Differential Air Pressure Switch; Relay - L.B.White Boss 400 DF Manual Del Usuario E Instrucciones

FIG. 11
B. Diff erential Air Pressure Switch
The air pressure switch is a safety device that works with
the ignition control in ensuring that the motor is up to full
speed before the gas control valve opens and the igniter
sparks.
The differences between pressure in the fan section
(positive + pressure) and the burner section (negative –
pressure) close the switch contacts. Power that is sent to
the switch when there is a call for heat is returned to the
ignition control, "proving" to the ignition control that the
switch is functioning. The control then allows the ignition
trial to proceed.
Ensure the switch's tubes are fi rmly connected and not
blocked with dirt. This can also prevent proper function
of the switch.
To determine if the switch is defective, either:
• By-pass the switch
-- Do so ONLY after the motor fi rst starts. By-passing the
switch prior to motor start-up will shut down the heater.
-- If the heater starts and burns, then the switch is
defective.
OR
• Obtain a volt meter and set it to AC volts.
-- Trace the electrical wire from terminal PSO to the
switch.
-- Start the heater
-- Verify 120 VAC to the switch.
-- Do the same test at the other terminal on
the switch.
-- If there is 120 VAC to the switch, but
voltage is not coming out being fed back
to PSI on the ignition control, replace the
switch.
Boss DF Construction Heaters
When doing maintenance or service on the switch pressure
tubes, ensure the tubes are positioned as shown.
FIG. 12
POSITIVE
PRESSURE (+)
FIG. 13
C. Relay
The relay receives power from the ignition control and then
sends that power to the motor during the starting and opera-
tion phases. See the following illustration for reference of the
relay terminals when doing voltage checks at the relay. See
Fig. 14.
Terminal Function
2 120 VAC to relay from power supply
4 120 VAC from relay to motor (HEAT OR VENT)
6 Not used
8 Not used
0 120 VAC from ignition control (IND) to relay
1 Neutral
FIG. 14
Owner's Manual • Boss DF
NEGATIVE
PRESSURE (-)
19