Defrost Description; Compressor Crankcase Heater Description; Reversing Valve Operation - Bosch IDP Premium 18 SEER2 Series Installation Instructions Manual

13.3 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.

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) offers different defrost termination
options for enhanced defrost for different geographical and outdoor
conditions.
SW5
ON
1 2
OFF
Figure 30
Defrosting Choice SW5-1
Operating time is
ON
reduced by 10%
OFF Normal
Remarks Enter defrost
Table 18
Bosch 18 SEER2 Series Inverter Ducted Packaged Heat Pump - BTC 761703103 A (11.2022)
SW5-2 Remarks
Defrosting extended for
60 seconds
Normal Default
Quit defrost

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 forced
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.

13.4 Compressor Crankcase Heater Description

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 bearing "wash out". All CCHs must be installed
on the lower half of the compressor shell. Its purpose is to warm the compressor
during the OFF cycle, driving refrigerant from compressor. After extended
shutdown periods 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.

CCH operation energizes:
1. First time line voltage is applied and compressor discharge
temperature T5 < 53.6°F.
2. Compressor stops running for 3 hours (outdoor ambient temperature
T4 < 41°F OR compressor discharge temperature T5 < 53.6°F).

CCH operation de-energizes:
1. Compressor discharge temperature T5 ≥ 60.8°F.
2. Compressor start running.

13.5 Reversing Valve Operation


Reversing valve energizes during heat mode and de-energizes in cool
mode.
During a heat call on fi rst time operation the unit will run about 1 minute
in cooling to build up pressure for reversing valve to change.
Installation Instructions
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