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Installation Instructions
Bosch IDS BOVA15 Split System Heat Pump - BTC 761701317 A (02.2022)
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 the unit's pressure transducer. To ensure 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 automatically adjust based on
compressor operation so optimal capacity can be achieved. Target pressure
can be manually adjusted (SW4) to achieve improved dehumidification and
capacity demands.
Figure 38
ON
OFF
1 2 3 4
SW4
Switch
Description
SW4-1
ON
Unused
OFF*
Must be set at "OFF" position
SW4-2
ON
Unused
OFF*
Must be set at "OFF" position
SW4-3
ON
Adaptive capacity output disabled
OFF*
Adaptive capacity output enabled
SW4-4
ON
Accelerated cooling/heating
OFF*
Normally cooling/heating
Table 11
*Factory Default
Adaptive capacity function is a "self-learning function" which allows a
range of target coil temperatures to adapt for better unit operation and
reduced short cycling.
Accelerated cooling/heating function changes the initial target coil
temperature to provide "enhanced comfort" by increasing unit capacity.
15.2 Sensors (Thermistors/Pressure Transducer)
T3 = Outdoor Coil Temperature (Table 15)
—
High/Low temperature protection
—
Outdoor fan control (cooling mode)
—
Defrost control (heating mode)
T4 = Ambient Temperature (Table 15)
—
Operating condition permission
—
Defrosting condition permission
—
Outdoor fan control (heating mode)
T5 = Compressor Discharge Temperature (Table 16)
—
High/Low temperature protection
—
Electronic Expansion Valve (EEV) (ODU/heating mode only)
T3L = Liquid Line Temperature (Table 15)
TF = Control Board Temperature (Table 16)
—
Inverter High Temperature Protection
Pressure transducer
—
Compressor frequency control
—
Electronic Expansion Valve (EEV) control (heating mode only)
—
High pressure protection (heating mode)
—
Low pressure protection (cooling mode)
15.3 Pressure Equalizer Valve (PEV)
Used to balance the pressure in the system before compressor start up.
15.4 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.
Any one of the below three conditions is required to enter defrost:
1.
The calculated temperature diff erence between the outdoor
temperature (T4) and the coil temperature (T3) is called Delta T. After
Delta T is achieved and continues for 3 minutes.
—
T4 ≥ 39°F, Delta T = 21°F
—
T4 ≥ 30°F, Delta T = 19°F
—
T4 ≥ 19°F, Delta T = 17°F
—
When T4 < 19°F, T3 < 9°F, accumulative compressor run
time ≥ 80 minutes.
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.
