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the 120 VAC pilot duty terminals, located at J-14
on the circuit board.
29. The 120 VAC signal continues to the coil of relay
K-4 (N.O.).
30. The 120 VAC signal continues to the 120 VAC
safety terminals located at J-13 on the circuit
board.
31. When the coil on relay K-4 (N.O.) is powered, the
relay contacts (K-4) close and energize the blow-
ers from the J-8 connections on the CPW board.
32. After proper air pressure is received in the air
plenum, the air pressure switches will close.
33. Power is applied to the optional equipment inter-
lock connection (normally jumpered).
34. The 24 VAC signal is then sent to the 24 VAC safe-
ty connector.
35. 24 VAC is now sent to the pressure switch (P
Switch) terminal on the ignition modules.
36. Once the pressure switch signals are received at
both ignition modules, hot surface igniter 1 is ener-
gized by a 120 VAC signal from S-1 on ignition
module 1. (The hot surface igniter must draw
greater than 3.2 amps while being energized or
ignition lockout will occur after three tries.)
37. Once ignition module 1 determines that hot sur-
face igniter 1 has heated up and operating
properly, a 24 VAC signal is output from terminal
“valve” on module 1.
38. 24 VAC signal is sent to gas valve 1.
39. The blue LED on the front of the unit is now illumi-
nated.
40. The coil of relay K-2 (N.O.) is now energized with
the (K-2) contacts closing downstream of the
stage 2 connections and upstream of the stage 3
connections.
41. The gas coming through the burners should ignite
from the heat of hot surface igniter 1 and the flame
should carry over from one burner to the other
burners of stage 1. The remote sensor is now try-
ing to sense the flame. If the flame is not sensed
within 4 seconds, the ignition module will shut
down the gas valve and retry the hot surface ignit-
er. During ignition retry the heater must perform a
15-second pre-purge and an approximately 30-
second igniter warm-up before opening gas valve
1 again. The standard ignition module will attempt
ignition a maximum of three times prior to ignition
lockout.
42. After gas valve 1 opens and flame rectification is
received, time delay relay 1 (TD-1) is powered and
starts a 5-second countdown.
43. After the 5 second countdown from TD-1, the con-
tacts close time delay relay 2 receives 24 VAC.
44. After 5 seconds gas valve 1a is now energized
allowing the remainder of stage 1 to fire.
45. After the 5-second countdown from TD-2 the inter-
nal contacts close allowing 24 VAC to sit at pin 3
of the stage 2 connection on the CPW board.
46. The temperature controller closes the stage 2 con-
tacts and gas valve 2 in energized.
47. The temperature controller closes the stage 3 con-
tacts at J-3 on the CPW board.
48. 24 VAC signal is received at gas valve 3 (Model
1259B only).
Models 1529B–2339B Only
49. Power is applied to the “TH” terminal of ignition
module 2.
50. Once the “TH” signal is received at ignition module
2, hot surface igniter 2 is energized by a 120 VAC
signal from S-1 on ignition module 2. (The hot sur-
face igniter must draw greater than 3.2 amps while
being energized or ignition lockout will occur after
three tries.)
51. Once the ignition module determines that the hot
surface igniter has heated up and operating prop-
erly, a 24 VAC signal is output from pin “valve” on
the module.
52. 24 VAC signal is received at gas valve 3.
53. The coil of relay K-5 (N.O.) is now energized with
the (K-5) contacts closing downstream of the
stage 4 connections.
54. Remote flame sensor 2 is trying to rectify flame.
55. Power is now applied to time delay relay 3 and the
contacts of TD-3 located upstream of the stage 4