520 Indoor / 520 Outdoor Service Manual
Ver. 1.00
85
CONFIDENTIAL
To sum it up in a chart:
5 minutes have elapsed
since prior operation?
Inlet
thermistor
temperature
Output
thermistor
temperature
Will automatic firing be
activated?
No
Any
Any
NO
Yes
Above 46°F
Any
NO
Yes
Any
Above 37°F
NO
Yes
Any
37°F and below
NO
Yes
46°F and above
37°F and below
YES
Ceramic heating blocks
The blocks will only activate based on what the freeze protection thermostat senses. The thermostat is
located on the intake port for 520 Indoor and left side of
computer
board for 520 Outdoor. 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
.
