Carrier 38MGRBQ18B-3 - Indoor; Outdoor Units Communication Protection; High Condenser Coil Temperature Protection; Outdoor Unit Anti-Freezing Protection; Low Outdoor Ambient Temperature Protection

38MGRBQ: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
21
Indoor / Outdoor Units Communication Protection
If the indoor units do not receive the feedback signal from the outdoor
units for two consecutive minutes, the unit stops and displays a failure
code.
High Condenser Coil Temperature Protection
Fig. 25 — High Condenser Coil Temperature Protection
Outdoor Unit Anti-Freezing Protection
When T2<39°F (4°C) for 250 seconds or T2< 32°F (0°C), the indoor unit
capacity demand is zero and resumes the normal operation when
T2>46.4°F (8°C) and the protection time is no less than three minutes.
Oil Return
Rules for Operation:
1. If the compressor frequency remains lower than the frequency set for
the setting time, the unit raises the frequency to the frequency set for
the setting time and then resumes the former frequency.
2. The EXV continues at 300p while the indoor units maintain their
operation. If the outdoor ambient temperature is higher than the set
frequency during the oil return, the unit stops the oil return process.
Low Outdoor Ambient Temperature Protection
When the compressor is off and T4 is lower than -31°F (-35°C) for ten
seconds, the unit stops and displays “LP.”
When the compressor is on and T4 remains lower than -40°F (-40°C)
for ten seconds, the unit stops and displays “LP.”
When T4 is no lower than -25.6°F(-32°C) for ten seconds, the unit
exits protection.
Controls and Functions
Capacity Request Calculation
Cooling Mode
Fig. 26 — Cooling Mode
Table 17 — Cooling Mode
Table 18 — Cooling Mode
NOTE: The final result is an integer.
Use Table 19 and the final capacity request to confirm the operating
frequency.
Table 19 — Cooling Mode
The maximum running frequency is adjusted according to the outdoor
ambient temperature.
Fig. 27 — Maximum Running Frequency
T3
Resume
Off
Decrease
Hold
T1 Ts
3
1
1
e
c
a
4
2
0
2
3
0
1
f
d
b
CAPACITY AREA
abcdef
NORM CODE (N)
3 2 1.5 1 0.5 0
MODEL 9K 12K 18K 24K
HP
1.0 1.2 1.5 2.5
Frequency
(Hz)
0 COOL_F1 COOL_F2
...
...
COOL_F24 COOL_F25
Amendatory
Capacity
Demand
01 2
...
...
24 25
T4FREMAXC0