Carrier 50TC*17 Series Service And Maintenance Instructions

36Low Pressure SwitchThe system is protected against a loss of charge and lowevaporator coil loading condition by a low pressure switchlocated on the suction line near the compressor. Theswitch is stem−mounted. Trip setting is 54 psig ± 5 psig(372 ± 34 kPa). Reset is automatic at 117 ± 5 psig (807 ±34 kPa).Supply (Indoor) Fan Motor ProtectionPERSONAL INJURY HAZARDFailure to follow this WARNING can result inpersonal injury.Disconnect all electrical power when servicing the fanmotor. Apply appropriate lockout/tagout procedures.! WARNINGMotors with 2.9 and 3.7 bhp are equipped with an internalovertemperature or protection device. The type of devicedepends on the motor size. See Table 8.The High Static option supply fan motor is equipped witha pilot−circuit Thermix combination overtemperature/overcurrent protection device. This device resetsautomatically. Do not bypass this switch to correcttrouble. Determine the cause and correct it.The Thermik device is a snap−action overtemperatureprotection device that is embedded in the motor windings.The Thermik can be identified by two blue wiresextending out of the motor control box. It is a pilot−circuitdevice that is wired into the unit’s 24V control circuit.When this switch reaches its trip setpoint, it opens the24V control circuit and causes all unit operation to cease.This device resets automatically when the motor windingscool. Do not bypass this switch to correct trouble.Determine the cause and correct it.The External Overload Breaker is an overcurrent deviceused on motors with a horsepower rating of 4.7 hp orgreater. This is a specially−calibrated circuit breaker thatis UL recognized as a motor overload controller. Whenthe current to the motor exceeds the circuit breakersetpoint, the device opens all motor power leads to themotor, shutting the motor down. Reset requires a manualreset at the overload switch. This device (designatedIFCB) is located on the side of the supply fan housing,behind the fan access panel. The Must Hold and Must Tripvalues are listed on the side of the External OverloadBreaker.Troubleshooting Supply Fan Motor OverloadTripsThe supply fan used in 50TC units is a forward−curvedcentrifugal wheel. At a constant wheel speed, this wheelhas a characteristic that causes the fan shaft load toDECREASE when the static pressure in the unit−ductsystem increases and to INCREASE when the staticpressure in the unit−duct system decreases (and fanairflow rate increases). Motor overload conditionstypically develop when the unit is operated with an accesspanel removed, with unfinished duct work, in aneconomizer−open mode, or a leak develops in the ductsystem that allows a bypass back to unit return opening.Table 8 – Overcurrent Device TypeMotor Size (bhp) Overload Device Reset1.7 Internal Linebreak Automatic2.4 Internal Linebreak Automatic2.9 Thermik Automatic3.7 Thermik Automatic4.7 External (circuit breaker) ManualCondenser Fan Motor ProtectionThe condenser fan motor is internally protected againstovertemperature.Control Circuit, 24−VThe control circuit is protected against overcurrentconditions by a circuit breaker mounted on the controltransformer TRAN. Reset is manual.PREMIERLINK CONTROLThe factory−installed PremierLink Controller includes thesupply−air temperature (SAT) sensor. The outdoor airtemperature (OAT) sensor is included in theFIOP/accessory EconoMi$er 2 package.Refer to Fig. 43 for PremierLink connection locations.NOTE: Refer to PremierLink Installation, Start−Upand Configuration Instructions. Have a copy of thismanual available at unit start−up.