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SUPPLY AIR INVERTER -
WITH OPTIONAL FACTORY-INSTALLED BYPASS SEQUENCE OF OPERATION
OPERATION:
1- A55 energizes K202 and K203 relay coils.
2- K203-1 N.C. contacts open to de-energize K3
relay coil. K3-1 N.O. relay contacts open to inter
rupt power to B3 blower motor through K3 N.O.
relay contacts.
3- K202 contacts close to allow power to B3 blower
motor from A96.
4- K203-2 N.O. contacts close to start A96 forward
rotation signal STF.
5- Blower B3 speed is controlled by a 0-10VDC sig
nal from A133 AO1 (or A55 PWM1/VO) to A96
terminal 2. VFD output voltage can be checked
between A96 terminals 2 and 5.
OPERATION:
1- A55 energizes the K203 relay coil.
2- K203-2 N.O. contacts close to start A96 forward
rotation signal STF.
3- Blower B3 speed is controlled by a 0-10VDC sig
nal from A133 AO1 to A96 terminal 2. VFD output
voltage can be checked between A96 terminals
2 and 5.
SUPPLY AIR INVERTER -
NO BYPASS SEQUENCE OF OPERATION
A96 FAULT SEQUENCE:
A96 will interrupt the 0-10VDC signal at terminal 2 on an in
ternal failure. A96 will retry three times before terminals B-C
open. In addition, A55 and A133 will recognize A96 B-C con
tacts are open and A55 will de-energize the K203 coil.
Optional S52 Blower Proving Switch Installed -
Refer to Blower Fault Sequence below.
BLOWER FAULT SEQUENCE:
1- The control system initiates a blower demand.
2- After 16 seconds, if S52 remains open, A55 will shut
the blower down for 5 minutes.
3- A55 will energize the blower.
4- After 16 seconds if S52 remains open, A55 will shut
the blower down for another 5 minutes.
5- After the third try, A55 will shut the unit down.
Note - The unit will remain in lockout until the failed compo
nent is fixed or A55 selection conditions are changed to:
M2-SETTINGS-CONTROL-MSAV-VFD BYPASS-ENGAGE
M3-RTU OPTION-BLOWER-VFD BYPASS DISENGAGED -
NO (configuration ID 1 set to A=automatic bypass).
6- The VFD can be set to automatically bypass the VFD
after the third start attempt. A55 selection condition
must changed to:
M2-SETTINGS-INSTALL-NEW M2-MSAV VFD BY
PASS-AUTOMATIC
M3-RTU OPTION-BLOWER-VFD BYPASS DISEN
GAGED - YES (configuration ID 1 set to M=manual
bypass)
Note - Regardless of whether the blower is started in CAV
mode using the “engage” selection or the “automatic” selec
tion, S52 will still lock out the the blower after 16 seconds.
7- Do not immediately assume the inverter has failed.
Troubleshoot the unit keeping the following in mind:
- Be sure to check multiple components and controls
when troubleshooting. A blower component, inverter,
or control failure will show the same alarms as an in
ternal VFD fault condition (open A96 terminals B-C).
- If there are no thermostat wires connected to A55 ter
minal P297, check the control system to verify a
blower demand.
- S52 is factory-installed in units equipped with the VFD
bypass option. S52 is shown on the thermostat dia
gram.
- Make sure blower demand is continuous; if blower de
mand is interrupted A96 and A55 timers will reset.
A96 FAULT SEQUENCE:
The same sequence as shown above. Note that the
same alarms will be displayed whether there is an
A96 internal fault, a blower component failure, or a
control failure.
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