A.O. Smith T-D2-OS Service Manual page 67

To sum it up in a chart:
Case 5 minutes have elapsed
since prior operation?
1 No
2 Yes
3 Yes
4 Yes
5 Yes
T-D2-OS installation:
After 25 minutes have elapsed since the T-D2-IN or T-D2-OS's previous firing operation, the computer
will continually check the temperatures of the inlet and output thermistors. The automatic firing
system will not activate at all unless these 25 minutes have elapsed.
When the computer checks for these temperatures, the freeze protection firing system will activate if:
< <
T 37°F and T 50°F
in out
where T is the temperature of inlet thermistor and T
in
To sum it up in a chart:
Case 25 minutes have elapsed
since prior operation?
1 No
2 Yes
3 Yes
4 Yes
5 Yes
Inlet thermistor
temperature
Any
Above 37°F
Any
37°F and below
Any
<
OR T 37°F
out
is the temperature of the output thermistor.
out
Inlet thermistor
temperature
Any
Above 37°F
Any
37°F and below
Any
67
T-D2-IN / T-D2-OS Service Manual
Output thermistor
temperature
Any
Any
Above 50°F
50°F and below
37°F and below
Output thermistor
temperature
Any
Any
Above 50°F
50°F and below
37°F and below
CONFIDENTIAL
Ver. 1.00
Will automatic
firing be activated?
NO
NO
NO
YES
YES
Will automatic
firing be activated?
NO
NO
NO
YES
YES