Electronic Functions; Main Protection; Outdoor Fan Running Rules; Inverter Module Protection - Carrier 38MARBQ12AA1 Service Manual

ELECTRONIC FUNCTIONS

Abbreviation:
•T1: Indoor room temperature
•T2: Coil temperature of indoor heat exchanger middle.
•T2B: Coil temperature of indoor heat exchanger outlet.
•T3: Coil temperature of condenser
•T4: Outdoor ambient temperature
•T5: Compressor discharge temperature
•Td: Target temperature
•Ts: Set Point Temperature

Main Protection

Three minute delay for compressor restart
Less than a 1 minute delay for the initial start-up and a 3 minute delay
for subsequent starts.
Compressor high temperature cutout
The unit stops working when the compressor high temperature cutout
opens, and restarts after the compressor high temperature cutout
closes.
Compressor discharge temperature protection
Compressor discharge temp. T5>239°F(115°C) for 5s, compressor
stops.
Fan speed is out of control
When the indoor fan speed is too low (300RPM) or too high
(1500RPM) for a certain time, the unit stops and the LED displays the
failure.

Inverter module protection

The inverter module has a protection function for current, voltage and
temperature. If any of these protections engage, the corresponding
code displays on the indoor unit and the unit stops working.
Indoor fan delayed open function
When the unit starts up, the louver is active immediately and the
indoor fan opens 10s later. If the unit is running in the HEATING
mode, the indoor fan is also controlled by the anti-cold wind function.
Compressor preheating functions
Preheat parameters: When the T4 (outdoor ambient temperature)
<37.4°F (3°C), preheat function is activated.
Zero crossing detection error protection
If the AC detects the time interval is not correct for a continuous 240s,
the unit stops and the LED displays the failure. The correct zero
crossing signal time interval should be between 6-13ms.
Sensor protection at open circuit and breaking disconnection
If only one temperature sensor malfunctions, the air conditioner
continues to work however the error code displays on the LED, in the
event of any emergency use. If more than one temperature sensor
malfunctions, the air conditioner stops working.
Refrigerant leakage detection
This function is only active in the COOLING mode. The function
helps prevent the compressor from being damaged by a refrigerant
leakage or a compressor overload.
Open condition:
When the compressor is active, the evaporator T2 coil temperature
value has no or very little change.
24
Operation Modes and Functions
FAN Mode
1. Outdoor fan and compressor stop
2. Temperature setting function is disabled and no setting temperature
appears.
3. Indoor fan can be set to high/med/low/auto
4. The louver operates same as in the COOLING mode.
5. Auto fan
10.8°F (6.0°C)
9°F (5.0°C)
7.2°F (4.0°C)
4.5°F (2.5°C)
1.8°F (1.0°C)
COOLING Mode
Compressor Running Rules:
• When T1-Ts < -4°F (-2°C), the compressor stops.
• When T1-Ts > -1°F (-0.5°C), the compressor activates.
• When the AC runs in the mute mode, the compressor runs with
low frequency.
• When the current is more than setting value, the current protection
function activates, and the compressor stops.

Outdoor Fan Running Rules:

The outdoor unit runs at a different fan speed according to T4. For
different outdoor units, the fan speeds differ.
82.4°F (28°C)
78.8°F (26°C)
77°F (25°C)
73.4°F (23°C)
71.6°F (22°C)
69°F (20°C)
66.2°F (19°C)
62.6°F (17°C)
Specifications subject to change without notice.
T1
°F°C
a
b
c
d
e
Fig. 25 —AUTO FAN Mode
A A DC_FAN_HI_SPD_ADD
B B DC_FAN_MID_SPD_ADD
°
C C DC_FAN_MIN_SPD_ADD
D D DC_FAN_SLOW_SPD_ADD
E E DC_FAN_SSLOW_SPD_ADD
Fig. 26 —Outdoor Fan Running Rules
H
(H-L)*0.75+L
(H-L)*0.5+L
(H-L)*0.25+L
L
ADD D D D D D D D D DD
_A A A A D D D D D D D D D D D D
_ADD DD DD DD DD D D D D
PD_A A A A D D D D D D D D D D D D
SPD_A A A A A A A A D DD DD DD DD DD DD DD DD D D
SG-38MARB-01