Thomas & Betts LDAP 1200 - Manual (Page 37)

Form RZ-NA-I-LDAP, P/N 207733 (Rev 2), Page 37
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.
Size 400 has one pressure switch; Size 800 has two heat sec-
tion pressure switches and a main combustion air pressure
switch; and Size 1200 has three heat section pressure switches
and a main combustion air pressure switch. The main com-
bustion air pressure switch is located on the top of the first
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.
Main
Combustion
Air Pressure
Switch -
Models 800
and 1200 Heat Section
Pressure
Switch
36. Operating
Gas Valve(s)
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.
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.
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.
Single-Stage Valve
1/8” Outlet
Pressure Tap
1/8” Outlet
Pressure Tap
Two -Stage Valve (optional
on Model LDAP 400 only)
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.
NOTE: Operational pressure
settings and instructions for
checking pressure settings are
in Paragraph 12.
FIGURE 29 - Pressure Tap for Checking Gas Flow Shutoff
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.