United CoolAir VariCool VAV Installation, Operation And Maintenance Manual
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Installation, Operation and Maintenance ManualVariCool® VAV20Subject to change without notice 1020-IM (0818)CAUTIONConfirm that any coil cleaning agents,detergents or solutions are suitable foruse on a copper tube/aluminum fin coil. Ifthe cleaning agent is to acidic or alkaline,damage to the coil fins may result.Rinse all coils thoroughly after any coil cleaningUse a suitable fin comb after the coil cleaning to straightenany bent fins.Water Side Economizer CoilIf a unit contains the optional water side economizer coil itmay also require a periodic cleaning These coils will needto be cleaned using a chemical solution These are availablecommercially Follow all manufacturer recommendationsand safety warningsWater ValvesAt least once a quarter check the water vales to make surethat no leaks are present Look at the valve stem and allpiping jointsIf any leaks are found follow the manufacturersrecommendations for tightening any seals or replacing anygasketsHard Start KitA start assist device is utilized on all single phase units Thepurpose of this device is to assist the compressor in startingunder low voltage conditionsA capacitor in conjunction with a Positive TemperatureCoefficient (PTC) relay is installed across the run andstart windings of the motor The PTC device utilizes aceramic element with a predictable thermal response tothe introduction of electric current When the compressor iscalled upon to start, the start capacitor provides a voltageboost to the start winding of the motor and causes the motorto turn As the starting current is introduced across the startwindings, the PTC element begins to warm When the PTCdevice reaches approximately 250° F (corresponding to 06- 08 seconds), the resistance in the element increases andcreates an open switch that releases the start winding fromthe circuit and the motor continues to run If the compressordoes not start before the device heats to 250° F, it will notstart until the PTC device cycles through a cool-down period(usually 2 - 3 minutes) A compressor off-cycle timer isincluded in the electrical circuit for this purposeThe time delay also helps the refrigerant system pressuresto equalize at the end of the run cycle This helps thecompressor during the starting process in that it is notattempting to start against a high discharge pressureINFORMATIONVerify that this timer is set for 3 or moreminutesChecking Hot Gas Bypass Valve1� Connect a calibrated thermocouple lead to the outletline at the hot gas bypass valve Tie wrap and insulatethe lead2� Connect a low pressure refrigerant gauge to the suctionline3� Connect a high pressure refrigerant gauge to the liquidline4� Operate the air conditioner in the cooling mode until thesystem is stabilized (Approximately 15 minutes)5� If the high side pressure is not at or above 400 psig,block off the condenser inlet air stream until thepressure is above this threshold This will simulatesystem performance level close to the design conditionof 95° F ambient6� The hot gas bypass valve setting is 104 psigA� If the suction pressure is 104 psig thethermocouple reading should be approximately117° F or higher Please note that it may benecessary to block off some of the evaporator air inorder to check this conditionB� If the suction pressure is above 104 psig thethermocouple reading should be less than 117° FC� If the suction pressure is below 104 psig the hotgas bypass valve should be adjusted to raise thepressureAdjustment Of Hot Gas Bypass ValveThe function of the hot gas bypass valve is to prevent thesuction pressure from falling below a predetermined setpoint, thereby balancing the system The set point is typically104 psig (R-410a)1� Connect a low pressure refrigerant gauge to the suctionline2� Operate the air conditioner in the cooling mode untilsystem is stabilized (Approximately 15 minutes)3� Remove the seal cap that covers the adjustment screwof the hot gas bypass valve4� Adjust the valve by turning the stem A CLOCKWISEturn will increase the pressure setting ACOUNTERCLOCKWISE turn will decrease thepressure setting One complete turn is equal toapproximately 4 psi change |
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