Specifications

IM 1059-1 / Page 15 of 36
The MicroTech III Controller is a microprocessor-based
control board conveniently located in the unit control box for
easy access through a removable access panel. The standalone
unit controller is a hard wired interface and provides all the
necessaryeldconnections.Theboardcanbewiredfor24-volt
AC output to the wall thermostat by using terminals R & C. An
LED annunciator is located on the front of the unit chassis to
allow quick check of the unit operating status.
MicroTech
®
III Operating Features
Assumes cycle fan operation-not continuous fan operation:
■ Start-up – The unit will not operate until all the inputs and
safety controls are checked for normal conditions.
■ Cooling mode – On a call for cooling from the wall ther-
mostat, the controller will energize the fan relay and stage
compressors to satisfy the space temperature setpoint. When
theloadissatised,thecontrollerwilldisablethecompres-
sor and fan.
■ Heating Mode – On a call for heating from the wall ther-
mostat, the controller will enable the fan, energize circuit
one reversing valve and circuit 1 compressor to satisfy the
space heating setpoint. If the space temperature setpoint is
notsatiseld,circuittworeversingvalveandcircuit2com-
pressor will be energized and run until the heating setpoint
atthethermostatissatised.
■ Random Start Power-up Delay Timer – In the event of a
building power outage, this feature prevents multiple units
from starting simultaneously upon building power restora-
tion.
■ Unoccupied Mode – A simple “grounded” signal between
terminals U and C (no power source required), puts the unit
into the unoccupied mode for night setback operation.
■ Interstaging Timer – A default value of 5 minutes between
staging of compressors, this feature minimizes short cycling
of compressors and improves comfort.
■ Override Mode – A switch on the deluxe automatic change-
over thermostat can be activated during the unoccupied mode
to put the unit back into the occupied mode for two hours
for after-hours heating or cooling.
■ Motorized Valve/Pump Restart – The IV/PR (H8) ter-
minals on the The MicroTech III unit controller are used
to energize (open) a motorized valve or start a water pump
to get water circulating prior to starting the compressor on
call for heating or cooling. The IV/PR (H8) terminal may
be “daisy chained” between a maximum of 200 units.
■ Brownout Protection – The MicroTech III unit controller
measures the input voltage and will suspend compres-
sor and fan operation if the voltage falls below 80% of
the unit nameplate rated value. A unique LED status is
generated.
■ Unit Shutdown – A simple grounded signal puts the unit
into the shutdown mode. Compressor and fan operations are
suspended. A unique LED status is generated.
■ Condensate Overow Protection – The MicroTech III
controller incorporates a liquid sensor at the top of the
drain
pan.Uponsensingwaterow,coolingoperationis
suspended. A unique LED status is generated.
■ Remote Reset of Automatic Lockouts – The Remote Re-
set feature provides the means to remotely reset automatic
lockouts generated by high-pressure and/or low-temperature
faults. When the MicroTech III controller is in automatic
lockout due to one of these faults, and the cause of the fault
condition has been alleviated, energizing the O-terminal
for 10 seconds or more will force the control board to clear
the lockout. A unit power cycle can also be used to clear an
automatic lockout if the conditions causing the fault have
been alleviated.
■ Intelligent Reset – The Fault Retry feature helps to mini-
mize nuisance trips of automatic lockouts caused by high-
pressure and/or low-temperature faults. This feature clears
faultstherst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.
■ Equipment Protection Control – The MicroTech III
controller receives separate input signals from the refrigerant
high-pressure switch and the low suction line temperature
sensor. In a high-pressure situation, compressor operation is
suspended. In a low temperature situation, the unit goes into
a defrost cycle where the unit is put into cooling operation
for 60 seconds until the coaxial heat exchanger is free of ice.
Each switch generates its own unique LED status.
Note: Most unit fault conditions are the result
of operating the equipment outside the unit
specications.
Mode / Fault
Status LED’
s Thermostat Alarm Light
Y
ellow Green Red Output-Terminal “A”
Occupied, Bypass,
Standby
, or Tenant Off On Off Energized
Override
Unoccupied On On Off Energized
Condensate Overow On Off Off De-energized
High Pressure 1 Fault
Off Off Flash De-energized
Low Pressure 1 Fault Off Off On De-energized
Low Temperature 1 Fault Flash Off Off De-energized
Brownout
Off Flash Off De-energized
Emergency Shutdown
Off Flash Off De-energized
Room/Return
Air or Low
Flash Flash On De-energized
Temp Sensor 1 Failure
Service Test Mode
Flash Flash Flash De-energized
Enabled
1
Serial EEPROM
On On On De-energized
Corrupted
Network “Ofine”
Off Off Off De-energized
Received
Table 13: MicroTech III Controller LED & Fault
Outputs
1
Compressor relay/compressor terminal is labeled COMP, switched line of the
same electric input as any of the L1 terminals.