Certified Drawing
IM 613 / Page 19 (Rev. 7/99)
An auto reset fault will immediately clear whenever the alarm
conditions that caused it disappear.
A manual reset fault can be cleared by cycling power to the con-
troller.
Note: The cause of a manual reset fault should be investigated
and eliminated before the unit is placed back into service.
Alarm Descriptions
Following are descriptions of the various faults listed in Table 9.
Note that some alarms are present only on certain unit ventilator
model types and configurations.
2-Pipe Units Only: All references to heating or cooling valves
(modulating or EOC) in the “Effects” sections below also apply to
2-pipe units. Whether the 2-pipe valve is a “heating” or “cooling”
valve is determined by the entering water temperature. The
changeover setpoint is 80°F (default).
Room Temperature Sensor Failure
The “Room Temperature Sensor Failure” fault will occur when
the voltage across the sensor is outside the acceptable range.
Refer to “Test Procedures” in the “Service Information” section of
this manual for information on troubleshooting sensor faults.
Effects (as applicable):
• Fan is immediately de-energized.
• Compressor is immediately de-energized.
• Reversing valve is de-energized after a delay.
• Outside air damper is closed.
• All electric heat stages are de-energized.
• Face and bypass damper is positioned to 100% face.
• Heating valve is fully opened to the coil.
• Chilled water valve is closed to the coil.
• Heating EOC valve is opened.
• Cooling EOC valve is closed.
High Pressure
The “High Pressure” fault is an indication that the high pressure
switch input (DI-4) sensed an open circuit while the controller
was calling for the compressor to run.
The high pressure switch (HP) is wired in series with the
compressor relay output (RO-2), the compressor relay coil (R1),
and the UVC alarm input. Therefore, if a high pressure condition
occurs, the compressor will be immediately shut down by the
switch; then it will be disabled by the UVC. Refer to “Test
Procedures” in the “Service Information” section of this manual
for information on troubleshooting digital input faults.
AV/AH Units Only: Because compressorized AV or AH models
are split systems, a factory-mounted high pressure switch is not
possible, and the high pressure fault is not available. On some of
these models, DI-4 is directly connected to 24 VAC to simulate a
no-fault condition.
AZ Units with Wet Heat: Note that a 3-blink fault code could be
either a high pressure or low DX coil temperature alarm.
Effects (as applicable):
• Compressor is immediately de-energized.
Low DX Coil Temperature (3-Blink Fault Code)
The 3-blink “Low DX Coil Temperature” fault is an indication that
the low temperature switch input (DI-4) sensed an open circuit
while the controller was calling for the compressor to run.
The low DX coil temperature switch (T4) is wired in series with
the compressor relay output (RO-2) and the UVC alarm input.
Switch T4 will open when the coil temperature falls below its
setpoint. Refer to “Test Procedures” in the “Service Information”
section of this manual for information on troubleshooting digital
input faults.
AZ Units with Wet Heat: Note that a 3-blink fault code could be
either a low DX coil temperature or high pressure alarm.
Effect:
• Compressor is immediately de-energized.
Low Refrigerant Temperature (Water Coil)
The “Low Refrigerant Temperature” fault will occur when the
water source heat pump is in the heating mode and the
refrigerant temperature is at or below the low limit setpoint.
Usually, a low refrigerant temperature condition is caused by in-
sufficient water flow.
Effects:
• Compressor is immediately de-energized.
• Reversing valve is immediately de-energized.
Low DX Coil Temperature (5-Blink Fault Code)
The 5-blink “Low DX Coil Temperature” fault is an indication that
the low temperature switch input (DI-5) sensed a contact closure
while the
controller was calling for compressorized cooling. (UVC’s on air
source heat pumps in the defrost cycle will ignore this alarm con-
dition.)
The low DX coil temperature switch (T4) is connected
between 24 VAC and the UVC alarm input. Switch T4 will close
when the coil temperature falls below its setpoint. Refer to “Test
Procedures” in the “Service Information” section of this manual
for information on troubleshooting digital input faults.
Effect:
• Compressor is immediately de-energized.
Low Water Coil Leaving Air Temperature
The “Low Water Coil Temperature” fault is an indication that the
low temperature switch input (DI-5) is sensing a contact closure.
The low water coil temperature fault can occur at any time,
regardless of the Control Temperature or operating mode.
The low water coil temperature switch (T6) is connected
between 24 VAC and the UVC alarm input. Switch T6 will close
when the coil temperature falls below its setpoint. Refer to “Test
Procedures” in the “Service Information” section of this manual
for information on troubleshooting digital input faults.
Note: On 2-pipe valve controlled units, the entering water
temperature determines whether the valve will be enabled for
heating. It must be greater than 80°F (default), otherwise the valve
will be closed.
Effects (as applicable):
• Outdoor air damper is closed (exhaust fan interlock
feature is overridden).
• Heating valve is positioned to 100% open to the coil
(discharge air temperature < 55°F, default).
• Heating valve is positioned 25% open to the coil
(discharge air temperature ≥ 55°F, default).
• Chilled water valve is closed to the coil.
• Compressor is immediately de-energized.
• First stage of electric heat is energized (only if fan is on).
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