506230−01 05/09
Page 2
IMPORTANT
Read this manual before programming the thermo-
stat.
Use this thermostat only as described in this manual.
WARNING
Always turn off power at the main power source by
switching the circuit breaker to the OFF position be-
fore installing or removing this thermostat.
All wiring must conform to local and national build-
ing and electrical codes and ordinances.
Do not switch system to cool if the outdoor tempera-
ture is below 45°F (7°C). This can damage the cool-
ing system.
ComfortSense
®
Model L7742U Thermostat
(Catalog No. Y2081)
Description
The ComfortSense
®
Model L7742U thermostat is an elec-
tronic 7−day universal multi-stage programmable touch
screen thermostat. It also offers enhanced capabilities
which include:
S humidification measurement and control,
S dew point adjustment control,
S dehumidification measurement and control,
S Humiditrol
®
Enhanced Dehumidification Accessory
(EDA) capability,
S equipment maintenance reminders,
S worry−free memory storage feature,
S menu−driven display.
This thermostat supports heat pump units or non−heat
pump units, with up to 4 stages of heating (dual fuel units)
and 2 stages of cooling.
Dimensions
Screen dimensions: 3−7/16" (87 mm) width x 2−9/16" (65
mm) height
Case dimensions: 5−7/8" (149 mm) width x 4−9/16" (116
mm) height x 1−1/4" (31mm) depth
Features
Compressor Short Cycle Protection
A 5−minute compressor short cycle protection timer begins
when a compressor output is de−energized. Also, if a pow-
er loss occurs, the system will go into compressor protec-
tion mode and display WAIT in the display if there is a cool-
ing or compressor heating call.
Outdoor Temperature Sensor
An outdoor temperature sensor (X2658) is required for
dual fuel applications, balance points, dew point humidity
control, and with Humiditrol
®
EDA.
In addition to measuring and displaying outdoor tempera-
ture, the outdoor sensor provides dew point adjustment
and control for all models. If used with this thermostat, the
sensor enables optimal heating equipment operation via
programmable balance points.
NOTE − The outdoor sensor uses standard thermostat wir-
ing; it may be wired using two wires of a multi−wire cable.
When the outdoor sensor is connected, the temperature
can be displayed in the information display area (see figure
2).
NOTE − For proper operation of Humiditrol
®
EDA applica-
tions, the outdoor sensor (X2658) MUST be installed.
L" Input
L" input from the equipment is used to notify the user of an
outdoor equipment fault by displaying HVAC ERROR DE-
TECTED" when one of the following conditions exist:
S L" terminal is activated with 24VAC and Y1 has been
activated for 5 minutes (units without LSOM, but which
use Service Light Monitor Kit), OR,
S LSOM error signal is detected on L" input and Y1 has
been activated for 5 minutes.
NOTE − The L input is used for diagnostic information pur-
poses only, it is not intended to provide equipment protec-
tion.
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