Daikin Microtech III Operation And Maintenance Manual page 13

• Low voltage brownout protection – Brownout
condition is provided to protect the water source
heat pump motors' electrical damage due to low
voltage conditions.The MicroTech III unit controller
is designed to monitor the 24VAC power supply to
the board. If the line voltage supplied to the water
source heat pump drops, the 24VAC supply to the
control board will also drop. When the line voltage
supplied to the unit drops below approximately
80% of the unit nameplate rated value, the
controller goes into brownout condition. The
controller remains in brownout condition until line
voltage returns to approximately 90% of the unit
nameplate value. The MicroTech III unit controller
measures the input voltage and will suspend
compressor and fan operation if the voltage falls
below 80% of the unit nameplate rated value. Two
external LED status are generated and an output
is available to a "fault" LED at the thermostat.
• Condensate overflow protection (COF) (cooling
and dehumidification modes only): Senses
condensate level in condensate pan. Control will
generate a fault when condensate level is too high.
When high condensate water levels are detected
during cooling or dehumidification mode, the
controller will go into condensate overflow warning
mode. No condensate overflow warnings will occur
when the unit is running in heating modes, thus
allowing the unit to heat with high condensate
water levels. The fan operates at "Fan Only" speed
during the condensate overflow fault mode.
• Freeze fault protection – This factory-mounted
option adds a leaving water temp, LWT, sensor to
shut down compressor operation if the LWT gets
too cold. It's a dual setting sensor, set for 35°F
on boiler/tower and ground water applications
(those with no anti-freeze) in the cooling & heating
modes and extended range applications in the
cooling mode, or 13.5°F LWT on extended range
applications in the heating mode (those with anti-
freeze).
OM 1239
M
Defrost process operation:
1 . If operating in the "Heating" mode:
• The reversing valve output will be de-energized
for each compressor that requires defrosting,
placing the reversing valve in the cooling mode
and moving warm refrigerant to the coax coil.
• The compressor not requiring defrost will remain
in operation in heating mode.
• If required, Electric Heating output will remain active.
2 . If operating in the "Cooling" mode:
• Both compressors will be immediately turn off to
allow the suction line temperature to recover and
will resume operation after the min compressor off
time has been met.
If operating in the "Dehumidification" mode (if
3 .
equipped):
• The compressor requiring defrosting will be
immediately turned off.
4 . The defrost operation remains active for 60 seconds.
5 . All safety limit controls remain in place during while
in defrost.
6 . If the alarm conditions have cleared:
• Return to normal operation.
7 . If the alarm condition still remains active after the 60
second defrost:
• The compressor is immediately turned off.
• The compressor without any faults will be used.
• Electric Heat or Hydronic Heat will be used if
available, and no compressors are available.
• The fan and pump remain available for operation.
■ Heating mode
When the suction line temperature falls below 28°F on
standard equipment (6.5°F on extended range) the low
temperature fault generates the following:
•
The reversing valve on the affected circuit 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.
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t III u C
ICro eCh nIt ontroller
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