Midco DS24A - Manual (Page 7)

VIII Initial Start-up/
Adjustment Continued
For PROPANE gas, consult your supplier for method of determining firing rate.
10. Readjust the combustion air shutter to provide a quiet, soft blue flame with well defined
orange and yellow tips for NATURAL gas or with well defined yellow tips for PROPANE.
11. Check the operation of the burner; start and stop it several times with the thermostat or
operating control.
12. With the burner running, check the operation of all limit and associated controls.
13. PERFORM THE FOLLOWING FINAL ADJUSTMENTS for combustion and flue gas temperature.
Take the flue gas samples and temperature immediately ahead of the draft control.
A. The flue gas temperature should be above 325°F but not exceeding 550°F. Excessive flue
gas temperatures will result in low efficiencies. Low flue gas temperature may cause
excessive condensation. Reset gas input if necessary to adjust stack temperature.
B. Make the final setting of the combustion air shutter by checking the flue gases with an
ORSAT or similar combustion testing instrument. The carbon monoxide content should
conform to local codes, or in their absence to the level specified in the United States or
Canadian Standard referenced on the front cover of this manual; and the carbon dioxide
content should be approximately 9.5% for NATURAL and 12.1% for PROPANE, or within
the limits prescribed by local codes.
14. Check the draft control to make sure there is no spillage of flue products into the room.
15. FILL OUT THE INSTALLATION ADJUSTMENT DATA TAG and affix to the burner or gas uti-
lization equipment.
Note: For subsequent normal starting and shut-off procedure, refer to CONSUMER
INSTRUCTIONS or to the instruction plate mounted on the burner.
DANGER: Be sure that the Main Manual Shut-Off Valve, Combination Valve and
Burner Power Switch are turned off before removing any parts for service.
WARNING: Do not attempt to FIRE the burner with the burner backplate removed as
air from the blower will not reach the combustion chamber and a dangerous level of
unburned gas could accumulate.
The nozzle and electrode assembly can be removed as a unit by removing the backplate, dis-
connecting the factory installed union located between Combination Valve and Manifold Side
Plate and pulling out curved manifold pipe. Withdraw nozzle assembly, enough to permit dis-
connecting electrode leads before removing nozzle completely.
■ ■ ■ ■ Service will normally consist of inspection and cleaning, particularly the removal of any dirt
or scale in the nozzle ribbon. Check the electrodes for serious burning and the insulators for
cracks.The electrode assembly is not adjustable, if defective; replace with a new one. When
reconnecting the electrode leads refer to Figure 7 for the correct hookup. Be sure to replace
the rubber boots over the electrodes and treat the electrode leads with care. Because of high
voltage any damage to the insulation is a potential leak path.
WARNING: When reassembling burner, make sure that the manifold slide plate is
positioned in its holder and that the main gas spud is inserted into the end of nozzle,
see Figures 6 and 7.
The shelf assembly including the blower and motor, motor relay, low voltage transformer and ter-
minal board can be withdrawn as a unit after the backplate is removed and external wiring is dis-
connected.
7
Part 2 Service
IX Nozzle and Electrodes
X Blower Shelf Assembly
Figure 7: Nozzle Assembly and Electrode Assembly