Defrost Description; Compressor Crankcase Heater Description; Reversing Valve Operation - Bosch 19 SEER Series Operation Manual

Installation & Operation 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 29
Defrosting Choice SW5-1
Operating time is
ON
reduced by 10%
OFF Normal
Remarks Enter defrost
Table 15
BTC 761701105 A | 03.2019
SW5-2 Remarks
Defrosting extended
for 60 seconds
Normal Default
Quit defrost
Bosch Inverter Ducted Packaged Heat Pump | 23

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.
Data subject to change