Carrier 38MGRBQ18B-3 Service Manual page 23

38MGRBQ: Service Manual
End Defrosting Action
If any one of following items is satisfied, defrosting stops and the
machine enters the normal Heating mode.
1. T3 > TempQuitDefrost_ADD °C
2. The defrosting time achieves 10 minutes
3. Turn to other modes or OFF
Outdoor Fan Control
Cooling Mode
Under normal operating conditions, the system chooses the running fan
speed according to the ambient temperature.
Fig. 32 — Cooling Mode
When low ambient cooling is in effect:
The outdoor fan speed controls logic (low ambient cooling).
When T4 < 59.(15°C) and T3 < 86.(30°C), the unit enters into the
low ambient cooling mode. The outdoor fan chooses a speed according to
T3.
When T3≥100.4.(38°C) or when T4≥68.(20°C), the outdoor fan
chooses a speed according to T4 again.
T3
°C
Exit low ambient cooling
mode
38
for 1 minute
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Fig. 33 — Cooling Mode
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
, run with high fan
30
Low
23
off
Fig. 34 — Cooling Mode
Heating Mode
Under normal operating conditions, the system chooses a running fan
speed according to the ambient temperature.
Fig. 35 — Heating Mode
Electronic Expansion Valve (EXV) Control
1. EXV is fully closed when power is turned on. The EXV will standby
with the 350P open and then opens to the target angle after the
compressor starts.
2. EXV closes with - 160P when the compressor stops. Then EXV will
standby with the 350P open and then opens to the target angle after
the compressor starts.
3. The action priority of the EXVs is A-B-C-D-E.
4. Compressor and the outdoor fan start operation only after the EXV is
initialized.
Cooling Mode
The initial open angle of EXV is dependent on indoor model size,
adjustment range is 100-400p. When the unit starts to work for three
minutes, the outdoor unit receives the indoor units' (of capacity demand)
T2B information and calculates their average.
After comparing each indoor T2B with the average. the outdoor gives the
following modification commands: if the T2B>average, the relevant
valve needs more 16p open. If the T2B = average, the relevant valve's
open range remains. If the T2B<average, the relevant valve needs more
16p close. This modification will be carried out every two minutes.
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Increase fan speed
Keep current fan speed
Decrease fan speed
Fan stop