Honeywell T8635L - User Manual

Honeywell T8635L

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1 69-1332—3

USER’S GUIDE

T8635L Microelectronic Communicating

Programmable Thermostat

69-1332-3

Table of Contents

Other manuals for Honeywell T8635L

Installation Instructions20 pages

Questions and Answers:

D
Dana SimmonsAug 31, 2025
Why is my Honeywell Thermostat cooling not working, but the system indicator is on?
- S
  Steven WalkerAug 31, 2025
  If the cooling does not come on, but the system on indicator is displayed on your Honeywell Thermostat, it may be due to a communication issue or incorrect wiring. End and repeat the call for cool. Check the Flash Com OK LED on the W8635 EIM or W8835 while the call is being made. If the Flash Com OK LED does not blink, check communication bus wiring. If the Flash Com OK LED blinks correctly, check that 24 Vac is present at Y1 or W1/Y1 terminal, depending on which EIM is being used. If 24 Vac is not present, check R to Rc and/or Rh connections. If the R to Rc and/or Rh connections are good, replace the W8635 EIM or W8835.
B
Blake WhiteAug 30, 2025
Why is my Honeywell Thermostat heating not working, but the system indicator is on?
- L
  lucas30Aug 30, 2025
  If the heating does not come on, but the system on indicator is displayed on your Honeywell Thermostat, it may be due to a communication issue or incorrect wiring. Try ending the call and repeating it. Check the Flash Com OK LED on the W8835 or W8635 EIM during the call. If it doesn't blink, check the communication bus wiring. If it blinks correctly, check for 24 Vac at the W1 or W1/Y1 terminal, depending on the equipment module. If 24 Vac is absent, check the R to Rh connection. If the connection is good, the W8835 or W8635 EIM may need replacement.
J
Janet WardAug 29, 2025
Why is the outdoor temperature not displayed or incorrect on my Honeywell Thermostat?
- P
  Paul SmithAug 29, 2025
  The outdoor temperature may not be displayed, because the installer did not activate this option or the outdoor sensor is connected incorrectly. No answer.
J
Joshua WardAug 28, 2025
What does “no com” mean on my Honeywell T8635L?
- K
  Kristen GrimesAug 28, 2025
  The “no com” message indicates that the thermostat can't communicate with the equipment interface module at the furnace. Try turning the power off and then on to your furnace. If the problem continues, no answer.
M
Martin WilliamsAug 27, 2025
What does 'wait' mean on my Honeywell T8635L Thermostat, and why isn't cooling or heating starting?
- M
  Megan McdonaldAug 27, 2025
  If “wait” is displayed and the call for Cool (or Heat when used in a heat pump application) has not started on your Honeywell Thermostat, compressor protection is likely active. This feature can be set from 0 to 5 minutes to prevent compressor damage from rapid cycling. Wait until the compressor protection period expires. To bypass this during installation, refer to the Installer System Test section.
P
pmitchellAug 27, 2025
How to fix a Honeywell T8635L when the display does not come on?
- L
  lestersharonAug 27, 2025
  If the Honeywell Thermostat display doesn't come on, the issue is likely a power problem. First, ensure the thermostat is correctly mounted and latched on the wallplate. Then, check the circuit breaker and reset it if it has tripped. Next, verify the fuse in the fuse box and replace it if blown. Also, check that the power switch at the equipment is in the On position. Finally, inspect the wires on terminals 2 and 3 for 24 VAC; replace any broken wires. If power is present, the thermostat may need replacement.
H
Hannah Butler MDAug 25, 2025
What to do if my Honeywell T8635L Thermostat cooling does not come on?
- E
  Emily FerrellAug 26, 2025
  If the cooling isn't working, first, make sure the setpoint is below the room temperature. Second, check that the System selection is set to Cool. Finally, if the cooling setpoint is above room temperature, allow five minutes for the system to respond, during which the thermostat will display “Wait”.
J
jason49Aug 25, 2025
What to do if my Honeywell Thermostat heating does not come on?
- S
  Sarah CruzAug 25, 2025
  If the heating isn't working, first, make sure the setpoint is higher than the room temperature. Second, check that the System selection is set to Heat. Finally, if the heating setpoint is indeed below room temperature, allow five minutes for the system to respond, during which the thermostat will display “Wait”.

Honeywell T8635L Specifications

General

Power Source	Battery or Hardwired
Programmable	Yes
Power Method	Battery or Hardwired
Mounting	Wall Mounted
Color	White
Display	Digital
Temperature Differential	1°F
Control Type	Digital

Summary

Using This Guide

Features

Keyboard and Display Description

Keyboard

Details the physical keys on the thermostat cover and next to the display.

Display

Explains the information shown on the thermostat display screen.

Adaptive Intelligent Recovery Control

Optimum Comfort and Energy Savings

Details how Adaptive Intelligent Recovery™ optimizes comfort and saves energy.

Operating Your Thermostat

Setting System and Fan Keys

Instructions for setting the heating/cooling system and fan modes.

Setting the System Key

How to select Heat, Off, Cool, or Auto system modes.

Setting the Fan Key

How to set the fan to Auto or On operation.

Setting Temporary Temperatures

How to temporarily adjust temperature settings.

Changing Temperature to Temporary Setting Until Next Schedule Period

Temporarily override current schedule until next period.

Changing and Holding Temperature Setting Indefinitely

How to set a permanent temperature hold.

Changing Temperature Setting Until a Designated Day and Period (Vacation Hold)

Setting a temporary hold for a specific duration like vacation.

Using the i (Information) Key

Displaying Outdoor Temperature

How to view the outdoor temperature if sensor is equipped.

Displaying Current Settings

How to check current temperature setpoints and modes.

Filter Indicator

Setting or Resetting Filter Indicator

How to set or reset the filter change reminder.

LED Indicators

Remote Override Temperature Indicator

Indicates when temperature is overridden remotely.

Setting the Clock

Setting Current Day and Time

How to set the current day and time on the thermostat.

Daylight Saving Time

How to adjust the thermostat for Daylight Saving Time.

Programming Your Thermostat

7-Day Program and Operation

Overview of 7-day programming and its four periods.

7-Day Preprogrammed Schedule

Details the default preprogrammed schedule for all days.

Customizing Your Own 7-Day Schedule

Table for planning and customizing a custom 7-day schedule.

Programming the First Day

Steps to begin programming the thermostat's schedule for a day.

Copying a Day

Clearing a Program Period

Troubleshooting

Display Issues

Troubleshooting problems with the thermostat display not showing information.

Temperature Setting Problems

Resolving issues where temperature settings do not change or heating/cooling fails.

System Indicator and Airflow Issues

Diagnosing problems with system indicators, no air from registers, or filter alerts.

Communication and Recovery Timing Issues

Addressing 'no com' errors, zoning delays, and early heat/cool activation.

Warranty

Customer Assistance

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