Carrier 38MGRBQ18B-3 - ELECTRONIC FUNCTION; Compressor Protections; Fan and Voltage Protections

38MGRBQ: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
20
ELECTRONIC FUNCTION
Abbreviation
•T1: Indoor ambient temperature
•T2: Indoor heat exchanger coil temperature
•T2B: Indoor heat exchanger exhaust coil temperature (located on
the outdoor unit)
•T3: Outdoor heat exchanger pipe temperature
•T4: Outdoor ambient temperature
•T5/TP: Compressor discharge temperature
Electric Control Working Environment
• Input voltage: 230V
• Input power frequency: 60Hz
• Indoor fan standard working amp.: <1A
• Outdoor fan standard working amp.: <1.5A
• Four-way valve standard amp.: <1A
Main Protection
Compressor Restart Delay
The compressor takes one minute to start up the first time. Further
restarts take three minutes.
Compressor Discharge Temperature Protection
When the compressor’s discharge temperature rises, the running
frequency is limited according to the following rules:
•If 221°F (105°C)  T5<230°F (110°C), maintain the current
frequency.
•If the temperature increases and T5
230°F, decrease the
frequency to a lower level every two minutes until F1.
•If T5239°F (115°C) for ten seconds, the compressor stops and
then restarts until T5<194°F (90°C).
Fan Speed Malfunction
If the outdoor fan speed is lower than 100RPM or higher than 2400RPM
for 60 seconds or more, the unit stops and the LED displays the EC 07 /
E8 failure code.
Inverter Module Protection
The inverter protection module ensures that faults related to current,
voltage, or temperature do not damage the inverter.
Low Voltage Protection
Fig. 22 — Low Voltage Protection
If these protections are triggered, the A/C unit stops and the LED displays
the failure code. The unit restarts three minutes after the protection
mechanism turns off.
NOTE: If the low voltage protection triggers and the voltage does not
restore to normal within three minutes, the protection
remains active even after the unit restarts.
Compressor Current Limit Protection
The temperature interval for the current limit is the same as the range of
the T4 frequency limit.
Fig. 23 — Cooling Mode
Table 15 — Cooling Mode
Fig. 24 — Heating Mode
Table 16 — Heating Mode
VOLTAGE
No limit
VOLT_LTM_FREQ1_ADD
VOLT_LTM_FREQ2_ADD
CoolReturnI
Difference between current limit and
shutdown current
CoolT4Zone5I
Cooling T4≥50
°C current limit value
CoolT4Zone4I
Cooling 49＞T4≥45
°C current limit value
CoolT4Zone3I
Cooling 44＞T4≥41
°C current limit value
CoolT4Zone2I
Cooling 40﹥T4≥33
°C current limit value
CoolT4Zone1I
Cooling 32＞T4
°C current limit value
CoolStopI Cooling stop protection current value
HeatReturnI
Difference between current limit and shutdown
current
HeatT4Zone4I
Heating T4≥15
°C current limit value
HeatT4Zone3I
Heating 14＞T4≥10
°C current limit value
HeatT4Zone2I
Heating 9＞T4≥6
°C current limit value
HeatT4Zone1I
Heating 5＞T4 current limit value
HeatStopI Heating stop protection current value
50
49
45
44
41
40
33
32
15
14
10
9
6
5
HeatT4Zone4I
HeatT4Zone3I
HeatT4Zone2I
HeatT4Zone1I