Honeywell CHRONOTHERM IV T8665A User Manual

Honeywell CHRONOTHERM IV T8665A

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1 69-1536–3

USER’S GUIDE

T8665A Chronotherm

®

IV

Wireless Thermostat

69-1536-3

Table of Contents

Questions and Answers:

L
Lisa VaughnJul 30, 2025
Why is my Honeywell CHRONOTHERM IV T8665A Thermostat not turning on heat?
- M
  Mr. Lucas McfarlandJul 30, 2025
  Several factors could be preventing your Honeywell thermostat from turning on the heat. Ensure that the system selection is set to Heat and that the heating setpoint is above the current room temperature. Also, check if the circuit breaker has tripped and reset it if necessary. Inspect the fuse at your fuse box and replace it if blown. Verify that the System switch at the equipment is in the On position. After making these adjustments, allow five minutes for the system to respond, indicated by a “Wait” message on the thermostat.
J
Joshua CoxAug 5, 2025
Why is my Honeywell CHRONOTHERM IV T8665A Thermostat not turning on cooling?
- V
  vsummersAug 5, 2025
  There are a few reasons why your Honeywell thermostat might not be activating the cooling system. First, confirm that the system selection is set to Cool and that the cooling setpoint is below the current room temperature. Additionally, check the circuit breaker and reset it if it has tripped. Examine the fuse at the fuse box and replace it if it's blown. Ensure the System switch at the equipment is in the On position. After these checks, give the system five minutes to respond; the thermostat will display “Wait” during this time.
A
asmithAug 11, 2025
What to do if the Honeywell CHRONOTHERM IV T8665A display does not come on?
- P
  pfullerAug 11, 2025
  If the display on your Honeywell thermostat isn't lighting up, the issue is likely a power problem. Start by checking if the batteries are correctly installed. If the batteries are fine, ensure that the thermostat is properly mounted and latched onto the wallplate. Mount and latch the thermostat securely.
P
Paul MillerAug 17, 2025
What to do if the Honeywell Thermostat temperature setting does not change?
- R
  Robert WelchAug 18, 2025
  If you're unable to adjust the temperature settings on your Honeywell thermostat, it might be because you've reached the upper or lower temperature limits. The acceptable range for heating is 40 to 90°F (4 to 32°C), and for cooling, it's 55 to 99°F (13 to 37°C). Verify that your desired temperature setting falls within these limits.
T
Timothy SmithAug 25, 2025
What if the Honeywell Thermostat indicator is on, but there is no air coming from the registers?
- B
  Brian GlassAug 25, 2025
  If the system on indicator is lit on your Honeywell Thermostat, but no warm or cool air is coming from the registers, it could be that the heating or cooling equipment turns on the fan when the equipment has reached the preset time or temperature. Wait a minute after seeing the or and then check the registers. If there is still no hot or cool air coming from registers, refer to the troubleshooting steps for 'Heating does not come on' or 'Cooling does not come on'.

Honeywell CHRONOTHERM IV T8665A Specifications

General

Power Source	24V AC
Display	LCD
Program Schedule	7-Day Programmable
Stages	1 Heat / 1 Cool
Type	Programmable
Compatibility	Single Stage Heating and Cooling Systems
Terminal Designations	R, W, Y, G
Backup	Battery Backup

Summary

Keyboard and Display Description

Keyboard Layout

Describes the physical keys and their functions on the thermostat.

Thermostat Display Elements

Explains the various icons and information shown on the thermostat display.

Adaptive Intelligent Recovery™ Control

Optimum Comfort and Energy Savings

Explains how the control optimizes comfort and saves energy by pre-heating/cooling.

Operating Your Thermostat

Setting System and Fan Modes

Holding Temperature Settings Indefinitely

Vacation Hold Schedule

Replacing the Batteries

Information Key Usage

Clock and Time Settings

Setting Current Day and Time

Programming Your Thermostat

7-Day Program and Operation

Explains the 7-day programming capability and schedule periods (Wake, Leave, Return, Sleep).

Customizing Your Own 7-Day Schedule

Programming the First Day

Troubleshooting Guide

Common Thermostat Issues and Solutions

Addresses common symptoms like display issues, temperature changes, and heating/cooling problems.

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