T-H2-DV/T-H2-OS Service Manual
Ver. 1.01
65
CONFIDENTIAL
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 520 models adjusts the fan motor speed to ensure that air and
fuel are always at a proper mixture ratio, minimizing emissions.
There are 3 types of FM speed adjustments, depending on the model & gas type, as shown the table
below.
<AFR normal range of values>
Type
Type A
Type B
Type C
Model
T-H2-DV
T-H2-OS
Gas type
LPG
Natural gas
LPG
Natural gas
Combustion
mode
MAX
25 to 50
31 to 48.5
20 to 46
19 to 40
MIN
3 to 10
2 to 10
3 to 18
2 to 15
・
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”. (Refer to p. 58.)
16
15
6
0
(Unit:
μ
A)
(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
+15%
FM
0%
-9%
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
+13.5%
“991” error code
Stage
+18%
FM
0%
-10.8
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
+16.2%
+20%
FM
0%
-12%
・
・
・
・
・
・
・
・
・
・
・
・
・
・
/
・
・
・
・
・
・
・
・
・
+18%
<The relationship between the AFR stage and the “10” and “99” error codes>
Type A Type B Type C
“101” error code
Default condition
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
・
