High / Low Pressure Faults (Hp/Lp); Low Suction Temperature Fault Heating; Low Suction Temperature Fault Cooling - Daikin MicroTech III Installation And Maintenance Manual

When the unit is in brownout condition the following
occurs:
1 . The compressor de-energizes .
2 . The IV/PR(H8) output will change state .(On to Off /
Off to On) .
3 . The fan de-energizes .
4 . Fault terminal (A) energizes (fault) .A to R will be
used to indicate an alarm signal .When the line
voltage supplied to the unit returns to acceptable
levels (90% of nameplate) the controller returns to
the current mode .

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 .
Board LED Status – High/Low Pressure Faults
Pressure Yellow
HP Off
LP Off
See Table 9 on page 16 .
When the unit is in high or low pressure fault modes the
following occurs:
1 . The compressor de-energizes .
2 . The IV/PR(H8) output will change state . (On to Off /
Off to On) .
3 . The fan de-energizes .
4 . The fault terminal (A) energizes (fault) . A to R will be
used to indicate an alarm signal .
High Pressure/Low Pressure Reset
After the HP circuit is closed, the unit does not return to
normal operation until the alarm is manually reset . The unit
is locked out in this manner until the unit can be serviced .
The alarm 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) .
Low Suction Temperature Fault
Heating
1 . When the suction line temperature falls below
28°F(standard range) or 6 .5°F(Geothermal) the
compressor output is disabled .
OM 1149-5
Green Red
Off Flash
Off Solid
M
2 . The control will attempt to recover from a low
suction temperature condition by defrosting the
water heat exchanger (coaxial coil) . See
Sequence of Operation (Heating):"
3 . When the suction line temperature increases by the
Low Temp Protect Diff (the default is 8°F) degrees .
4 . The compressor is available for heating when the
compressor minimum off timer has expired .
Defrost Sequence of Operation (Heating):
1 . Immediately turn off the compressor if operating in
the cooling or dehumidification modes.
2 . The reversing valve output is de-activated, placing
the reversing valve in the cooling mode and moving
warm refrigerant to the coax coil .
3 .
Fan speed is not changed, however "Heat Stage #1"
speed is used if the fan is presently off .
4 . If the compressor was on at the beginning of the
defrost process, then start the 60 second fixed
defrost timer .
5 . Wait for the defrost timer to expire .
6 . If the alarm condition has cleared:
• Return to normal operation .
7 . If the alarm condition remains active:
• Compressor High Capacity is turned off
• Compressor is immediately turned off, ignoring
the Compressor Minimum ON timer
• Compressor is disabled for heating and cooling
• Electric heating can be used if it is available
• Fan and pump remain available for operation
• Alarm output energizes .
• When the suction line temperature recovers to
36°F standard equipment (14 .5°F on geothermal)
the low temperature fault continues and the
compressor will be locked out .
Low Suction Temperature Fault
Cooling / Dehumidification
1 .
When the suction line temperature falls below
28°F, the compressor output is disabled . The fan
will continue to run allowing the air coil to defrost .
Once the suction line temperatures increases 8°F
(default) the compressor will be enabled once the
compressor minimum off time has expired .
Board LED Status – Low Suction Line Temperature Fault
Yellow
Flash
14
t III u C
ICro eCh nIt ontroller
"Defrost
Green Red
Off Off
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