Raypak 503-2003 - Manual (Page 36)

36
Heater Sequence of Operation
Models 503–1503
1. The black (hot) wire lead, located at the right-mid-
dle front inside the control compartment, goes
directly to the main power switch.
2. When the main power switch is placed in the “ON”
position, the 120 VAC terminal block in the control
compartment, the N.O. contacts of pump relay, the
N.O. contacts of blower relay, the 120/24 VAC
transformer, and terminals L1 and F1 of the igni-
tion module are powered.
3. The 120/24 VAC transformer sends a 24 VAC hot
power signal to the 24V Terminal Block.
4. 24 VAC is sent from the 24V Terminal Block to the
NO pump contacts on the modulating temperature
control (pin #13), to pin TP2 of the optional alarm
relay, to terminal R of the alarm circuit on the mod-
ulating temperature control (pin #24) and the
green “Power On” LED on the front of the heater
will illuminate.
5. 24 VAC power is sent from 24V Terminal Block to
Pin P1-1 of the UDB board, the 24 VAC terminal of
the ignition control module, the common contact of
the manual high limit, pin P3-1 of the UDB board
and L1 of the Low Water Cut Off (if equipped).
6. A 24 VAC signal is sent from the NC contact of the
manual high limit to the common terminal of the
Blocked Vent Switch and to Pin P1-1 of the UDB
board. During a blocked vent condition a 24 VAC
signal is sent from the NO open contacts of the
Blocked Vent Switch to pin P3-5 of the UDB board
to indicate a safety fault.
7. During normal operation of the heater the 24 VAC
signal exits the NC contacts of the Blocked Vent
Switch and is sent to the common terminal of the
Low Gas Pressure Switch (if equipped). During a
low gas pressure condition 24 VAC is sent from
the NC contacts of the Low Gas Pressure Switch
to pin P3-6 of the UDB board to indicate a safety
fault.
8. 24 VAC is sent from the NO contacts of the Low
Gas Pressure Switch to the common terminal of
the High Gas Pressure Switch (if equipped).
During a high gas pressure condition 24 VAC is
sent from the NO contacts of the High Gas
Pressure Switch to pin P3-7 of the UDB board to
indicate a safety fault.
9. 24 VAC is sent from the NC contact of the High
Gas Pressure Switch to the common terminal of
the Low Water Cut Off (if equipped). Upon loss of
water in the heater, the Low Water Cut Off (if
equipped) will send a 24VAC signal to pin P3-4 of
the UDB board to indicate a safety fault.
10. 24VAC is sent from the NO contact of the Low
Water Cut Off to the common contact of the Auto
Reset High Limit (if equipped) and energizes the
coil of the alarm relay. If the Auto Hi Limit opens,
24 VAC is sent from the NO contacts of the Auto
Hi Limit to pin P3-3 of the UDB board to indicate a
safety fault.
11. 24 VAC is sent from the NC contacts of the Auto
Reset Hi Limit to the common terminal of the burn-
er switch located on the front exterior panel of the
heater.
12. When the burner switch is closed, 24VAC power
then travels from the NO contact of the burner
switch to the remote enable/disable connection at
terminal 11 of the rear j-box low voltage terminal
block and to the NO contact of the Enable/Disable
relay.
13. When 24VAC power is returned from terminal 12
of the rear j-box low voltage terminal block to the
coil of the Enable/Disable relay, the relay contacts
close, and 24VAC is transmitted to the Ht D (heat
demand) connection of the modulating tempera-
ture control and to the stage contact of the
modulating temperature control, pin #15.
14. When the stage contact closes on the modulating
temperature control, 24 VAC is sent to the com-
mon terminal of the flow switch and to pin
P1-3(CFH) of the UDB board. In addition, the
amber “Call-for-Heat” LED on the front of the
heater will illuminate.
15. The pump contact on the modulating temperature
control closes sending 24 VAC to the pump switch
located on the front exterior panel of the heater.
16. When the pump switch is closed, 24 VAC is sent
to the coil of the pump relay.
17. The pump relay energizes and closes the con-
tacts, starting the heater pump.
18. Upon sufficient flow, the flow switch closes and
sends 24 VAC to the common terminal of the air
pressure switch and the TH terminal of the ignition
module. If the flow switch does not close, a 24