Thomas & Betts LDAP 1200 Limit Control 39.High Limit Control, Vent System, Troubleshooting

38.Limit Control

39.High Limit Control

40.Transformer

41.Adjustable Fan Control

If it is determined that the automatic reset limit control needs re- placing, use only a factory-authorized replacement part that is de- signed for the size of heater.

For approximate limit location, see FIGURE 22, page 34.

A manual reset high limit control is located at the top of each heat section. Do not reset high limit control without correcting the prob- lem. If it is determined that the limit control needs replacing, use only a factory-authorized replacement part that is designed for the size of heater.

See FIGURE 22, page 34, for location. Use a voltmeter to verify that there are 24 volts output from the transformer. If the trans- former is not functioning, it must be replaced. Use a replacement transformer identical to the factory-installed model.

See FIGURE 22, page 34, for location. Check the wiring connec- tions and the adjustment knob.

If it is determined that the destratification fan control needs re- placing, use only a factory-authorized replacement part that is de- signed for the heater.

42. Vent System	Check the complete vent system at least once a year. Inspection should include all
	joints, seams, and the vent terminal cap. Clean openings. Replace any defective parts.

43. Troubleshooting

Check the Lights on the DSI Integrated Control Module (Circuit Board)

The integrated circuit board monitors the operation of the heater and includes two LED signal lights that indicate normal operation and various abnormal conditions. If the heater fails to operate properly, check this signal to determine the cause and/or to eliminate certain causes. See operating sequence in Paragraph 19.

Do not attempt to repair the DSI integrated control module; the only field replaceable component is the fuse.

IMPORTANT: When using a	Control Status - GREEN LED Codes		Flame Status - YELLOW LED Codes
	Steady On	Normal Operation - No call for heat.	Steady On	Flame is sensed.
multimeter to troubleshoot the
	Fast Flash	Normal Operation - Call for heat.	Slow Flash	Weak flame (current below
24 volt circuit, place the meter’s
				1.0 microamps ±50%)
test leads into the 5 or 9 pin
	1 Flash	System Lockout (failed to detect or	Fast Flash	Undesired flame (valve
connectors located on the
		sustain flame)		open and no call for heat).
ignition control. Do not remove
	2 Flash	Main combustion air pressure
connectors or terminals from		switch or heat section pressure
the electrical components.		switch does not close with 30
Doing so can result in misinter-		seconds of venter being energized.
preted readings due to the	3 Flash	Limit or high limit switch open.
ignition control board’s fault	4 Flash	Main combustion air pressure
mode monitoring circuits.		switch or heat section pressure
		switch is closed before venter is
		energized.
	Steady Off	Blown fuse; No power; or Defective
Form RZ-NA-I-LDAP, P/N 207733 (Rev 2),		board
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