Honeywell T8401C User Manual

PRODUCT DATA
® U.S. Registered Trademark
Copyright © 2001 Honeywell • All Rights Reserved
68- 0180- 3
T8400C, T8401C and T8424C,D
Electronic Thermostats
APPLICATION
The T8400C and T8401C Standard Electronic Thermostats
provide single-stage, non-programmable temperature control
for 24V heating-cooling systems with manual changeover
from heat to cool.
The T8424C Electronic Multistage Thermostat provides two-
stage heat and one-stage cool control.
The T8424D Electronic Multistage Thermostat provides two-
stage heat and two-stage cool control.
FEATURES
• Attractive styling complements any decor to the
homeowner’s delight.
• Ease-of-use means fewer homeowner questions and
increased homeowner satisfaction.
• Large display for quick easy readability.
• Conveniently sized 3-1/2 x 3-1/2 thermostat with
optional decorator cover plates (3-7/8 in. x 3-7/8 in. and
5-3/4 in. x 5-3/4 in.) makes it easy to install in a variety
of locations.
• Keys are located for easy access.
• Fan and system switches are located on the lower
edge to eliminate accidental setting changes.
• Easy installation, setup and self-test saves time and
increases installer productivity.
• Manual changeover from heat to cool eliminates
unexpected system operation.
• °F or °C temperature display for added model
flexibility.
• Selectable heating cycle rate (1, 3, 4, 5, 6 or 9, 12 cph)
for a variety of applications which reduces the amount
of inventory.
• Cooling cycle rate is fixed (3 cph), the standard setting
for compressors, for speedy installation.
• Setpoints are permanently held in memory (no
batteries used) and retained during power outages for
increased installer and homeowner convenience.
• Power stealing and hard wired models available for
virtually all equipment and application needs including
gravity or radiating systems, hydronic heat,
condensing gas furnaces, gas or oil forced air and
electric heat.
T8400C and
T8401C
T8424C,D
Contents
Application ........................................................................ 1
Features ........................................................................... 1
Specifications ................................................................... 2
Ordering Information ........................................................ 2
Installation ........................................................................ 3
Settings and Adjustments ................................................. 8
Operation .......................................................................... 10
Checkout .......................................................................... 12
Troubleshooting ................................................................ 13

Honeywell T8401C Specifications

General

Voltage	24V
Programmable	Yes
Backup Battery	No
Mounting	Wall
Switch Type	SPST
Power Source	Hardwired
Display	LCD
Accuracy	±1°F (±0.5°C)

Summary

Features

Application

T8400C and T8401C Standard Thermostats

Controls 24V heating-cooling systems with manual changeover.

T8424C Electronic Multistage Thermostat

Provides two-stage heat and one-stage cool control.

T8424D Electronic Multistage Thermostat

Provides two-stage heat and two-stage cool control.

Specifications

Installation

Installation Overview and Safety

General instructions, cautions, and mercury notice for product installation.

Location Guidelines

Proper placement guidelines for thermostat installation to ensure accurate readings.

Mounting Wallplate and Cover Plate

Instructions for attaching the wallplate and optional decorator cover plate to the wall.

Wiring Guidelines

Procedures and restrictions for wiring the thermostat, including wire gauge and diagram references.

Mounting Thermostat to Wallplate

Steps to physically attach the thermostat unit to the installed wallplate securely.

Setting Fan and System Switches

How to configure the fan and system mode (Heat, Cool, Off) using the thermostat switches.

Setting Temperature Setpoint

Adjusting the desired room temperature using the thermostat's up/down keys.

Setting °F/°C and Heat Cycle Rate

Configuring temperature units and heating cycle rates via installer setup.

Operation

Zero Droop Performance

Explanation of precise temperature control that eliminates room temperature fluctuations.

Power Stealing Technology

Details on how the T8400C draws minimal power from the system for operation.

Energy Savings Tips

Recommendations for reducing energy consumption by adjusting temperature settings.

Sequence of Operations

How the thermostat controls heating, cooling, and fan based on settings and calls.

Fan Control Settings

Operating the fan continuously (ON) or automatically with the system (AUTO).

Heating and Cooling Modes

How the thermostat manages heating and cooling cycles based on system switch settings.

Minimum Off-Timer

Protection feature preventing rapid cycling of the cooling compressor.

Checkout Procedures

Heating System Checkout

Procedure to verify the thermostat controls the heating equipment correctly.

Cooling System Checkout

Procedure to verify the thermostat controls the cooling equipment correctly.

Fan System Checkout

Procedure to verify the thermostat controls the fan operation correctly.

Troubleshooting