Freeze Protection System - A.O. Smith 710 ASME Service Manual

12-17. Freeze protection system

There are two features to the 710 models freeze protection system: the automatic fan motor system and
the ceramic heating blocks. The automatic fan motor system allows the 710 to briefly do fan motor
operation and the ceramic heating blocks will heat up whatever portion of the heat exchanger the blocks
are strapped to.
The automatic fan motor mainly focuses on providing freeze protection from the back flow of the
venting. The seven heating blocks focus on protecting the inlet and outlet piping inside the 710, as well
as the front drum pipe. The conditions to activate either feature are different from each other.
However, the two features are not mutually exclusive, because they focus on different areas of the 710.
As long as each particular feature's activation requirements are met, it is possible for both features to
operate at the same time
Ceramic heating blocks
The blocks will only activate based on what the freeze protection thermostat senses. The thermostat is
located on the fan motor. Electrical power is required for this feature to operate.
The heating blocks will activate if the thermostat senses a surrounding temperature below 36.5°F.
Once they are on, the heating blocks will only deactivate if surrounding temperatures reach above
46.4°F.
Automatic fan motor system
This feature is for only Indoor
Electrical power is required for this feature to operate.
The computer will continually check the temperatures of the inlet, outlet and mixing
thermistors.
Automatic fan motor will not work if the "Activation of the fan motor freeze protection system"
is disabled. See section12-5.
<Activate condition>
When the computer checks for these temperatures, the Automatic fan motor system will activate if:
where T is the temperature of inlet thermistor and T
in
installation.
T < 46°F AND
out
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710 / 710 ASME Service Manual
T < T - 5°F
out in
is the temperature of the output thermistor.
out
CONFIDENTIAL
Ver. 1.00