Carrier 48/50HC04---14 Controls, Start-up, Operation And Troubleshooting Instructions

Carrier 48/50HC04---14 Controls, Start-up, Operation And Troubleshooting Instructions Manual pdf 8 page image

8Relative Humidity Sensors (Space or DuctMounted)The accessory space humidity sensor or duct humiditysensor is used to measure the relative humidity of the airwithin the space or return air duct. The RH reading is usedto control the Humidi-Mizert option of the rooftop unit.For wiring distances up to 500 ft (152m), use a3-conductor, 18 or 20 AWG shielded cable. The shieldmust be removed from the sensor end of the cable andgrounded at the unit end. The current loop power for thesensor is provided by the RTU-OPEN controller as 24vdc.Refer to the instructions supplied with the RH sensor forelectrical requirements and terminal locations.RTU-OPEN configurations must be changed after addinga RH sensor. See below and Fig. 8 and 9 for typical RHsensor wiring.S J4--1 or J4--4 = 24vdc loop powerS J4--2 or J4--5 = 4--20mA signal inputNOTE: The factory default for dehumidification controlis a normally open humidistat.Installing Discrete InputsCompressor SafetyThe compressor safety input provides the RTU-OPENwith feedback to when the compressor is not running andshould be. This feedback is usually provided by aCompressor Lock-Out (CLO) device. Compressor safetyis a dedicated input on the configurable input 3 and tellsthe RTU-OPEN when the compressor is locked out. Thenormal condition for compressor safety is good operation.A normally open compressor safety is the factory defaultfor all units. Follow specific accessory instructions ifinstalling a CLO device. The CLO should wire into theunit’s Low Voltage terminal Board (LVTB).NOTE: Input 3 can also be wired into J--5.SW2 1 2 3 4 5 6ONIo Vin Gnd VoMOUNTINGHOLESWIRINGOPENINGa33-9141Vin - J4 -1 or J4 -4 24VdcIo - J4 -2 or J4 -5 4 -20mA outputC07201Fig. 8 -- Space Relative Humidity Sensor Typical WiringHumidistatThe accessory humidistat provides the RTU-OPEN insightto the relative humidity in the space. The humidistatreads the RH level in the space and compares it to itssetpoint to operate a dry contact. The humidistat is adedicated input on the configurable input 9 and tells theRTU-OPEN when the RH level is HIGH or LOW. Thenormal condition for humidity is LOW. A normally openhumidistat is the factory default control for theHumidi-MiZert option. To wire in the field:S J5--8 = 24 VAC source for dry contactS J5--7 = Signal inputSingle Enthalpy (Outdoor Enthalpy)The outdoor enthalpy switch/receiver (33CSENTHSW)senses temperature and humidity of the air surroundingthe device and calculates the enthalpy when used withoutan enthalpy sensor. The relay is energized when enthalpyis high (above 28 BTU/lb OR dry bulb temperature isabove 75_F) and de-energized when enthalpy is low(below 27 BTU/lb AND dry bulb temperature is below74.5_F). The enthalpy input is dedicated to input 8 andtells the RTU-OPEN when the outside air enthalpy isHIGH or LOW. The normal condition for the enthalpyinput is HIGH. Enthalpy is configured on input 8 in thefactory when it is added as an option.NOTE: The enthalpy calculation is done using anaverage altitude of 1000 ft above sea level.For field installation, refer to the enthalpy accessoryinstructions. For wiring see below and Fig. 10. TheRTU-OPEN board provides 24vac on one of the two loosegrey wires in the return air section of the rooftop near the12-pin economizer plug. To determine the correct grey,measure the voltage on the wires with power applied tothe unit. If 24-vac is sensed, then that is the grey wire thatis connected to the RTU-OPEN board at J2-7. The otheris the signal for input 8, connect it to the LOW Enthalpyterminal on the enthalpy switch/receiver. Tie into the12-pin economizer plug on pin 4 or the black wireconnected to the actuator for the enthalpy’s GNDconnection. Power can also be provided direct from theunit transformer and J5 terminal on the RTU-OPEN.S J2--7 or J5--2 = 24 VAC for enthalpy switch powerS J2--6 or J5--1 = input signalDifferential EnthalpyDifferential enthalpy control requires both an enthalpyswitch/receiver (33CSENTHSW) and an enthalpy sensor(33CSENTSEN). The enthalpy sensor must be installedin the field as the factory can only provide singleenthalpy. The enthalpy sensor must be mounted in thereturn airstream and calculates the enthalpy of the indoorair. The relay is energized when the enthalpy detected bythe return air enthalpy sensor is less than the enthalpy atthe enthalpy switch/receiver. The relay is de-energizedwhen the enthalpy detected by the return air enthalpysensor is greater than the enthalpy at the enthalpyswitch/receiver (differential enthalpy control).