(3)Remove any flame simulating condition such as false light.
(4)Note that any change made in the detector or its sighting requires a pilot turndown test.
3.If using an R7290 Ultraviolet Amplifier, replace the amplifier and recheck the flame relay dropout time. If the flame relay dropout timing is still excessive, re- place the detector and check its wiring.
4.If trouble persists, replace the R4795.
H.Miscellaneous problems
1.Repeated lockouts or control failures: The most com- mon causes of repeated failures of the control or flame detector, or repeated lockouts are:
a.High ambient temperatures over 125°F (52°C). Subtract 10°F (6°C) for alarm contacts and 10°F (6°C) for 50 Hz operation.
b.Supply voltage variation greater than plus 10 to minus 15 percent.
c.Marginal flame signal.
d.Faulty flame detector.
2.Ignition interference (flame rod installations only) What it is. Ignition interference is a false signal
from a spark ignition source superimposed on the basic flame signal. It is normally associated with a marginal flame reading, and usually caused by a mar- ginal flame ground.
R4795A
TROUBLESHOOTING • SERVICE
How detected. The arc gap circuit in the rectifica- tion amplifier (Fig. 10) protects the R4795 from igni- tion interference; however, it also prevents operations when ignition interference is present above the arcing level of the device. If a shutdown is caused by ignition interference, the arc gap protector glows.
Continuous interference below the arcing level can be detected by reading the flame current with the pilot and ignition on; then with only the pilot on. Any sub- stantial difference indicates the presence of ignition interference.
Intermittent ignition interference may be due to very turbulent air in the ignition electrode area. For
How eliminated (tabulated in order of importance).
1.Provide adequate flame grounding area.
2.Be sure the ignition electrode and the flame rod are on opposite sides of the grounding area.
3.Check for the correct spacings on the ignition electrode. Spacing should be 1/16 in. (1.6 mm) to 3/32 in. (2.4 mm) for 6,000V systems; 1/8 in. (3.2 mm) to 3/16 in. (4.8 mm) for 10,000V systems.
4.Eliminate any marginal spacings at other areas along the lead routes. Replace any deteriorated leads.
Service
GENERAL
1.Only qualified personnel should attempt to service heating equipment or controls.
2.Perform all checks required in the Checkout section when replacing the R4795, or when relighting or restoring power to the system after shutdown.
3.Captive mounting screws carry current; always dis- connect power before loosening or tightening the mounting screws.
4.On each service call, check the controller for the ap- proximately correct calibration and differential; assure it is mounted securely (see Controller installation instructions).
5.Never use oil on any part of the R4795.
6.When cleaning the burner, clean the flame detector.
7.DO NOT MANUALLY PUSH IN THE R4795 RELAYS. This may damage the relays and it is an unsafe practice because it overrides the protective features of the relays. Clean relay contacts only as instructed following.
PERIODIC MAINTENANCE
The specific maintenance schedule setup will depend on several factors including type of equipment being controlled,
operating conditions (dirt and heat especially), and the cost of a nuisance shutdown. Include the following in any program:
Annually replace the vacuum tubes in the C7012 Flame Detector (if used).
Perform a flame failure check and pilot turndown test whenever the burner is serviced, and at least annually.
Inspect and clean the detector and any viewing windows as often as required by soot accumulation and heat conditions at the detector.
Do a flame current check at least monthly, and more often where a shutdown may be costly.
Clean contacts only when required by failure to operate properly.
CONTACT CLEANING
CAUTION
Open the master switch before removing cover or cleaning contacts. Line voltage is present on most contacts when power is on.
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