Installation
• The RTU is normally installed on an interior wall of the main living area of the building. Do not mount the RTU near a heat source
(e.g. sunlight through a window, a fireplace, etc.) or in a drafty area ( e.g. near an exterior door or a window) unless the sensor element
is mounted remotely in a suitable location.
• Remove the front of the RTU by pulling at its top and bottom. Mount the RTU base to the wall or an electrical box using two screws.
• Connect two wires to the RTU terminals labelled “RT RT”. Connect the other end of the wires to the appropriate terminals on the
tekmar heating system controls’ socket. (See the Data brochure of the particular control you are using).
• Set the selector switch in the RTU to “INT” or “EXT”.
— “INT” means that the digital setback timer will enable the dial (setback dial) during setback, and adjusting this dial will affect
the amount of setback there is.
— “EXT” means that the dial is disabled and a wire connected from the RTU terminal “Ti” to the appropriate terminal in the socket
of the tekmar reset or zone control will cause the tekmar control to enter its own internal setback.
• Re-install the cover of the RTU. Set the dial to the 68°F (20°C) setting, and
the dial to its mid-range setting.
Options
• If a remote sensor is desired, away from the RTU’s location, then remove the small
disc shaped sensor from the RTU at the terminals labelled “Sensor”, and install the
remote sensor here. (types 313, 317, 318, 321 or 324)
• If this RTU is to be used as only a setback timer for a tekmar reset control, then
in place of the internal RTU disc shaped sensor, install the 2430Ω resistor from the
reset control and follow the procedure for “EXT” operation. The dial must be
kept in its 68°F (20°C) position.
Programming the Clock of RTU type 308
• When this RTU is first powered up, the clock’s internal battery needs to be charged
and therefore there will be no display for 5-10 minutes. When the display appears,
proceed to program the clock. This setback clock is capable of up to three different
day/setback cycles per day. These times can be the same every day of the week
(24 hr schedule), or can be different every day of the week (7-day schedule).
Notes
• If the “hour” or “min.” button is held for more than 1 second during program-
ming, the displayed time will advance quickly.
• If there is no keypad activity for 40 seconds, program mode is abandoned.
• The terms “setback” and “Daymode OFF” are interchangeable.
1) To reset the clock and clear all programmed information
• Press at the same time “day”, , “min.” and buttons, then release.
2) To set time and date
• Press and hold
• Press “day” then “hour” then “min.” to program the correct time. Release .
2/92
- Data Brochure
The Setback Room Temperature Unit (RTU) type 308 is compatible with all tekmar controls having type numbers from 228 to 245 and
type numbers 251, 252 and 354.
Whenever solar radiation, a fireplace, or any other heat source causes the room temperature to increase, the RTU causes the electronic
control to immediately decrease the amount of heat supplied by the heating system. The RTU also forces the electronic control to overdrive
the heating system for a short interval during heat-up from setback to normal room temperature. This action reduces the time required
to restore normal room temperature.
For mounting instructions, see Data brochure D001. Outside dimensions are 4-1/2" H x 2-3/4" W x 7/8" D, (114 H x 70 W x 22 D mm).
The built-in, self-charging battery will provide up to 1.5 hours of backup in the event of a power failure.
RT RT
Sensor
Ti
Prog.
1➞7
68°F
(20°C)
78°F (25°C)
(15°C) 58°F
None
Setback
Instructions
inside
Selector switch
temperature
indicator
day hour min.
Prog.
1➞7
68°F
(20°C)
78°F (25°C)(15°C) 58°F
None
Setback
Instructions
inside
1234 6751➞7
PM
ON
OFF
Front panel
setback
dial
day temp.
dial
keypad
LCD display
Wiring terminals
Normal (day) adjustment range
Setback adjustment range
61 to 75°F (16 to 24°C)
0 to 12°F (0 to 7°C)
59 to 79°F (15 to 25°C)
0 to 18°F (0 to 10°C)
with reset controls 228 - 245 with zone control 240Feature
with controls 251, 252, 354
61 to 75°F (16 to 24°C)
0 to 12°F (0 to 7°C)
D 06
Setback RTU 308
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