Install a Low-Voltage Thermostat

A. Finished-Project Specification

Quantity: one replacement low-voltage thermostat, matched to the documented equipment configuration, mounted level and secure on the existing or corrected wall opening, wired to the labeled terminal designations, configured to the documented equipment type and staging, and verified through fan-only, heating, and cooling calls with all equipment panels installed.

B. Thermostat Replacement Schedule

Item	Target Condition	Verification Method
Equipment configuration	Identified and matched to the replacement thermostat's supported configuration before purchase	Manufacturer documentation comparison
Thermostat circuit power	Verified de-energized before any conductor is disconnected	Low-voltage test meter reading
Conductor labeling	Every conductor labeled by terminal designation before disconnection	Visual confirmation and photograph
Base mounting	Level, secure, and free of pinched conductors	Level check and visual inspection
Terminal wiring	Each conductor connected to its matching documented terminal	Visual confirmation against the labeled record
Configuration	Equipment type, staging, and reversing-valve logic set to match the documented system	Manufacturer configuration menu confirmation
Functional test	Fan-only, heating, and cooling calls verified with equipment panels installed	Observed equipment response

C. Material Takeoff

• Control equipment: one replacement thermostat confirmed compatible with the documented equipment configuration.
• Mounting materials: wall anchors specified by the thermostat manufacturer, batteries if specified by the manufacturer.
• Documentation materials: wire labels, camera or phone camera, Thermostat Replacement Worksheet.
• Air-sealing material: compatible removable material for sealing excessive wall-cavity air leakage at the wire opening, where present.

D. Terminal and Configuration Schedule

Record the manufacturer terminal designation, function, and connected conductor label for each terminal present on the documented system, including the transformer-power terminal (R or Rc/Rh), common terminal (C), heat terminal(s) (W/W1/W2), cool terminal(s) (Y/Y1/Y2), fan terminal (G), reversing-valve terminal (O/B), and any accessory terminal identified during Step E. Do not connect a conductor to a terminal whose designation was not confirmed at the existing installation.

E. Acceptance Standards

Check	Standard
Compatibility	Replacement thermostat manufacturer documentation confirms support for the documented equipment type, staging, heat source, cooling source, and accessory terminals
De-energized circuit	Thermostat circuit power verified absent before conductor disconnection
Labeling	Every conductor labeled by terminal designation, not color, before disconnection
Mounting	Base level, secure to the wall surface, and free of pinched conductors
Wiring	Every conductor connected to its matching documented terminal designation
Configuration	Equipment type, staging, and reversing-valve logic configured to match the documented system
Functional test	Fan-only, heating, and cooling calls produce correct authorized equipment response with no fault condition, with all equipment panels installed

F. Identification, Compatibility, and Scope Confirmation

1. Identify the existing thermostat, equipment type, staging, heat source, cooling source, fan control, reversing-valve logic, accessory terminals, and power method. Record each item on the System Configuration Record before proceeding.
2. Confirm that the replacement thermostat supports the exact equipment and control configuration. Compare the recorded configuration against the replacement thermostat's manufacturer documentation before purchase or installation.
3. Stop work for line-voltage thermostats, proprietary communicating controls, unknown terminals, zoning panels, hydronic controls, or unsupported equipment. Do not proceed with removal until this condition is resolved by the required qualified professional.

G. Shutdown and Circuit Verification

1. Shut down indoor and outdoor equipment using Chapter 2. Apply the full readiness procedure to the equipment serving the documented thermostat circuit.
2. Verify thermostat circuit power is absent. Use the low-voltage test meter at the accessible terminal block before disconnecting any conductor.

H. Documentation and Removal

1. Photograph the existing thermostat and terminal connections. Capture the terminal block with every conductor still connected before labeling begins.
2. Label each conductor by terminal designation rather than relying on color. Apply a wire label to every conductor before disconnecting it.
3. Record unused conductors and cable condition. Note any conductor not connected to the existing thermostat and the general condition of the cable jacket.
4. Remove the thermostat body while preventing wires from falling into the wall. Support the cable at the wall opening throughout removal.
5. Disconnect one conductor at a time and maintain labels. Confirm each label remains legible and attached as the conductor is freed.
6. Remove the old base and inspect the wall opening, cable, drafts, damage, and mounting surface. Record any condition requiring correction before mounting the new base.
7. Seal excessive wall-cavity air leakage using a compatible removable method without damaging conductors. Apply only where airflow is clearly excessive at the opening.

I. New Base Mounting and Wire Preparation

1. Position the new base level or aligned as required by the manufacturer. Use the level to confirm orientation before marking anchor points.
2. Secure the base without pinching or overtightening. Verify the labeled conductors remain free to move through the base opening.
3. Prepare conductors to the required strip length. Strip each conductor to the length specified by the replacement thermostat's manufacturer instructions.

J. Wiring, Configuration, and Mounting

1. Connect each conductor to the matching approved terminal. Use the labeled terminal designation recorded in Step H, not conductor color, to determine each connection.
2. Configure jumpers, switches, equipment type, staging, and reversing-valve logic according to the documented system. Follow the replacement thermostat's manufacturer configuration procedure.
3. Install batteries or common-wire power as specified. Confirm the power method matches what was recorded in the System Configuration Record.
4. Attach the thermostat body. Confirm it seats fully and squarely against the mounted base.

K. Functional Test

1. Restore equipment power. Close the disconnects and breakers opened during Chapter 2 shutdown.
2. Program the basic system configuration. Set the time, schedule, and any required initial setup screens per the manufacturer instructions.
3. Initiate a fan-only call and verify operation. Confirm the indoor blower starts without a heating or cooling call.
4. Initiate a heating call and observe the authorized sequence without opening combustion or electrical compartments. Confirm the equipment responds correctly from outside the closed cabinet.
5. Initiate a cooling call and observe indoor and outdoor response. Confirm both the indoor and outdoor units respond correctly to the call.
6. Verify shutdown after satisfying or canceling each call. Confirm the equipment stops when the call ends.
7. Stop work for blown fuses, short cycling, no response, simultaneous heat and cooling, abnormal noise, or fault codes. Do not continue testing past a fault condition.
8. Re-isolate power before correction. Apply the Chapter 2 procedure again before investigating any fault.
9. Document terminal mapping, configuration, and functional test results. Complete the Thermostat Replacement Worksheet before closing out the project.