69-0778—1
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QUALITY IS KEY
Operation
The T4798S Thermostat controls the room temperature
to the preset temperature depending on the occupancy and
lighting in the controlled space. The thermostat responds to
the occupancy and light conditions by selecting the preset
temperature for the operating mode. The temperature is
adjusted to maximize both comfort and energy savings.
The SEL key allows selection of one of the four operat-
ing modes. The SET key enters the operating mode, allow-
ing changes to be made. The thermostat liquid crystal
display (LCD) indicates the current operating mode and
setpoint. The room temperature is displayed for ten seconds
by pressing and releasing the SET key.
The light sensing level of the thermostat can be chosen
from one of three conditions:
—L1 indicates most sensitive; thermostat reacts to the
minimum amount of light. This is typically used to
detect artificial lighting or “evening”.
— L2 indicates less sensitive; thermostat reacts to a
little more than the minimum amount of light.
— L3 indicates least sensitive; thermostat reacts to the
highest amount of light. This is typically used to
detect lighting or solar gain. It is useful for rooms that
face west or south.
The thermostat does not require batteries and maintains
the program during a power failure. It is not necessary to
reprogram the thermostat when there is a change in daily
schedule or for daylight savings time.
The microprocessor proportional, integral plus derivative
algorithm controls the duty cycle to accurately maintain the
temperature setpoint during all operating conditions.
NOTE: The T4798S thermostat does not have a clock;
therefore, it does not adjust the room temperature to warm
up the room until the room is occupied. Derivative con-
trol will warm up the space as fast as the heaters can.
The thermostat triac controls electric convectors propor-
tionately to the heating load of the room. The triac cycles
240 times per hour, turning on longer as the load increases.
At this cycle rate, the heating element is always warm
except during warm-up periods when it is hot. This makes
it safer for children who may play near convectors. It also
provides more comfort since the air is always circulating,
which eliminates the dark streak above hot baseboard heat-
ers.
The high cycle rate makes the T4798S uncompatible
with inductive loads such as fans, relays and pumps. The
T4798S is for use only with resistive loads.
NOTE: To minimize room temperature fluctuations, the
thermostat will not change from an occupied to unoccu-
pied mode for 60 minutes (for light) or for three hours
(for dark) when an occupant leaves the controlled space.
This equipment is a Class B digital apparatus which complies with Canadian Radio Interference Regulations, CRC c.1374.
Home and Building Control
Home and Building Control
Helping You Control Your World
Honeywell Inc.
Honeywell Limited—Honeywell Limitée
1985 Douglas Drive North
740 Ellesmere Road
Golden Valley, MN 55422
Scarborough, Ontario
M1P 2V9
Printed in Canada