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Technical Instructions
Document Number 155-327P25
Rev. 1, March, 2002
Set Point Limit Stops
Operating Modes
Normal Mode
Frost Protection Mode
(RCU50U)
Energy Saving Mode
Operating Mode
Changeover Switch
(RCU50U)
Mechanical Design
Page 4
The room temperature set point can be limited in increments of 2°F (1°C) by using the
minimum and maximum set point limit stops. This prevents arbitrary set point
readjustments.
To set limit stops, remove the set point knob by pulling it straight off the shaft.
Reposition gray tabs for high and low stops in the holes around the perimeter of knob
as required. See Figure 6.
When dry contact (D1 and Ground) is open, the set point knob setting takes over
control and normal mode is initiated.
Frost protection mode can be initiated by activating the external operating mode
changeover switch, if DIP Switch No. 1 is set to OFF.
If the room temperature falls below 46°F (8°C), the controller will automatically switch to
frost protection mode. In that case, the heating valve opens and the room temperature
is maintained at a set point of 46°F (8°C). The set point adjusted by the user will be
ignored.
Energy saving mode can be initiated by activating the external operating mode
changeover switch, if DIP Switch No. 1 is set to ON.
In energy saving mode, the heating set point is 61°F (16°C) and the cooling set point is
82°F (28°C), independent of the position of the set point knob.
A changeover switch can be connected to status input D1–GND. When the switch
closes its contact (caused by an open window, for instance), the operating mode
changes from normal operation or standby to energy saving mode (if DIP Switch No. 1
is set to ON), or from normal operation or energy saving mode to standby (if DIP Switch
No. 1 is set to OFF).
The operating action of the switch (N.C. or N.O.) can be selected.
The unit consists of two parts:
• Plastic housing which accommodates the electronics, the operating elements and
the built-in room temperature sensor.
• Controller base.
The housing snaps into the top and bottom of the mounting base.
RCU50U and RCU50.2U Room Temperature Controllers
65
7 0
60
20
75
15
55
25
80
50
10
85 ºF
30
Cº
Figure 6. Set Point Limit Stops.
for CAV Systems
Siemens Building Technologies, Inc.
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