Daikin IM 986-2 VHC Installation & Maintenance Manual

Contents

IM 986-2 / Page 27 of 48Remote Reset FeatureThe Remote Reset feature provides the means toremotely reset automatic lockouts generated by high-pressure and/or low-temperature (in heating) faultsWhen the MicroTech III unit controller is in automaticlockout due to one of these faults, and the cause ofthe fault condition has been alleviated, energizingthe O-terminal for 10 seconds or more will force theMicroTech III unit controller to clear the lockout Aunit power cycle can also be used to clear an automaticlockout if the conditions causing the fault have beenalleviatedThe Intelligent reset feature helps to minimize nuisancetrips of automatic reset lockouts caused by high-pressure and/or low-temperature (in heating) faults Thisfeature clears faults the first two times they occur withina 24-hour period and triggers an automatic lockout onthe 3rd fault The retry count is reset to zero every 24hoursThe MicroTech III unit controller has built-in nightsetback operation A “grounded’ signal to the “U”terminal on TB3 of the unit control puts the unit intothe unoccupied mode for night setback operationFan operation terminates and unit control will onlyrespond to signal at the W2 terminal Daytime heatingand cooling operation is locked out +24VAC to W2energizes the compressor and reversing valve forheating operation Night setback operation can beoverridden for two hours by energizing the O on theTB2 terminal of the unit control for 3 seconds Daythermostat setpoints then control the heating andcooling operation The MicroTech III unit controlleralso accommodates shutdown operation on receipt of a“grounded” signal to the “E” input, respectively, on TB3input terminal of the unit controlMode / Fault Status LED’s Thermostat Alarm LightYellow Green Red Output-Terminal “A”Occupied, Bypass,Standby, or Tenant Off On Off EnergizedOverrideUnoccupied On On Off EnergizedCondensate Overflow On Off Off De-engergizedHigh Pressure 1 Fault Off Off Flash De-energizedLow Pressure 1 Fault Off Off On De-energizedLow Temperature 1 Fault Flash Off Off De-energizedBrownout Off Flash Off De-energizedEmergency Shutdown Off Flash Off De-energizedRoom/Return Air or Low Flash Flash On De-engergizedTemp Sensor 1 FailureService Test Mode On On Off De-energizedEnabled 1Serial EEPROM On On On De-energizedCorruptedNetwork “Offline” Off Off Off De-enegizedReceivedTable 6: MicroTech III unit controller LED & fault outputs1 Compressor relay/compressor terminal is labeled COMP, switched line of thesame electric input as any of the L1 terminals.MicroTech® III Unit ControllerThe MicroTech III Unit Controller includes built-infeatures such as random start, compressor time delay,shutdown, condensate overflow protection, defrostcycle, brownout, and LED/fault outputs Table 6 showsthe LED and fault output sequencesThe unit has been designed for operation with eithera unit mounted thermostat or a microelectronic wallthermostat, selected by the manufacturer Do not operatethe unit with any other type of wall thermostatEach unit has a printed circuit board control system Thelow voltage output from the low voltage terminal stripis AC voltage to the wall thermostat R is A/C voltageoutput to the wall statThe 24 volt low voltage terminal strip is set up so R-Genergizes the fan only R-Y1 energizes the compressorfor cooling operation, R-W1 energizes the compressorand reversing valve for heating operation The reversingvalve is energized in the heating mode The circuitboard has a fan interlock circuit to energize the fanwhenever the compressor is on if the thermostat logicfails to do soThe output to the wall stat is AC current Terminal (R)on the wall stat can be connected to terminal (R) on thePC board for AC voltageR = AC currentR to G = fan onlyR to Y1 = coolingR to W1 = heatThe MicroTech III unit controller has a lockout circuitto stop compressor operation if any one of its safetydevices is triggered (high pressure switch and lowtemperature sensor) If the low temperature sensor istriggered, the unit will go into the cooling mode for 60seconds to defrost any slush in the water-to-refrigerantheat exchanger After 60 seconds the compressor islocked out. If the condensate sensor detects a filled drainpan, the compressor operation will be suspended onlyin the cooling mode The unit is reset by opening andclosing the disconnect switch on the main power supplyto the unit in the event the unit compressor operationhas been suspended due to low temperature sensor orhigh pressure switch The unit does not have to be reseton a condensate overflow detection.The MicroTech III unit controller fault output sends asignal to an LED on a wall thermostat Table 6 showsfor which functions the fault output is “on” (sending asignal to the LED)