Service Manual Bosch IDS 2.0 | 31
Bosch Thermotechnology Corp. | 07.2021
Data subject to change
10 Control
10.1 Crankcase Heater Control
The crankcase heater only operates when the compressor is OFF (i.e. during
standby). Refrigerant migration during the OFF cycle can result in noisy start-ups,
therefore a Crankcase Heater (CCH) is used to minimize refrigerant migration
thereby minimizing start-up noise and/or compressor damage. Its purpose is to
warm the compressor during the OFF cycle, driving refrigerant from compressor.
After extended shutdown periods (high voltage power off ) in cold weather, it
is recommended to allow CCH to be energized for at least 12 hours prior to
compressor operation by applying line voltage to heat pump with thermostat OFF.
10.2 Other Operations
The operations shown in this section are unit operations which occur only under
specifi c conditions.
10.2.1 Defrost Operation
If there is no fault code and the unit is in defrost mode, the LED display will show
“dF**” (** shows the frequency of compressor in Hz). The unit can enter defrost
mode via logic or manually.
The Demand Defrost Control (DDC) monitors the outdoor unit 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 = 18°F
— T4 ≥ 30°F, Delta T = 16°F
— T4 ≥ 19°F, Delta T = 14°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.
Defrost Termination Settings (SW5) off ers diff erent defrost termination options for
enhanced defrost for diff erent geographical and outdoor conditions.
Figure 9
ON
OFF
1 2
SW5
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 20
Manual Defrost:
1. System must have a call for heat and have been operating for a minimum of
8 minutes.
2. Press “Force” button on inverter board for 6 seconds to begin manual defrost.
3. Wait approximately 40 seconds for defrost to initiate.
4. Once defrost initiates, the display will indicate “dF”.
5. Defrost test will terminate automatically, after which the display will indicate
running speed.
6. If a second defrost test is required, repeat steps 2-5 after 5 minutes.
10.2.2 Oil Return Operation
In order to prevent the compressor from operating in a low oil condition, the oil
return operation is conducted to recover oil to the compressor. The LED display will
show “A**” during oil return operation (** shows the frequency of compressor).
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