Control System - Carrier 40GXC Service Manual

Safety
3 Minute Time Delay
Freeze Protection, Indoor Coil
High Compressor Discharge Temperature
Low Voltage Protection
High Condensing Temperature
Compressor Over Current Protection
IPM Module Protection

CONTROL SYSTEM

The 53GXC(Q) units are equipped with microprocessors in the
indoor and outdoor units. They perform the following two
functions:
1. Provide safety for the system
2. Control the system and provide optimum levels of comfort
and efficiency.
3 Minute Time Delay
In order to protect the compressor, there is a 3 minute delay on
break even if the control is calling for heating or cooling.
Indoor Coil Freeze Protection
When the unit is running in the COOL or DRY MODE, the indoor
coil can freeze due to any of the following:
S Low system charge
S Reduced indoor airflow
S Restricted refrigerant flow
S Low ambient temperature (outdoor)
S Low load (indoor)
The indoor coil thermistor monitors the coil temperature
continuously. Any time the coil temperature drops below 30.2_F
(- -1_C), the compressor and the outdoor fan (30 seconds later) will
be switched off until the coil temperature rises above 42.8_F (6_C)
and the compressor was off for a minimum of 3 minutes.
Compressor
Outdoor Fan
Indoor Fan
30.2 ° F
Fig. 14 – Coil Freeze Protection
High Compressor Discharge Temperature
The compressor discharge temperature can be high due to any of
the following:
S Low refrigerant charge
S Blocked capillary
The compressor discharge line thermistor continuously monitors
the temperature and communicates with the microprocessor.
Depending on the temperature measured, the compressor will be
allowed to increase the frequency to meet the load or is forced to
run the current or reduced frequency. If the temperature gets
excessively high, the compressor will be de- -energized as shown
below:
SYSTEM SAFETIES
CODE
---
E2
E4
E5
H3
H4
H5
≥3 min
30 S
42.8° F
A09346
POSSIBLE CAUSE
Low Refrigerant Charge, Blocked Indoor Air Flow, or Dirty Air Filter
Low Refrigerant Charge, or Blocked Capillary
Low Voltage
High Ambient Temperature, or Loss of Condenser Airflow
High Ambient Temperature, or Loss of Condenser Airflow
Loss of Cooling to Heat Sink, High Ambient, Low Voltage, or Bad Connections
Stop Compressor
Reduce Comp. Freq.
No Freq. Increase
Fig. 15 – Compressor Gas Discharge Temperature Protection
When the compressor discharge temperature drops below 194 F,
the unit will resume normal operations.
Low Voltage Protection
If the incoming voltage is below the minimum allowed, E5 will be
displayed on the front panel of the indoor unit.
Condenser High Temperature Protection
Condenser high temperature can occur due to any of the following
conditions:
S High outdoor ambient
S Outdoor fan blocked
S Outdoor coil blocked
The outdoor coil thermistor continuously monitors the temperature
and communicates with the microprocessor. Depending on the
temperature measured, the compressor will be allowed to increase
the frequency if needed to meet the load or is forced to run at the
current or reduced frequency. If the temperature gets excessively
high the compressor will be de- -energized as shown below:
Stop Compressor
Reduce Comp. Freq.
No Freq. Increase
Fig. 16 – High Temperature Protection
When the outdoor coil temperature drops to 123.8 F, the unit will
resume normal operations.
NOTE: In heating the indoor fan is de- -energized 60 seconds after
the compressor is de- -energized.
12
---
208.4
217.4
230
133 136.4 143.6
° F
A09347
° F
A09348