Freeze Protection Thermostat - A.O. Smith Water Heater 520 Direct Vent Indoor Service Manual

10-21. Freeze protection thermostat

Unit Part #
Function
Failure events
Effects on the water
heater if the freeze
protection thermostat
fails
Error codes when the
freeze protection
thermostat fails
Diagnostic
Color/Number of wires
Activation and deactivation temperature of the water heater's freeze protection system
ON mode: 36.5˚F (+6.3˚F -2.7˚F)
OFF mode: above 46.4˚F
#704
AOS Part #
#719
Temperature detecting device which prevents the pipes within the water
heater from freezing. When this device detects temperatures below 36.5˚F
(2.5˚C) inside the water heater, power is supplied to the electric heaters to
prevent the water heater from freezing.
1. ON-failure (Always senses freezing temperatures, regardless of actual
temperature).
2. OFF-failure (Never senses freezing temperatures).
1. The freeze protection heaters will always be ON, causing heat damage to
components inside the water heater.
2. The freeze protection heaters will never be able to turn on, even under
freezing temperatures, causing freeze damage to the water heater.
1. Visual inspection: connection/breakage of wires and/or the body has been
broken.
2. Check resistance and voltage: proper range of values shown below.
Black - Black
ON mode: 90 to 110 VAC and less than 1 Ω
(itself)
OFF mode: less than 1 VAC and more than 1 MΩ
2.5˚C (+3.5˚C -1.0˚C)
above 8 ˚C
520 Indoor / 520 Outdoor Service Manual
319143-129 (In)
319143-144 (Out)
N/A
39
CONFIDENTIAL
Ver. 1.00
Checkpoint B1