Communicating Furnace
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16. SUPPLY AND OUTDOOR AIR TEMPERATURE
SENSOR INPUTS (T4)
Optional field installed supply air and outdoor air sen-
sors (10K NTC thermistor) shall be read from the T4
screw terminal block.
Control to resolve temperature within +/-2°F at 70°F
There is to be an automatic detection of the supply
and outdoor air sensors. If the resistance between the
terminals is within a valid 10K thermistor range (sup-
ply air temp range = -40°F to 200°F, outdoor air temp
range = -40 to 200°F), both sensors temperatures will
be accessible.
If the resistance between the supply air terminals is
determined to be out of range to a high resistance, it
shall be interpreted as an uninstalled supplied air sen-
sor and shall not cause an error condition unless a
valid thermistor value was previously sensed on the
same power cycle. If the sensor was determined to be
present and then is opened the control should display
a fault “82”. The fault is a level 1 fault and will not in-
hibit furnace operation. Also, if the resistance between
the terminals is determined to be out of range to a low
resistance and a valid thermistor value was sensed on
the same power cycle, a fault “82” is to be displayed
on the seven segment displays.
If the resistance between the outdoor air terminals
(OAT) is determined to be out of range to a high re-
sistance, it shall be interpreted as an uninstalled sup-
plied outdoor air sensor and shall not cause an error
condition unless a valid thermistor value was previ-
ously sensed on the same power cycle. If the sensor
was determined to be present and then is opened the
control should display a fault “84”. The fault is a level
1 fault and will not inhibit furnace operation.
Also, if the resistance between the terminals on the
OAT is determined to be out of range to a low resist-
ance, a fault “84” is to be displayed on the seven seg-
ment displays only if a valid thermistor value was
previously sensed on the same power cycle.
Fault codes “82” and “84” shall only be present for
three minutes after the fault is detected. After three
minutes has expired, the fault will no longer be set
even if the condition creating the fault is still present.
These faults are also only logged into the fault buffer
one time. Should the sensor error later clear and then
appear again the same sequence as noted previously
will be repeated.
FIGURE 51
WIRING OF SUPPLY AIR (SA) AND OUTDOOR AIR (OAT) TEMPERATURE SENSORS.
97
ST-A1194-63 (BOTTOM)
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