Error 105: Heater Interlock Relay Fault - Trane ACONT900AC43UA Service Manual

Alert Code Response
Error 104: Heater relay fault
Comfort Control = Err 104
User Interface = HT ON ERR
Air Handler Fault LED = 4 Flash
Problem Description
• Voltage is being sensed by onboard sensing circuit
when no voltage should be present
- The heat relay provides a 24volt input to each bank
of electric heat when a call for auxiliary heat is present
Possible Causes/Solutions
• Disconnect harness from control board to electric
heaters and recycle power; if error clears, voltage is
being induced on harness or harness wiring by an
external source
• If error does not clear; replace control board
- Air handler fault LED will change from a 4-flash to 9-
flash if fault condition clears
- 9-flash fault will clear once harness is reconnected

Error 105: Heater interlock relay fault

Comfort Control = Err 105
User Interface = HT + LK ON ERR
Air Handler Fault LED = 4 Flash
Problem Description
• Heat relay and heat interlock relay on indoor unit
control board is stuck closed
- The heater interlock relay is an internal relay which
confirms the blower has been energized before
allowing the electric heat to energize
Possible Causes/Solutions
• Replace control board
R - A 14
Error 105: Heater interlock relay fault
Comfort Control = Err 105
User Interface = INTLK ON ERR
Air Handler Fault LED = 4 Flash
Problem Description
• Heat interlock relay on indoor unit control board is
stuck closed
- The heater interlock relay is an internal relay which
confirms the blower has been energized before
allowing the electric heat to energize
Possible Causes/Solutions
• Disconnect harness from control board to electric
heaters and recycle power; if error clears, voltage is
being induced on harness or harness wiring by an
external source
• If error does not clear; replace control board
Error 105: Heater interlock relay fault
Comfort Control = Err 105
User Interface = NTLK OFF ERR
Air Handler Fault LED = 4 Flash
Problem Description
• Heat interlock relay on indoor unit control board is
stuck open
- The heater interlock relay is an internal relay which
confirms the blower has been energized before
allowing the electric heat to energize
Possible Causes/Solutions
• Replace control board