Specifications

IM 1049-4 / Page 15 of 36
MicroTech® III Unit Controller
TheMicroTechIIIUnitControllerincludesbuilt-infeatures
such as random start, compressor time delay, shutdown,
condensateoverowprotection,defrostcycle,brownout,and
LED/faultoutputs.Table4 shows the LED and fault output
sequences.
Theunithasbeendesignedforoperationwithamicroelec-
tronic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 volt-
age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cool-
ing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onunitsizes
024 through 060). If the low temperature switch opens, the
unit will go into the cooling mode for 60 seconds to defrost
anyslushinthewater-to-refrigerantheatexchanger.After60
secondsthecompressorislockedout.Ifthecondensatesen-
sordetectsalled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 opera-
tionhasbeensuspendedduetolowtemperature(freezestat)
switch, high pressure switch, or low pressure switch on unit
sizes048thru060.Theunitdoesnothavetoberesetona
condensateoverowdetection.
The MicroTech III unit controller fault output sends a signal
to an LED on a wall thermostat. Table4 shows for which
functionsthefaultoutputis“on”(sendingasignaltothe
LED).
Table 4: MicroTech III unit controller LED & fault outputs
Mode / Fault
Status LED’s Thermostat Alarm Light
Yellow 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-engergized
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-engergized
Temp Sensor 1 Failure
Service Test Mode
On On Off De-energized
Enabled
1
Serial EEPROM
On On On De-energized
Corrupted
Network “Ofine”
Off Off Off De-enegized
Received
1
Compressor relay/compressor terminal is labeled COMP, switched line of the
same electric input as any of the L1 terminals.
Remote Reset Feature
The Remote Reset feature provides the means to remotely
resetautomaticlockoutsgeneratedbyhigh-pressureand/
orlow-temperature(inheating)faults.WhentheMicroTech
IIIunit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MicroTechIIIunitcontroller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.
TheIntelligentresetfeaturehelpstominimizenuisancetrips
ofautomaticresetlockoutscausedbyhigh-pressureand/or
low-temperature(inheating)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.
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. Day-
time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 3 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.