Bosch BOVA Series - System Operation and Troubleshooting; Control Logic, Sensors, and Components

Installation Instructions Bosch IDS BOVA | 21
Bosch Thermotechnology Corp. | 12.2016
Data subject to change
15 System operation and troubleshooting
15.1 Control logic description
 The variable speed system adopts the same 24VAC control as any
conventional Heat Pump.
 The compressor’s speed is controlled based on coil pressures monitored
by pressure transducer. To insure stable and adequate capacity, the
compressor speed will modulate relative to evaporator pressure during
cooling operation and relative to condensing pressure during heating
operation. The target pressure can auto-matically adjust based on
compressor operation so optimal capacity can be achieved. Target pressure
can manually be adjusted (SW4) to achieve improved dehumidification and
capacity demands.
ON
OFF
1 2
3 4
6:
Figure 40
Switch Description
SW4-1 Not used
SW4-2 Not used
SW4-3
ON Adaptive capacity output disable
OFF Adaptive capacity output enable
SW4-4
ON Accelerated cooling/heating
OFF Normally cooling/heating
Table 8
15.2 Sensors (thermistors/pressure transducer)
 t3 = Outdoor Coil Temperature (Table 1)
— High/Low temperature protection
— Outdoor fan control (cooling mode)
— Defrost control (heating mode)
— Ambient Temperature forecast
 T4 = Ambient Temperature (Table 1)
— Operating condition permission
— Defrosting condition permission
— Outdoor fan control (heating mode)
 T5 = Compressor Discharge Temperature (Table 2)
— High/Low temperature protection
— Electronic Expansion Valve (EEV) control (ODU)
 TF = IPM Radiator Temperature) (Table 2)
— Inverter High Temperature Protection
 Pressure transducer (Table 3)
— Operating speed control
— Electronic Expansion Valve (EEV) control (ODU)
— High pressure protection (heating mode)
— Low pressure protection (cooling mode)
15.3 Defrost description
 The Demand Defrost Control (DDC) monitors the ODU coil temperature
using thermistor (T3). A second thermistor (T4) monitors outdoor ambient
temperature. Based on these parameters, as well as accumulative run time
and high pressure, the DDC calculates proper initiation of defrost.
 The following three conditions are required to enter defrost:
1. Outdoor coil temperature T3 < 34°F and a corresponding minimum
outdoor ambient temperature is met.
2. After “Minimum Run Time” (MRT) is achieved. MRT is based on outdoor
ambient temperature (T4), for example:
— MRT is 4 hours when: T4 < 23°F
— MRT is 2 hours when: 23°F ≤ T4 < 42°F
3. After the high pressure saturation temperature drops below 82°F for 20
minutes.
 Defrost will terminate once outdoor coil temperature (T3) reaches 64°F for
a period of 1 minute or defrost time has exceeded 8 minutes.
 Defrost Termination Settings (SW5) offers different defrost termination
options for enhanced defrost for different geographical &/or outdoor
conditions.
ON
OFF
1 2
SW5
Figure 41
Defrosting choice SW5-1 SW5-2 Remarks
ON
Operating time is
reduced by 10%
Defrosting extended
for 60 seconds
OFF Normal Normal Default
Remarks
Enter defrost Quit defrost
Table 8