Technical Instructions
RAB20 Series Two-pipe Fan Coil Room Thermostat
Document Number 155-526P25
March 2, 2007
Page 2
Siemens Building Technologies, Inc.
Operation
Heating Mode
If the room temperature falls below the selected setpoint, the heating contact is closed.
Cooling Mode
If the room temperature rises over the selected setpoint, the cooling contact is closed.
Fan Speed
The fan control speed can be controlled two ways:
•
Manually, using the three-speed fan switch on the thermostat cover for continuous
operation. (Low), (Medium),
(High).
•
Automatically, by switching to the selected fan speed using the thermostat for
controlled operation. Prior to commissioning, the jumper position corresponding to
the thermostat function must be selected.
There are three jumper position choices on the printed circuit board:
Fan Release Setting
SR1
SR2
SR3
Select fan speed as continuous operation
Auto
Fan is switched with the cooling valve
Auto
Fan is switched with the heating valve
Ventilation
When the ventilation function ( ) is selected (on the RAB20.1.. only), the heating and
cooling contacts are always open and the fan works at the selected speed.
Changeover
Heating/cooling changeover is automatic, based on room temperature. Changeover is
achieved externally using an SPDT aqua sensor (not included) wired between
Terminals W, Y and the zone valve to change switch action.
Adjustments
The required temperature can be selected by a rotating setpoint adjuster on the front of
the thermostat.
High and low setpoint limit stops can be engaged to limit temperature range.
Table 1. Product Numbers.
Mounting Style
Product
Number
Description
RAB20UW
Heating or cooling; degrees Fahrenheit and
Celsius; two-pipe auto changeover
Electrical Wall
Box (with wall
box adapter)
RAB20.1UW Heating or cooling; degrees Fahrenheit and
Celsius; two-pipe auto changeover; fan only
function
RAB20U
Heating or cooling; degrees Fahrenheit and
Celsius; two-pipe auto changeover
Drywall
RAB20.1U
Heating or cooling; degrees Fahrenheit and
Celsius; two-pipe auto changeover; fan only
function
