Heat Pump Controls - Bosch FHP RT-20 Installation, Operation And Maintenance Manual

Heat Pump Controls

Each unit is factory provided with a Unit Protection
Module (UPM) that controls compressor operation
and monitors the safety controls that protect the unit.
The UPM is a printed circuit board and is found in the
heat pump module.
Safety controls include the following:
• High pressure switch located in the refrigerant
discharge line and wired across the HPC terminals
on the UPM
• Low pressure switch located in the unit refrigerant
suction line and wired across terminals LPC1 and
LPC2 on the UPM.
• Optional freeze protection sensor located on
the leaving side of the water coil prevents unit
operation below 35°F or 15°F (depending on dip
switch setting). The freeze dip switch must be set
to "ON".
NOTE
The factory default for the Freeze setting is in "NO"
position. If the freeze stat option is ordered, the
switch must be repositioned to the "YES" position.
• Condensate overflow protection sensor located
in the drain pan of the unit and connected to the
"COND" terminal on the UPM board.
The UPM include the following features:
Anti-Short Cycle Timer
Five minute delay on break timer to prevent
compressor short cycling.
Random Start
Each controller has a unique random start delay
ranging from 270 to 300 seconds to reduce the
chances of multiple units simultaneously starting after
initial power up or after a power interruption, creating
a large electrical spike.
Low Pressure Bypass Timer
The low pressure switch is bypassed for 120 seconds
after compressor start-up to prevent nuisance low
pressure lockouts during cold start-up in the heating
mode. If the low pressure switch remains opened
after 120 seconds, the unit enters a soft lock.
Brownout/Surge/Power Interruption Protection
The brownout protection in the UPM board will shut
down the unit if the incoming power falls below
18 VAC. The unit will remain off until a minimal
incoming power of 18 VAC is detected. Once proper
power is restored, the unit will start up within the
random start time period.
Malfunction Output
The controller has a set of wet contacts for remote
fault indication or dry contacts for communication
with a DDC controller or BMS. The fault output will
depend on the dip switch setting for "ALARM". If set
32 Model RT Energy Recovery Unit
to "CONST", a constant signal will be produced to
indicate a fault has occurred and the unit requires
inspection to determine the type of fault. If it is set to
"PULSE", a pulse signal is produced and a fault code
is detected by a remote device indicating the fault.
See LED Fault Indication for blink code explanations.
The remote device must have a malfunction detection
capability when the UPM board is set to "PULSE".
Test Dip Switch
A test dip switch is provided to reduce all time delay
settings to five seconds during troubleshooting or
verification of unit operation. Note that operation of
the unit while in test mode can lead to accelerated
wear and premature failure of the unit. The "TEST"
switch must be set back to "NO" for normal
operation.
Freeze Sensor
This is optional and can be set to ignore or monitor
a freeze sensor. There are two configurable freeze
points, 35°F and 15°F. The unit will enter a soft
lockout until the temperature climbs above the set
point and the anti-short cycle time delay has expired.
NOTE
If unit is employing a fresh water system (no anti-
freeze protection), it is extremely important to have
the "Freeze" switch set to 35°F in order to shutdown
the unit at the appropriate leaving water temperature
and protect your heat pump from freezing if a freeze
sensor is included.