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Marvair Scholar III™ VAISA I&S Manual 03/2019 Rev. 8
Troubleshooting Chart
Troubleshooting
The PLC is a microprocessor-based system that has the ability to provide a great
amount of information to aid in troubleshooting a malfunctioning system. In addition
to field malfunctions such as a bad Compressor Contactor, the system performs a
diagnostics on itself about 100 times per second. If any internal faults are found the
system will turn itself off and indicate a failure on the System Fault (SF) indicator. The
fault can be read by using the Microwin Programming System.
Most likely the faults will occur external to the PLC however. These faults should be
easily diagnosed by using the indicators on the front panel.
Normal Operation
The High Pressure Switch (HPS) and Low Pressure Switch (LPS) should be on all
the time. An exception will be during a low temperature start-up during which the LPS
should come on within a few moments of start-up.
The chart below shows the standard inputs and what functions should be on as a
result.
2.
Outdoor Thermostat (heat pump only).
Factory set at 40°F, this thermostat
determines the outdoor temperature at which the supplemental electric heat or wet
OAM
IBM
GW
RHS
CC
HTR
RVS
A
OFM
G
X
X
If SCKT is
on
W2
X
X
O
X
X
If HPS
is off
X
If LPS
is off
HUM
X
X
X
X
X
X
If system is
in Defrost
Mode
X
If Y is on
due to a call
for heat
X
If calling for
heat
EMS
X
X
If system is
calling for
any
function
and an
external
control is
not utilized.
If system is
calling for
any
function
and an
external
control is
not utilized.
DFC
X
X
X
X – Indicates that this function should be on.
GWR
ODS
SCKT
EHDD
LPS
X
HPS
X
Y