Daikin RDT-135c Installation And Maintenance Manual

Contents

Daikin RDT-135c Installation And Maintenance Manual Manual pdf 105 page image

IM 738-2 103Check, Test, and Start Procedures: Oil Pressure (sizes 115 to 135C only)115 to 135C only)” on page 103. If the compressor cycleson its low pressure switch, do the following:a Verify that the circuit is not short of refrigerant.b Check for low airflow.c Check for clogged filters.d Check for restricted ductwork.e Check for very low temperature return air entering theunit.f Verify that the liquid line components, expansion valve,and distributor tubes are feeding the evaporator coil.g Verify that all air handling section panels are closed.h Verify that the suction service valve (size 115 to 135only) and the liquid line service valves are completelyopen.8 Verify that the compressors stage properly. As the circuitloads up the second compressor (if available) will beenergized. Any unloaders (reciprocating compressors only)are energized when unloaded. For more information onstaging sequences, see the Binary Outputs-AuxiliaryControl Boards section of bulletin IM 696, “MicroTech IIApplied Rooftop Unit Controller.”9 Verify that the condenser fans are cycling and rotatingproperly (blowing air upward). When the compressorstarts, at least one condenser fan should also start. TheCCB1 should control the remaining condenser fans basedon outdoor air conditions. Look at keypad menu Setup/Service \ Compressor Setup \ Cond Fan1= (also look atCond Fan2=, Cond Fan3=, Cond Fan4=). Tables 4 and 5on page 20 shows recommended setpoints based on the unitsize. Cond Fan1 controls BO5, Cond Fan2 controls BO6,Cond Fan3 controls BO7, Cond Fan4 controls BO8. Referto the unit wiring diagrams and “Condenser FanArrangement” on page 4.10 Check the oil level in the compressor sightglass. If low oilis observed, it is possible that liquid refrigerant is returningto the compressor. Check the suction superheat, see“Expansion Valve Superheat Adjustment” on page 103. Itshould be between 10°F (5.5°C) and 13°F (7.2°C). See“Expansion Valve Superheat Adjustment” below.11 Close solenoid valve SV1 by turning switch PS1 to OFFThe circuit should pump down and then the compressor(s)should stop. Place the unit into the “Fan Only” modethrough the keypad menu System Summary \ System \ CtrlMode= Fan Only.12 Check refrigerant circuit #2 by repeating steps 2 through 9,substituting circuit #2 nomenclature for circuit #1nomenclature (CS2, PS2, TD2, SV2, CCB2, andcompressor #2 (and #4).Note: The unit is wired for one time pumpdown. Thecompressor will not restart on the off cycle even if thelow pressure switch closes due to small leaks in thesolenoid valve or compressor check valve.13 Verify that the condenser refrigerant subcooling at fullcapacity is between 13 and 20°F.Expansion Valve Superheat AdjustmentIt is very important that the expansion valve superheat settingbe adjusted to be between 10° F (–12° C) and 13° F (–11° C).Insufficient superheat will cause liquid floodback to thecompressor which may result in slugging. Excessive superheatwill reduce system capacity and shorten compressor life.Turn the adjustment stem clockwise to increase superheat. Notexceeding one turn, adjust the stem and then observe thesuperheat. Allow up to 30 minutes for the system to rebalanceat the final superheat setting.On refrigeration circuits with multiple expansion valves, thesuperheat adjustment should be approximately the same for allvalves in the circuit.R-407C SuperheatDue to refrigerant glide, when measuring and/or adjustingTEV superheat, it is important to use SATURATED VAPOR(Dew Point) TABLES. Example: The Pressure/Temperature(P/T) chart shows that the saturated vapor temperature, at thedew point, of R-407C for 79 psig is approximately 51°F. If theactual refrigerant temperature is 60°F, the superheat is 9°F.Checking SuperheatFollowing are recommendations for checking superheat:1 Close the unit section doors. Running the unit with itsdoors open will affect expansion valve and systemoperation considerably.2 For units with one expansion valve per circuit, check thepressure and temperature at the compressor suction valve.3 For units with multiple expansion valves per circuit, checkthe pressure at the compressor, and check the temperatureat the suction header that is fed by the valve.Oil Pressure (sizes 115 to 135C only)When the compressor has operated long enough to stabilizeconditions, proper oil pressure should be maintained. Theactual oil pressure value varies from compressor to compressorand depends upon the temperature, oil viscosity, compressorsize, and the amount of clearance in the compressor bearings.Oil pressure values from 20 psi to 60 psi (138kPa to 414 kPa)(over suction pressure) are not uncommon.The oil level in the compressor sightglass can vary widely anddepends upon the same factors listed above. In fact, it is notunusual for two compressors that serve the same circuit tohave very different oil levels. Therefore, it is recommendedthat oil pressure, not sightglass level, be used to judge whetherthere is enough oil in a refrigerant circuit. If the oil pressure islow, add additional. Refer to page 43 to find acceptablerefrigerant oils.