A
DJM3
IOM-17
18 of 27 Mar 99 R3
5.
Curve Matching Procedure
Turn Service Pot to high fire (approximately 3450 RPM or 57.5 Hz) for 1 minute. Adjust the
Service Pot down very slowly until the combustion motor speed is about 3060 RPM (51 Hz).
If the pot is adjusted below 51Hz return to high fire and attempt to lower without passing
51Hz. Let the burner stabilize for 2 minutes, then re‐check O
2
reading. If O
2
has dropped to
less than the original high fire O
2
reading, adjust the Curve Matching pot. Adjusting CCW
increases the O
2
reading by reducing the voltage to the Maxitrol modulating gas valve. The
Curve Matching pot only changes the voltage to the gas valve; it does not affect fan speed.
If the curve matching pot is adjusted to the fully CCW position and the O
2
reading is still not
within 10% of the original high fire O
2
reading, add a 180‐ohm 2 watt resistor across the
modulating gas valve terminals; repeat above test until proper curve matching is achieved.
(A 150‐ohm, 2‐watt resistor may have to be used if O
2
level still does not rise to within 10%
of original high fire O
2
reading.)
Switch burner to low fire again and re‐check low fire, both at 0 VDC and 2.25 VDC. (An
addition of a resistor above may have changed the low fire setting, if it was needed.)
Lock the locking ring on the spring activated low fire adjustment screw (from step 1). Failure
to lock it may cause the screw to vibrate loose allowing low fire gas pressure to increase.
This can create sooting of burner parts and the heat exchanger. If the locking ring is missing,
drop one drop of Loctite thread locker onto the brass screw threads.
Series 50/M550, M650 AND ES350 (High Turndown Burner)
These valves have only 1 low fire adjustment (spring activated low fire).
1.
The combustion set up is similar to the above except there is no low fire bypass adjustment
on the bottom of these valves. Therefore simply set up low fire by turning the manual firing
Pot Reset Ratio to the low fire position ‐ 1250 RPM
10 RPM 20.8 Hz. (15:1 turndown set at
1195 RPM, 19.91 Hz.) Voltage to the series 50 valve should be near 0 volts DC. Adjust the
spring activated low fire adjustment at the top of the modulating gas valve (small screw)
until an O
2
reading of 16.8% to 17.5% is achieved.
2. Lock the low fire adjustment screw as described in point 7 above and then adjust the curve
matching pot as in point 5 above.
Type ES345D‐L (High Turndown Burner)
As this valve has 2 low fire adjustments the following procedure should be applied.
1.
Bring the unit to low fire using the service firing pot fully CCW. Adjust Pot Low Fire until the
combustion fan is turning 1250 RPM
10 RPM (20.8 Hz). (15:1 turndown is 1195 RPM, 19.91
Hz.) Voltage to the ES valve should be near 0 volts DC. The low fire bypass adjustment on
this valve is under the top cover on the large port and the adjustment inside it is marked:
Increase
Decrease
After removing the cover, loosen the locking screw first before making adjustment. This
should be done at 0 VDC to the modulating gas valve terminals and the
spring activated low
fire brass screw
turned fully CCW and the locking ring loosened off.
