High / Low Pressure Faults (Hp/Lp) - Daikin MicroTech III Operation & Maintenance Manual

When the E terminal is no longer grounded the unit will
automatically return to normal operation.
Note: The remote shutdown input (E) will suspend unit
operation. Disconnect power when servicing the
unit/controller.
Important Alarm Interaction Note:
Note: If a "compressor low suction temperature" or
"freeze fault" alarm is active prior to receiving the
emergency shutdown input, the fixed 60 second
defrost process will continue until its completion.
When the defrost process is complete, the unit
shall be shutdown.

High / Low Pressure Faults (HP/LP)

Normally closed high and low refrigerant pressure switches
help protect the water source heat pump from excessively
high or low refrigerant pressures. The MicroTech III unit
controller monitors these switches individually. If the
compressor is running and the HP circuit is open, the
controller enters a pressure fault mode. If the LP circuit is
open after a time delay (default of 30 seconds, adjustable if
a communication module is present) the controller enters a
low pressure fault mode. The fan operates normally during
a pressure fault condition.
Board LED Status – High/Low Pressure Faults
Pressure Yellow
HP Off
LP Off
Only brownout and remote shutdown modes have higher
priority than the pressure fault mode. See "Priority of Faults
and Modes" on page 12 and Table 4 on page 12.
When the unit is in high or low pressure fault mode the
following occurs:
1 . When JP4 is open the (A) terminal will be de-
energized, when there is a fault. A to C will be used
to indicate an alarm signal.
2 . The compressor de-energizes.
3 . The fan de-energizes.
4 . After the shutdown is complete the IV/PR(H8) output
will change state. (On to Off / Off to On).
High or Low Pressure Reset
After the HP or LP circuit is closed, the unit does not return
to normal operation until the control board is reset. The unit
is locked out in this manner until the unit can be serviced.
The control board is reset by a short interruption of unit
power, by holding down the tenant override button for
more than 10 seconds, or via the Building Automation
System (BAS).
OM 931-6 • MicroTech III Unit Controller for WSHP
Green Red
Off Flash
Off Solid
M
Low Suction Line Temperature Fault
Board LED Status – Low Suction Line Temperature Fault
Yellow
Flash
Heating Mode
When the suction line temperature falls below 28°F
on standard equipment (6.5°F on Geothermal) the low
temperature fault generates the following:
■ The reversing valve de-energizes. The compressor
and fan continue to operate in cooling mode for
60 seconds, which results in a defrost mode. This
defrosts any ice that may have accumulated in
the water-to-refrigerant coil, because of a lack of
condenser water flow in heat mode.
■ In heat mode the low temperature fault is subject to
Intelligent Reset.
■ The fault terminal "A" changes state based on JP4
jumper in defrost mode. Terminal "A" will return
to a normal "no fault" state when the temperature
recovers to 36°F for standard loop water temperature
(14.5°F for glycol protected loop temperature).
Cooling & Dehumid Mode
When the suction line temperature falls below 28°F in cool
mode the:
■ Compressor de-energizes.
■ The fan continues to run for 60 seconds.
■ Alarm output de-energizes, with JP4 = open.
■ When the suction line temperature recovers to 36°F
in cool mode the low temperature fault is subject to
Intelligent Reset. Fault automatically clears when
operating in the dehumidification mode.
Fan Only Mode
When the suction line temperature falls below the alarm
temperature based on the previous control mode.
■ Fan de-energizes.
■ Alarm output de-energizes, when JP4 = open.
■ In Fan Only mode, the low temperature fault is
subject to Intelligent Reset if the previous operating
mode was heating or cooling. If the previous
operating mode was dehumid the alarm will auto
clear.
10
t III u C
ICro eCh nIt ontroller
Green Red
Off Off
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