Carrier Thermostat Troubleshooting

Below, you can find a troubleshooting manual for some Carrier Thermostat device models. For your convenience, they are present in the form of tables: they enlist the most widespread technical issues and provide detailed instructions for fixing the problems manually or via WiFi connection. The list of error codes for issue identification is also included.

Carrier Debonair-33CS Thermostat Troubleshooting

PROBLEMSOLUTION
Display on thermostat not illuminated.Check for 24 vac at the R terminal connection. Terminal R must be connected for proper thermostat operation.
Cooling will not energize.Select COOL mode. Decrease cooling set point to 10 degrees below room temperature. Check for 24 vac at Y1 terminal. If present, thermostat is operating correctly and problem is with wiring or equipment. If 24 vac is not present, replace the thermostat. Check for Compressor Cycle per Hour Limit. Cooling may be locked out.
Heating will not energize.Select HEAT mode. Increase heating set point to 10 degrees above room temperature. Check for 24 vac at W1/ O/B terminal. If present, thermostat is operating correctly and problem is with wiring or equipment. If 24 vac is not present, replace the thermostat.
When using 4 wires (R,G,W,Y), the cooling equipment tries repeatedly to turn on, but can- not. At times the display dims or disappears.There is not enough power available. Connect a 270 ohm, 10 watt power resistor at the air conditioning equipment between terminals W and C (non-heat pump applications only).
When using 4 wires (R,G,W,Y), the heating equipment tries repeatedly to turn on, but can- not. At times the display dims or disappears.There is not enough power available. Connect a 270 ohm, 10 watt power resistor at the air-conditioning equipment between terminals Y and C (non-heat pump applications only).
When controlling a heat pump, heat comes on during cooling cycle.Configure thermostat for heat pump operation
When calling for cooling, both heating and cooling are energized.The thermostat is configured for a heat pump. Configure the thermostat for non-heat pump operation
When controlling a commercial heat pump unit, unit runs in reverse or heating is always on.Some commercial heat pumps require that Heat Pump Option on thermostat is turned OFF.

Carrier AC Thermostat Troubleshooting

SYMPTOMWHAT TO CHECK
No LCD on temperature displayCheck for 24vac between R and C at terminal connections. Both R and C must be connected for proper operation.
"E2" on temperature displayBrownout condition or too low of voltage to thermostat. Double check wiring and check for 24vac between R and C. E2 will clear 15 sec after proper voltage is restored.
"E1" on temperature displayTemperature sensor reading out of range. Check sensor for damage. If recycling power does not clear display, thermostat should be replaced.
"Clean Filter" on temperature displayAfter the selected number of hr of blower operation "clean filter" will display on LCD.
This is to remind the homeowner to "check" filter.
Press "reset filter" button to clear display and reset timer to 0.
“—“ on temperature displayIf the outdoor sensor is open, not connected, or shorted will be displayed in place of outdoor temperature.
Cooling will not come onSelect COOL mode. Set desired temperature to 10'F below room temperature. Simultaneously press FAN and INCREASE TEMPERATURE buttons to defeat timers. Check for 24vac at Y (first-stage) terminal.
If present, thermostat is OK and problem is with equipment or wiring. If not present, replace thermostat.
Heating will not come onSelect HEAT mode. Set desired temperature to 10‘F above room temperature. Simultaneously press FAN and INCREASE TEMPERATURE buttons to defeat timers. Check for 24vac at Y (first-stage) terminal (with heat pump) or W/W1 (with air conditioner) terminal.
If present, thermostat is OK and problem is with equipment or wiring. If not present, replace thermostat.

Carrier 33AWCS1 Thermostat Troubleshooting

ProblemSolution
Room Air Temperature Sensor FailureIf the sensor used to sense room air temperature, reads less than -45°C or greater than 65°C, it will be considered as failed and will display "-".
Communication FailureIf the NUI does not receive CCN communication data from the CDU for 60 seconds, the display will show"E3" error code in the Temperature display zone and '-'in the Time Display zone. Under this condition the outside temperature will be blanked. "E3" error code will be displayed and the other functionality will remain same. If this happens then check the communication cable between NUI and outdoor unit
Humidity Sensor FailureIf the sensor used to sense room Humidity reads less than 0 HR% or greater than 99 HR%, it will be considered as failed and will display "-"
EEPROM FailureIf the thermostat non-volatile memory (EEPROM) has failed, an "E4" error will be shown in the room air temperature display. When this error is present and power is cycled to the thermostat all of the installer configurations, program schedule settings and user settings will be factory default values

Carrier 33AW Thermostat Troubleshooting

Fault CodeFault
3Enter water Temperature Thermistor (EWT)
4Actual Refrigerant Temperature Thermistor BPHE
5Outdoor Air Thermistor of GMC
6Loss communication to NUI
7NUI Room Thermistor
8Unit Capacity Mismatch
9Flow Switch error / Water Pump
10EEPROM Corrupt
11OAT high than Stop Heat
12OAT low than Stop Cool
13Loss Communication to RS485 (system configuration type=6)
14Loss of Signal From CDU
15Leaving water Temperature Thermistor (LWT)
17CDU Outdoor Air Thermistor (TO)
18G-Tr short circuit protection
20Position Detection Circuit Error
21Current Sensor Error
22Outdoor Heat Exchange Sensor (TE) / (TS)
23Discharge Temperature Sensor (TD)
24Outdoor Fan Error
26Other Outdoor Error
27Compressor Lock
28Discharge Temperature Error
29Compressor Breakdown
30Low Pressure Switch
31High Pressure Release

Carrier Base Series Programmable Thermostat Troubleshooting

ProblemSolution
What if AUX HEAT appears on the display?If auxiliary heat is on. you will see AUX HEAT indicator in the display. When it is on this means the system has determined that it’s too cold outside for your heat pump to heat the house without help, so it's getting help from the electric heaters. This happens automatically.
NOTE: This indicator does not mean there is a problem with your system
What if E-IIeat appears on the display?If the heat pump is not working properly, you can manually turn on the emergency heat for extra help in healing. You’ll know there’s a problem if the house can’t seem to get warm when it’s cold outside.
You want to avoid using emergency heat, though, because it’s the most expensive option. And. of course, if you suspect a problem with your heal pump, call your heating and cooling dealer immediately.

Carrier Edge Pro Thermostat Troubleshooting

Error code Solution
CODE ElIf the display module and the equipment control module cannot communicate via two-wire connection, El will be displayed
CODE E2Not used
CODE E3If control cannot properly read outdoor temperature, and it is needed for proper operation, the display will indicate ” in the outdoor temperature location
CODE E4If internal memory fails, E4 will be displayed. Replace the thermostat
CODE E5If the thermostat cannot properly read humidity, E5 will be displayed. Replace the thermostat. If both Humidifi- cation and Dehumidification have been set to OF, the humidity value will be shown as when viewed from the humidity menu, but no E5 will be shown in the display

Carrier 997 Programmable Thermostat Troubleshooting

Problem Solution
AUXILIARY HEAT indicator is displayedThe AUX HT indicator appears on the heat pump version of the thermostat only. It is displayed when your system is operating on auxiliary heat.
NOTE: This indicator does not reflect a problem with your system
CLEAN FILTER indicator is displayedThe CLEAN FILTER indicator tells you when to clean or replace your system's air filter. Press the RESET FILTER button after cleaning or replacing the filter to turn off the indicator and restart the timer.
NOTE: This indicator does not reflect a problem with your system
HOLD indicator is displayedThe HOLD indicator reminds you that your thermostat's comfort schedule has been overridden. This function will hold the current temperature settings indefinitely, so it can be used to hold an energy-saving temperature setting for several days if needed. Press the HOLD button to resume normal system operation.
NOTE: This indicator does not reflect a problem with your system
You have a power outageAn internal power source eliminates the need to reprogram the thermostat after power outages. The comfort schedule you have entered will be maintained indefinitely. The clock will run for 72 hours
You have a system error message. The display may appear as follows: E2, or E3- indicates a problem with the indoor air sensor E2 indicates low line voltage E3 indicates a problem with the outdoor air sensor