The programmable design allows separate weekday and weekend schedules, and the thermostat is factory configured to operate one- or two-stage equipment without requiring additional programming for basic operation.

Safety

• Turn off power to the heat pump at the main fuse panel or circuit breaker before removing the old thermostat or connecting wires.
• Follow the installation procedure carefully. If the wiring or equipment type is uncertain, have a qualified technician complete the installation.
• Confirm that the heating and cooling equipment operates correctly before beginning thermostat replacement.
• Replace both AA alkaline batteries at least every 12 months. Replace them immediately when the low-battery indicator appears.
• Annual battery replacement is especially important in areas where freezing temperatures could prevent the heating system from starting.
• Keep the insulating label on the backplate in place. It helps block drafts from inside the wall that could cause inaccurate room-temperature readings.

Setup and Installation

Required Tools

• Flat-blade screwdriver
• Wire cutter and stripper

Remove the Existing Thermostat

1. Switch off power to the heat pump at the main fuse panel or circuit breaker.
2. Remove the cover from the existing thermostat. Check for retaining screws if the cover does not release easily.
3. Loosen the screws securing the thermostat base or subbase to the wall.
4. Disconnect each wire individually. Mark every wire with the terminal letter from the old thermostat before removing it.
5. Tape the disconnected wires to prevent them from falling into the wall.
6. Keep the old thermostat available until the new installation has been tested successfully.

Mount and Connect the Thermostat

1. Feed the wires through the openings in the backplate insulating label.
2. Mount the backplate without tightening the screws excessively. An uneven wall or over-tightened screw can make the slide switches difficult to move.
3. Connect the wires to the matching terminals on the new thermostat.
4. Use the equipment wiring and terminal labels to confirm the correct reversing-valve connection.
5. Install the two AA alkaline batteries even when a 24-volt common wire is connected. The batteries can keep the clock operating during a power interruption.
6. Restore power to the heat pump after all wiring is secured.

Terminal Guide

• C: Common connection; optional when the thermostat uses batteries.
• R: 24-volt power.
• Y: Compressor and cooling output.
• W: Auxiliary heat output.
• G: Indoor fan output.
• B: Reversing valve energized for heating.
• O: Reversing valve energized for cooling.

Typical four-wire installations use power, compressor, fan, and one reversing-valve connection. Five-wire installations add auxiliary heat. The common wire is optional in the configurations described by the installation instructions when two AA batteries are installed.

Replace the Batteries

1. Press down on the battery cover at the front of the thermostat.
2. Pull the cover outward to expose the battery slot.
3. Remove both depleted batteries.
4. Insert two new AA alkaline batteries in the indicated orientation.
5. Engage the bottom hook of the cover with the slot, then snap the cover closed.

The thermostat displays a low-battery icon when replacement is needed. Do not rely on exhausted batteries, even if the thermostat is connected to 24-volt power.

Test Heating

1. Set the Mode switch to Heat.
2. Use the Warmer button to set the target temperature approximately 10 degrees above the current room temperature.
3. Confirm that the heat pump starts.
4. Allow for a possible compressor delay of up to five minutes. First-stage heating also has a two-minute minimum run time.
5. Move the Auxiliary Heat switch to Normal and confirm that the auxiliary heat indicator appears when auxiliary heat is energized.

Test Cooling

1. Set the Mode switch to Cool.
2. Use the Cooler button to set the target temperature approximately 10 degrees below the current room temperature.
3. Confirm that the cooling system starts.
4. Allow up to five minutes for the compressor lockout delay before concluding that cooling has failed to start.

Test the Fan

1. Set the Mode switch to Off.
2. Move the Fan switch to On.
3. Verify that the indoor fan runs continuously.
4. Return the Fan switch to Auto for normal demand-controlled operation.

Auxiliary and Emergency Heat

Auxiliary heat is the second heating stage. It is energized when the room temperature falls sufficiently below the heating setpoint after the first-stage dead band has been reached. The first-stage dead band is adjustable from 1 to 6 degrees, while the second-stage heating dead band is 2 degrees.

Use the Normal position for ordinary automatic operation. The Emergency position bypasses normal heat-pump heating and operates the backup heat source. The Auxiliary Heat indicator shows when auxiliary heat has been energized.

Troubleshooting

Slide Switches Are Difficult to Move

Possible cause: The backplate is mounted too tightly against an uneven wall.

Solution: Slightly loosen the mounting screws and check whether the switches move normally.

Cooling Does Not Start

Possible causes: The cooling setpoint is too high, the Mode switch is not set to Cool, the batteries are weak, or the Auxiliary Heat switch is in Emergency.

Solution: Lower the cooling setpoint, select Cool, replace both batteries, and return the Auxiliary Heat switch to Normal. Also allow up to five minutes for compressor protection delay.

The Fan Does Not Run with the Compressor

Possible cause: The Fan switch is not fully in the Auto or On position.

Solution: Move the switch firmly into the desired position and verify that the fan operates.

Heating Does Not Start

Possible causes: The heating setpoint is too low, the Mode switch is not set to Heat, the batteries are weak, or the Auxiliary Heat switch is in Emergency.

Solution: Raise the heating setpoint, select Heat, replace the batteries, and return the Auxiliary Heat switch to Normal.

Auxiliary Heat Does Not Operate

Possible cause: The Auxiliary Heat switch is set to Lockout.

Solution: Move the switch to Normal and verify that the auxiliary heat indicator appears when second-stage heating is called.

Warranty

The thermostat includes a one-year limited warranty against defects in materials and workmanship. Coverage applies to the original installation location and begins from the date of original installation.

Under the stated warranty terms, a defective part may be replaced with a new or remanufactured part at the manufacturer’s option. Labor and other costs associated with diagnosis, removal, installation, shipping, servicing, or handling are not included.

The warranty excludes normal maintenance, incorrect installation, misuse, unauthorized alteration, improper servicing, electrical-service problems, damage caused by floods, fire, lightning, accidents, corrosive environments, unsuitable parts, and other conditions outside the manufacturer’s control. Energy or fuel costs and indirect or consequential damages are also excluded where permitted by law.

Pros & Cons

Pros

• Supports up to two heating stages and one cooling stage.
• Works with battery power or 24-volt system power.
• Provides auxiliary heat and emergency heat controls.
• Includes a readable backlit display and Fahrenheit/Celsius selection.
• Offers 5+2 day programming for separate weekday and weekend schedules.
• Includes low-battery and service-filter indicators.

Cons

• Requires two AA alkaline batteries even when system power is available for backup clock operation.
• Incorrect O or B reversing-valve wiring can prevent proper heat-pump operation.
• Compressor protection delays can make heating or cooling appear inactive for several minutes.
• The warranty does not cover installation labor or many service-related costs.

Correct wiring, annual battery replacement, and functional heating, cooling, and fan tests are the key steps for dependable operation of the S1-THEH21P5S Heat Pump Digital Thermostat.