Thomas & Betts LDAP 1200 warranty Operating Gas Valves, Combustion Air Pressure Switches

36.Operating Gas Valve(s)

WARNING: The operating valve is the prime safety shutoff. All gas supply lines must be free of dirt or scale before connecting to the heater to ensure positive closure. See Hazard Levels, page 2.

NOTE: Operational pressure settings and instructions for checking pressure settings are in Paragraph 12.

Rotate the fan blade and re-check for adequate clearance. Repeat this procedure until the assembly is positioned properly.

5.Reconnect the fan motor wires according to the wiring diagram and close the access panel.

6.When finished with all sections, restore power to the heater and turn on the gas. Light, following the instructions on the lighting instruction plate. Check for proper operation.

Carefully remove external dirt accumulation and check the wiring connections. Size 400 has one valve; Size 800 has two valves; Size 1200 has three valves.

The combination gas valve must be checked annually to ensure that the valve is shutting off gas flow completely.

Instructions:

1)Locate the 1/8” NPT pressure tap on the combination valve.

FIGURE 29 - Pressure Tap for Checking Gas Flow Shutoff

Single-Stage Valve	Two -Stage Valve (optional
	on Model LDAP 400 only)

1/8” Outlet

Pressure Tap

1/8” Outlet

Pressure Tap

2)With the manual valve turned off to prevent flow to the gas valve, connect a ma- nometer to the 1/8” outlet pressure tap in the valve. NOTE: A manometer (fluid- filled gauge) is recommended.

3)Turn the manual valve to the ON position and the heater OFF. Use your finger to fully block the main burner orifice for several seconds. Observe the manometer with the orifice blocked, and if any pressure is indicated, the gas valve is leaking. A leaking gas valve must be replaced before the heater is placed back in operation.

37.Combustion Air Pressure Switch(es)

See FIGURE 22, page 34, for location of the heat section pressure switch. If it is determined that a pressure switch needs replacing, use only the factory-authorized replacement part that is designed for the model and size of heater being serviced.

Main	Heat Section	Size 400 has one pressure switch; Size 800 has two heat sec-
Combustion	Pressure	tion pressure switches and a main combustion air pressure
Air Pressure	Switch	switch; and Size 1200 has three heat section pressure switches
Switch -		and a main combustion air pressure switch. The main com-
Models 800		bustion air pressure switch is located on the top of the first
and 1200		heat section (see the illustration in Paragraph 34, page 36).
		NOTE: A heater operating above 6000 ft elevation requires
		high altitude heat section pressure switch(es). See Paragraph
		5.

Form RZ-NA-I-LDAP, P/N 207733 (Rev 2), Page 37