System Operation And Troubleshooting; Control Logic Description; Sensors (Thermistors/Pressure Transducer); Pressure Equalizer Valve (Pev) - Bosch IDS BOVA15 Installation Instructions Manual

Installation Instructions

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.
SW4
ON
1 2 3 4
OFF
Figure 38
Switch
ON
SW4-1
OFF*
ON
SW4-2
OFF*
ON
SW4-3
OFF*
ON
SW4-4
OFF*
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.
2 2 |
Description
Unused
Must be set at "OFF" position
Unused
Must be set at "OFF" position
Adaptive capacity output disabled
Adaptive capacity output enabled
Accelerated cooling/heating
Normally cooling/heating

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.
Bosch IDS BOVA15 Split System Heat Pump - BTC 761701317 A (02.2022)