Specifications

MICROPROCESSOR FEATURES AND OPERATION
Roth’s geothermal heat pump controls provide
a unique modular approach for controlling
heat pump operation. The control system
uses one, two, or three printed circuit boards,
depending upon the features of a particular
unit. This approach simplies installation and
troubleshooting, and also eliminates features that
are not applicable for some units.
A microprocessor-based printed circuit board
controls the inputs to the unit as well as outputs
for status mode, faults, and diagnostics. A
status LED and an LED for each fault is provided
for diagnostics. An ECM control module
provides eld selectable options for airow and
dehumidication mode, plus an LED to indicate
CFM (100 CFM per ash). If the combination
unit is desired (combination water-to-air and
water-to-water heat pump), a third board
controls the hydronic portion of the unit,
allowing eld selectable hot water/forced air
priority and other options.
Removable low voltage terminal strips provide all
necessary terminals for eld connections. Not only
are the thermostat inputs included, but there are
also two additional removable terminal strips for
all of the accessory and electric heat wiring for
ease of installation and troubleshooting.
Startup/Random Start
The unit will not operate until all the inputs
and safety controls are checked for normal
conditions. At rst power-up, the compressor is
energized after a ve minute delay. In addition,
a zero to sixty second random start delay is
added at rst power-up to avoid multiple units
from being energized at the same time.
Short Cycle Protection
A built-in ve minute anti-short cycle timer
provides short cycle protection of the compressor.
Component Sequencing Delays
Components are sequenced and delayed for
optimum space conditioning performance and
to make any startup noise less noticeable.
Test Mode
The microprocessor control allows the
technician to shorten most timing delays for
faster diagnostics by changing the position of a
jumper located on the lockout board.
Water Solenoid Valve Connections
Two accessory relay outputs at the terminal
strip provide a eld connection for two types
of water solenoid valves, a standard 24VAC
solenoid valve, or a 24VAC solenoid valve
with an end switch. Additional eld wiring is no
longer required for operation of the end switch.
Humidier/Dehumidication Connections
Connections for a humidistat are provided,
which automatically engages the fan when
the humidistat contact closes. In addition, a
eld connection is provided at the terminal
strip for external control of the On Demand
Dehumidication (ODD) feature for the variable
speed ECM motor (when equipped), which
automatically lowers the fan speed when the
space humidity is higher than set point. Either
connection may be used with a thermostat that
includes humidier/dehumidication outputs.
Not applicable for splits/water-to-water.
Airow Monitor (Units with ECM Motor)
An LED on the ECM control module ashes
one time per 100 CFM when the unit’s fan is
operating to indicate airow.
Resistance Heat Control
The electric heat control module contains the
appropriate high-voltage control relays. Low
voltage control signals from the compressor
section energize the relays in the electric heat
module to engage backup electric heat
when necessary.
Electronic Condensate Overow Protection
The control board utilizes an impedance
sensing liquid sensor at the top of the drain pan.
Since the drain pan is grounded, when water
touches the sensor for 30 continuous seconds,
the sensor sends a ground signal to the lockout
board, indicating that a condensate overow
fault has occurred.
19
RXT Series Catalog - August 2010 Roth
Controls