24
6.4 Servicing - Fan Timer ST9103A 1028
Trouble shooting the Honeywell
electronic board ST9103
Before trouble shooting
the board,
check for the 5 amp. fuse
For accurate trouble shooting, follow step by step the Trouble Shooting Chart.
Step
Possible Cause
Check-out procedure
Corrective action
No Heat
1
Incoming supply
Check for 120 Volts
between terminal S2 and 3
on electronic fan control
Yes - Move to next step
No - Check breaker main power switch
2
Transformer
Check for 120 Volts between
terminal S3 and 4 on
electronic fan control.
Check for 24 Volts between
terminal X and C on
electronic fan control
Yes - Move to next step
No - Check for bad connection
Yes - Move to next step
No - Change Transformer
3
Electronic Fan
control
Check for 24 Volts between
R and C
Yes - Move to next step
No - Change the electronic board
Check for 24 Volts between
terminal W and C
Yes - Move to next step
No - Check thermostat and wiring
4
Warning: Make sure the quick connect cable is fully inserted on the board
Limit Control
Check for 120 Volts on each
terminal of the high limit
Yes - Move to step # 5
No - Move to next step
Check for 120 Volts coming
from the main plug-in of the
electronic fan control to the
limit control
Yes - Move to next step
No - Change the electronic fan control
Check for 120 Volts coming
out of the limit control
Yes - Move to step # 5
No - Failure on the limit control circuit
. Temperature too high
. Bad limit control
