Afr Rod Function - A.O. Smith 710 ASME Service Manual

12-4. 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 710 models 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>
Gas type
Installation
Combustion MAX
mode
MIN
・If the 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.
・Measure the values after burning the water heater for ten minutes.
・These values are read with the front cover close.
*The AFR stage can be confirmed in "Diagnostic Mode". (Section 12-1)
<The relationship between the AFR stage and the "101" and "991" error codes>
Stage
FM
+15%
16
15
+13.5%
・
・ ・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
0%
6
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
0
-9%
LPG
Outdoor Indoor
2 to 18 2 to 19
1.6 to 23 1.5 to 23
"991" error code
"101" error code
Default condition
Direct vent Outdoor
2 to 17 4.5 to 22
1.4 to 22 1.4 to 18
(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.
・15: "101" error code
・16: "991" error code
・When the "101" or "991" error code appears, see section
12-3.
52
CONFIDENTIAL
710 / 710 ASME Service Manual
Natural gas
Indoor
4 to 22
1.4 to 18
Ver. 1.00
(Unit: μA)
Direct vent
4 to 22
1.4 to 16