Lennox LGH094U Unit Information page 89

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 A55 to A96 terminal 2. VFD output volt­
age can be checked between A96 terminals 2
and 5.
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 A55 PWM1/VO) to A96 terminal 2. VFD
output voltage can be checked between A96 ter­
minals 2 and 5.
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.
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 will recognize A96 B-C contacts are
open and A55 will de-energize the K203 coil.
Optional S52 Blower Proving Switch Installed -
Refer to Blower Fault Sequence below.
SUPPLY AIR INVERTER -
BLOWER FAULT SEQUENCE:
1-
2-
3-
4-
5-
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-
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-
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The control system initiates a blower demand.
After 16 seconds, if S52 remains open, A55 will shut
the blower down for 5 minutes.
A55 will energize the blower.
After 16 seconds if S52 remains open, A55 will shut
the blower down for another 5 minutes.
After the third try, A55 will shut the unit down.
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)
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.