AAON MODGAS-XWR User Manual

MODGAS-XWR2 Technical Guide
SEQUENCE OF OPERATIONS
21
Valve Failure, Force Mode & Master vs. Normal
Valve Failure
If a valve failure occurs, the board fails that stage and then continues
to the next available stage. This is to make sure that if there is a call for
heat, heat is being supplied. A valve failure consists of either a valve
no detect or a proof of ame fail. Here is what valve failures look like
for each conguration:
1V1IGN1S / 2V1IGN1S: If the modulating valve fails,
Heat 1 Relay is turned o and the board then moves to the xed
stages (if available). If the valve fails when there is rst a call for
heat, then the rst xed stage will come on immediately. Every
ignition retry period (set in the hidden congurations menu), the
board will re-attempt to detect the valve(s) and retry the ignition
process.
2V2IGN2S: If the rst stage (the rst modulating valve) fails
when there is rst a call for heat, Heat Relay 1 is turned o and
the board immediately moves to the second stage (the second
modulating valve). If the rst stage fails when the board is in
MODULATE_MODE, then normal board operation continues.
If the second stage fails, Heat Relay 2 is turned o and the board
continues normal operation and moves to the xed stages next.
Every ignition retry period (set in the hidden congurations
menu), the board will re-attempt to detect the valve(s) and retry
the ignition process.
Force Mode
This mode is used to test that the valve ring sequence is functioning.
This mode is NOT meant to replace heating mode by any means. There
is no staging in this mode, and there is no PID Loop running in this mode.
Once a stage is forced on through the Force Screen, the board will enter
Force Mode and will not leave this mode until all the stages that were
forced on have been turned o or 10 minutes pass with no user input to
the board. Here is what force mode looks like for each conguration:
1V1IGN1S: Forcing stage 1 forces Heat Relay 1 on, and
then the next screen allows the option to decide the modulation
percentage for the valve. Forcing stages 2-4 on forces Heat
Relays 2-4 on, respectively.
2V2IGN2S: Forcing stage 1 & 2 on forces Heat Relays 1 &
2 on, respectively, and the screens following each force screen
allow you to select the percent modulation for each valve. The
valves are able to modulate at dierent percentages, but keep in
mind that bringing one below the low speed cuto and another
above it will cause low speed relay diculties. Forcing stages
2-4 on forces Heat Relays 2-4 on, respectively.
2V1IGN1S: Forcing stage 1 on forces Heat Relay 1 on,
and the next screen allows the option to select the modulation
percentage (since both valves are one stage, they both
modulate at the same percentage). Forcing stages 2-4 on
forces Heat Relays 2-4 on, respectively.
2V2IGN1S: Forcing stage 1 on forces Heat 1 & 2 on, and the
screens following allow you to select the modulation percentage
for the respective valve. Even though both valves are considered
one stage, since they operate on separate relays, the option to
modulate them at dierent percentages is available. Keep in
mind that bringing one below the low speed cuto and the other
above it will cause low speed relay diculties. Forcing stages
3-4 on force on Heat Relays 3-4, respectively.
Master vs. Normal
In order to help clarify operating modes, master and normal are used to
denote two MODGAS-XWR2 boards that are communicating with one
another (i.e. one board is a Modbus master and the other is a Modbus
slave). With one MODGAS-XWR2 board, the maximum number of
modulating valves is 2, but with two boards the maximum is 4 (2 for
each board). In a master/normal operation, the secondary board is a
slave board to the master board.
To congure a master board, put the “S/A MODE” for the board
to “FORCED” and put “OPERATION” to “MASTER” (both
congurations found in the hidden screens).
To congure a slave, put “OPERATION” to “NORMAL” (found
in the hidden screens).
Here are the possible modulation congurations that can be used with
a master/slave operation:
2V2IGN2S: In this conguration, both boards utilize both
heat relays for a modulating gas valve. Stage 1 is the valve
attached to Heat 1 Relay for both boards, and stage 2 is the valve
attached to Heat 2 Relay for both boards. The valves on both
boards are always modulated to the same position, and both
boards stage up (i.e. turn on Heat 2 Relay) at the same time.
2V1IGN1S: In this conguration, both boards utilize Heat 1
Relay to turn on 2 modulating gas valves (a total of 4 for the two
boards). This means that each board has an open relay (Heat 2
Relay) for an additional on board xed stage. The two valves
on both boards (i.e. all of the 4 valves) are always at the same
modulation position. The rst stage up (i.e. stage 2) will ip
on the Heat 2 Relay on the master board, and the second stage
up (i.e. stage 3) will ip on the Heat 2 Relay on the secondary
board.

AAON MODGAS-XWR Specifications

General

Brand	AAON
Model	MODGAS-XWR
Category	Controller
Language	English