York J Series - Fault Descriptions and Handling

FORM 100.50-NOM7 (808)
77
JOHNSON CONTROLS
6
FAULT DESCRIPTIONS
Failure Modes
Troubleshooting the rooftop unit is aided by the fact
that the unit stores the last 12 unit “faults” in its history
buer, and can be viewed under the History key. The
History navigation is explained in this manual under the
section on Menu Navigation and Display Descriptions.
Anytime the unit has a Fault, the System Alarm LED,
just to the right of the display will be illuminated.
Fault Descriptions
The Fault Description Table, Table 17, classies faults
into two categories, Trouble faults and Alarm faults.
Trouble faults will cause the event to be recorded into
the history buer, but will not shut the unit down.
Alarm faults will cause the event to be recorded into
the history buer, and will cause the unit to be shut
down. Both type of faults will illuminate the LED on
the OptiLogic keypad.
Clearing Faults
The nature of the shutdown determines if the unit
requires a “manual reset”, verses an “auto reset”. A
manual reset requires removal of power from the
rooftop unit control board. This can most easily be
accomplished by cycling power at the unit disconnect
switch. An auto reset will be reset automatically once
the fault has cleared itself.
Remember, when power is recycled, the control board
goes through a 5 minute self-check, with the display
showing version, address, status “no Comm”, and start-
up “Ok Ok Ok” being displayed.
MOD UNT Communication Fault
When the Expansion Input/Output controller is con-
nected via the N2 bus to the controller for a Refrig-
erant Transducer Package, Low Ambient operation,
or FlexSys option, the communication status will be
monitored. A fault is declared if the communication
is lost.
Analog Input Faults
All analog inputs will be monitored for reliability
according to the type of input connected and the range
specied. The controller monitors all AI inputs to
determine if the value at the input is within an acceptable
range. These values are listed in Table 16. The engineer-
ing units represented are also listed as applicable.
Temperature Inputs
Temperature inputs will be monitored for reliability.
If the controller determines that the input is not within
the accepted range (shorted or open), a fault will be
declared.
Voltage Inputs
Voltage inputs will be compared with the allowed volt-
age range as shown in Table 16. Inputs with voltages
outside of this range will be declared unreliable and a
fault will be declared.
Negative Pressure Safety Switch
This safety device is in series with the analog output to
the outside air damper when the unit is congured for
an Air Measuring station. A Negative Pressure safety
switch will be factory installed in the lter section of
the unit whenever a Minimum or 25/75 Air Measuring
Station is installed (none for full Air Measuring Sta-
tion), and will be located upstream of the lters. This
switch will open at negative 4 inwg for the purpose of
preventing an excessive negative pressure in the return
section, should the outside air damper fail. If the outside
air damper fails (fails closed), the MOD-DCU will drive
the return air dampers closed to increase the outside
air because it sees a decrease in airow (dampers are
closed). If the pressure exceeds – 4 inwg as a result
of the return dampers closing, the negative pressure
switch will open and remove power from the return
damper actuator. The return damper actuator is “fail
open” and will open the return dampers to relieve the
negative pressure. The MOD-DCU does not monitor
the negative pressure switch. As such this safety is
used only to prevent damage to the unit panels, and the
failure of the outside air damper will continue to exist
until noticed by service or maintenance personnel.