C
ontrols
IM 1049-9
16 www.DaikinApplied.com
MicroTech
®
III Unit Controller
The MicroTech III Unit Controller includes built-in
features such as random start, compressor time delay,
shutdown, condensate overflow protection, defrost
cycle, brownout, and LED/fault outputs. Refer to
"Table 7:
MicroTech III Controller Status LED's" on page 18
.
The unit has been designed for operation with a
microelectronic wall thermostat selected by the manufacturer.
Do not operate the unit with any other type of wall thermostat.
Each unit has a printed circuit board control system. The low
voltage output from the low voltage terminal strip is AC voltage
to the wall thermostat. R is A/C voltage output to the wall stat.
The 24 volt low voltage terminal strip is set up so R-G
energizes the fan, R-Y1 energizes the compressor for
cooling operation, R-W1 energizes the compressor and
reversing valve for heating operation. The reversing valve
is energized in the heating mode. The circuit board has
a fan interlock circuit to energize the fan whenever the
compressor is on if the thermostat logic fails to do so.
The output to the wall stat is AC current. Terminal (R) on
the wall stat can be connected to terminal (R) on the PC
board for AC voltage.
R
= AC current
R to G
= fan only
R
to Y1 = cooling
R to W1
= heat
The MicroTech III unit controller has a lockout circuit to
stop compressor operation if any one of its safety switches
opens (high pressure switch and low pressure switch. If
compressor low suction temperature is detected, the unit
will go into the cooling mode for 60 seconds to defrost
any slush in the water-to-refrigerant heat exchanger. If
the condensate sensor detects a filled drain pan, the
compressor operation will be suspended only in the
cooling mode. The unit is reset by opening and closing
the disconnect switch on the main power supply to the
unit in the event the unit compressor operation has been
suspended due to low temperature (freezestat) switch, high
pressure switch, or low pressure switch. The unit does not
have to be reset on a condensate overflow detection.
The MicroTech III unit controller fault output sends a
signal to an LED on a wall thermostat.
Table 7 on page
18
lists the faults that cause the Alarm “A” terminal
output to indicate an alarm condition exists.
Remote Reset of Automatic Lockouts
The Remote Reset feature provides the means to
remotely reset some lockouts.
There are (3) means to reset an automatic lockout
condition:
1 .
Using the thermostat create 2 demands for capacity
within 30 seconds
2 .
Press the room sensor or thermostat timed override/
reset button for more than 10 seconds
3 .
Turn the unit power off
When the cause of the fault condition has been cleared,
and the unit transitions from not requiring any capacity
to needing any capacity twice within 30 seconds
(accomplished by user manipulation of the Heat/Cool/
Auto/Off switch on the thermostat), an alarm reset
equivalent to a tenant override button reset is generated.
The intelligent reset counter and the 24 hour timer are
cleared when this type of alarm reset is generated.
Note:
This feature only applies to thermostat controlled
systems.
For room sensor controlled units, pressing the “Override”
or “Reset” button for more than 10 seconds will apply a
ground signal to the tenant override in (screw terminal
connection at TB1 pin 4) will clear the lockout alarm once
the cause of the fault condition has been cleared.
A unit power cycle can also be used to clear an automatic
lockout if the conditions causing the fault have been
cleared.
The Intelligent Alarm Reset feature helps to minimize
nuisance trips of automatic reset lockouts caused by low
temperature faults. This feature clears faults the first two
times they occur within a 24-hour period and triggers an
automatic lockout on the 3rd fault. The retry count is reset
to zero every 24 hours.
The MicroTech III unit controller has built-in night setback
operation. A “grounded’ signal to the “U” terminal on TB3
of the unit control puts the unit into the unoccupied mode
for night setback operation. Fan operation terminates
and unit control will only respond to signal at the W2
terminal. Daytime heating and cooling operation is
locked out. +24VAC to W2 energizes the compressor
and reversing valve for heating operation. Night setback
operation can be overridden for two hours by energizing
the O on the TB2 terminal of the unit control for 4 to
10 seconds. Day thermostat setpoints then control the
heating and cooling operation. The MicroTech III unit
controller also accommodates shutdown operation
on receipt of a “grounded” signal to the “E” input,
respectively, on TB3 input terminal of the unit control.
