Honeywell T874R User Manual

Honeywell
T874R Thermostats and Q674L Subbases
Installation Instructions for the Trained Service Technician.
TRADELINE•
INSTALLATION INSTRUCTIONS
APPLICATION
The T874R Thermostat and Q674L Subbase provide 24 to 30 Vac control of 2-stage heating and 1-stage cool-ing heat
pump systems with manual changeover. Q674L Subbase provides EM.HT.-HEAT-OFF-COOL system switching and
AUTO-ON fan switching. See Table 1 for specific T874R/Q674L combinations.
Table 1. Thermostat/Subbase Specifications.
Thermostat/
Subbase
Package
Thermostat/
Subbase
Model
Numbers
LED
Indication Changeover Comments
See
Fig.
Y594R1243 T874R1152/
Q674L1207
AUX.HT.,
EM. HT.
Manual Cool
TRADELINE®; adjustable stage 2
heat anticipation. Fixed anticipation
in stage 1. Auto fan in EM.HT.
6
Y594R1300 T874R1475/
Q674L1520
AUX.HT.,
EM. HT.a
Manual Heat
or Cool
TRADELINE®; fixed heat
anticipation. Auto fan in EM.HT.
7
Y594R1425 T874R1616/
Q674L1587
AUX.HT.,
EM. HT.,
CHECK
Manual Heat
or Cool
SUPER TRADELINE®; fixed heat
anticipation. Factory installed jumper
across W1 and Y1. Auto fan in
EM.HT.
8
Y594R1615 T874R1822/
Q674L1710
AUX.HT.,
EM. HT.,
CHECK
Manual Heat
or Cool
TRADELINE®; fixed heat
anticipation. Auto fan in EM.HT.
10
Y594R1664 T874R1871/
Q674L1736
EM. HT. Manual Cool
TRADELINE®; exact replacement
for York model no. 2TH11702224.
9
Y594R1672 T874R1889/
Q674L1736
EM. HT. Manual Cool
TRADELINE®; exact replacement
for York model nos. 2TH11702324
and 6TH11702224.
11
Y594R1698b
T874R1905/
Q674L1777
EM. HT. Manual Cool
TRADELINE®; exact replacement
for York model nos. 2TH11702324
and 6TH11702224. Includes
C815A1054 Outdoor Thermistor.
11
Y594R1706b
T874R1913/
Q674L1777
EM. HT. Manual Cool
TRADELINE®; exact replacement
for York model no. 2TH11702224.
9
Y594R1763 T874R1954/
Q674L1827
AUX.HT.,
EM. HT.a
Manual Cool Requires C815A Outdoor Thermister
for outdoor reset. Fixed stage 1 heat
anticipation. No heat anticipation in
stage 2 heat. Auto fan in EM.HT.
Replaces Y594R1136.
5
Y594R1797 T874R1988/
Q674L1868
AUX.HT.,
EM.HT.
Manual Heat
or Cool
TRADELINE®
12
a EM.HT. LED also shows compressor malfunction.
b Premier White® color.
®U.S. Registered Trademark
Copyright © 1997 Honeywell Inc.
All Rights Reserved
69-0392-9

Honeywell T874R Specifications

General

Compatibility	Electric Baseboard, Convector, and Fan-forced Heaters
Mounting	Wall Mounted
Switching Action	SPST
Display	Digital
Voltage Rating	24V AC

Summary

Application Overview

Operation and Installation Basics

System Operation Details

Explains thermostat operation, stages of heat/cool, and LED indicator functions.

Important Safety Precautions

Details critical safety warnings for electrical shock, equipment damage, and proper handling.

Thermostat Location Guidelines

Provides advice on selecting an optimal installation location for accurate temperature sensing.

Subbase Mounting Procedures

Instructions for mounting the subbase on outlet boxes or walls, including leveling.

Detailed Installation Steps

Pre-Installation Checks

Essential installer checks before starting, including reading instructions and verifying qualifications.

Subbase Mounting

Step-by-step guide for mounting the subbase on various surfaces like outlet boxes or walls.

Subbase Wiring

Comprehensive instructions for connecting system wires to the subbase terminals.

Wiring Diagrams and Schematics

Y594R1763 Wiring Diagram

Internal schematic and wiring for model Y594R1763, including system component connections.

Y594R1243 Wiring Diagram

Internal schematic and wiring for model Y594R1243, detailing heat pump system connections.

Y594R1300 Wiring Diagram

Internal schematic and wiring for model Y594R1300, featuring fixed anticipation.

Y594R1425 Wiring Diagram

Internal schematic and wiring for model Y594R1425, for universal heat/cool systems.

Y594R1664 and Y594R1706 Wiring

Wiring diagrams for Y594R1664 and Y594R1706, replacements for specific York models.

Y594R1615 Wiring Diagram

Internal schematic and wiring for Y594R1615, for systems with un-jumped W2/E terminals.

Y594R1672 and Y594R1698 Wiring

Wiring diagrams for Y594R1672 and Y594R1698, exact replacements for York models.

Y594R1797 Wiring Diagram

Internal schematic and wiring diagram for Y594R1797.

Thermostat Mounting and Settings

Mounting the Thermostat

Step-by-step instructions for attaching the thermostat to the subbase, including cover removal.

Heat Anticipator Adjustment

Procedure for setting the adjustable heat anticipator for 2-stage heating systems.

Setpoint Adjustment

How to adjust the setpoint lever for desired heating and cooling temperatures.

Subbase System and Fan Settings

Guide to using the system and fan switches on the subbase for controlling operation modes.

System Checkout and Calibration

Checkout Procedure

Steps to verify proper operation of heating, cooling, emergency heat, and fan.

Thermostat Calibration

Information that thermostats are factory calibrated and no field calibration is provided.

Thermometer Adjustment

Instructions for adjusting the thermostat's internal thermometer if it deviates from accurate readings.