Honeywell
T841D,E
Heating-Cooling Thermostats
INSTALLATION INSTRUCTIONS
Installation Instructions for the Trained Service Technician.
APPLICATION
T841 Thermostats provide 24 Vac control of multistage
heating and cooling systems using manual changeover.
The T841D controls 1-stage heat and 2-stage cool and the
T841E controls 2-stage gas heat and 1-stage cool. The
T841D,E, provide HEAT-OFF-COOL system switching
and AUTO-ON fan switching.
Test holes are provided on the front of the thermostat to
accommodate test meter probes without removing the
thermostat from the wall. Remove the cover of the
thermostat to expose the test holes, which are labeled to
correspond with terminals on back of the thermostat. See
Fig. 1.
Table 1. Thermostat Features.
Order Number
LEDs
Terminal D esignations
System Switch
Fan Switch
Fig.
T841D
CHECK, HI SPD, LO SPD
R,G,W,B,L,X,Y1,Y2,O
HEAT-OFF-COOL
AUTO-ON
2
T841E
HI, LOW
R,G,W1,B,W2,Y
HEAT-OFF-COOL
AUTO-ON
3
F R O N T O F D E V I C E
B A C K O F D E V I C E
-S Y S T E M SW ITCH
FAN SW ITCH
THERMO METER
SETPOINT
SCALE
- LED (UP
TO THREE)
MOUNTING
H OLES (4)
W IRIN G TERM INAL 1
(UP TO 12)
COVER
Fig. 1. External view of T841.
OPERATION
The T841E stages of heat
make
sequentially as the
temperature drops.
Make
refers to the mercury switch
initiating a call for heat or cool.
There is about 1 °F (0.6°C) between stages so the second
stage (auxiliary heat) makes only when the first stage
cannot handle the load. This 1°F is the
interstage d
i
fferen
tial.
The T841D stages of COOL-ON make sequentially as
the temperature rises.
The light emitting diodes (LED) indicators light on certain
thermostats when something specific happens within the
system. Refer to the following list when the LED lights:
HI: Stage two of heat is operating.
LOW: Stage one of heat is operating.
CHECK: System needs to be checked. See heating
system instructions for specific meaning.
HI SPD: Stage two of cooling is operating.
LO SPD: Stage one of cooling is operating.
LEDs are not field replaceable.
®U.S. Registered Trademark
Copyright © 1997 Honeywell Inc.
A ll R ig h ts R e served
69-1066