Afr Rod Function - A.O. Smith 110 Indoor Service Manual

12-5. AFR rod function

<Function>
The AFR rod checks flame conditions during combustion. When the AFR rod detects unexpected flame
conditions, the computer board of the 110 adjusts the fan motor speed to ensure that air and fuel are
always at a proper mixture ratio, minimizing emissions.
<AFR normal range of values>
Model
Gas type
MAX
Combustion
mode
MIN
If the detected AFR value is higher than the normal value, the FM speed is increased.
If the AFR value is lower than the normal value, the FM speed is decreased.
These values are read with the front cover close.
Measure the values after burning the water heater for ten minutes.
*The AFR stage can be confirmed in "Diagnostic Mode". (Section 12-1)
<The relationship between the AFR stage and the "10" and "99" error codes>
Stage
FM
+15%
16
+13.5%
15
14
+12%
6
0%
-9%
0
T-KJr2-IN
LPG
7.0 to 24.0
2.0 to 8.0
"99" error code
"10" error code
"10" error code
Default condition
110 Indoor / 110 Outdoor Service Manual
Natural gas
7.5 to 18.0
2.0 to 7.0
(Condition of AFR stage)
0 to 5: Air-rich
In order to solve the "air excess" problem, the fan motor
speed is automatically decreased and AFR combustion
stage goes down.
6: Default
7 to 16: Gas-rich or Air shortage
In order to solve the "air deficiency" problem, the fan
motor speed is automatically increased and AFR
combustion stage goes up.
14 and 15: "10" error code
16: "99" error code
When the "10" or "99" error code appears, see section
12-4.
49
CONFIDENTIAL
T-KJr2-OS
LPG Natural gas
5.6 to 26.0 8.0 to 24.0
1.5 to 15.0 1.5 to 8.4
Ver. 1.01
(Unit: μA)