Carrier 40UV Installation, Start-up And Service Instructions Manual

Also see for 40UV: Installation and service instructions Installation, Start-Up and Service Instructions

30OUTDOOR-AIR TEMPERATURE (OAT) SENSOR — TheOAT sensor is factory-installed and factory-wired to the con-trol. The OAT sensor monitors the temperature of the outsideair entering the unit. See Fig. 13.The sensor is installed immediately upstream from theoutdoor-air damper where it will accurately sense the tempera-ture of the outdoor air entering the mixing box. The sensor con-nects to the control module T7 and T8 (OAT) as shown inTable 11.The thermistor has a range of –40 to 245 F and a resistanceof 5,000 ohms at 77 F. See Table 13 for thermistor resistanceaccording to temperature value.MIXED-AIR TEMPERATURE (MAT) SENSOR — Themixed-air temperature (MAT) sensor is factory-supplied,factory-installed, and factory-wired with each unit. The MATmeasures the temperature of air in the mixing plenum area.The MAT connects to terminals T5 and T6 on the con-trol module using 1/4-in. female quick connect terminals. SeeTable 11.The sensor uses multiple thermistor elements. This sensorprovides both mechanical and electrical averaging to achievean accurate, average temperature measurement over the entireelement length. Polarity is not a consideration. See Table 12 forresistance vs temperature values. The sensor is installed in themixing plenum before the filter so it can sense the average airtemperature. See Fig. 14.The MAT has range of –40 to 245 F with a nominal resis-tance of 10,000 ohms at 77 F.LOW-LIMIT THERMOSTAT — The low-limit thermostat(LLT) is factory-installed and factory-wired on all units withwater coils. The thermostat is used to protect the water coilsfrom freezing temperatures in the event of a malfunction bydetecting the status of a potentially damaging condition.The LLT is a 12-ft capillary tube mounted in the air stream.See Fig. 15.The LLT provides a SPDT contact. The contact provides asensor status indication to the control module and an electricalinterlock to the fan and water valves. Upon detection of a faultcondition, the unit ventilator will stop the fan, close theoutdoor-air damper, and position water valves as specified inthe sequence of operation. The LLT is factory set to trip at 38 F.The temperature setting is non-adjustable. The switch willautomatically reset and restart the fan after its temperature hasrisen by at least 5° F.Table 13 — Thermistor Resistance vs TemperatureValues for Outdoor-Air Temperature SensorThe LLT is designed to trip if any 1-ft section of the capil-lary tube senses cold air at or below the thermostat setting. Thetemperature must exceed 43 F for the thermostat to automati-cally reset to restore the circuit to normal operation.REFRIGERANT LOW-LIMIT THERMOSTAT — The re-frigerant low limit thermostat (LLR) is factory-installed andfactory-wired on all units with direct expansion coils. The ther-mostat is used to protect the water coils from freezing tempera-tures in the event of a malfunction by detecting the status of apotentially damaging condition.The LLR is a 18 in. capillary tube mounted in the air stream.See Fig. 15.The LLR provides a SPDT contact. The normally closedcontact is connected in series with the direct expansion relaycoil, such that the DX (direct expansion) control relay isdeenergized in a fault condition. The LLR is factory set to tripat 28 F. The temperature setting is non-adjustable. The switchwill automatically reset and allow direct expansion relay opera-tion when the temperature has risen by at least 5° F.RESISTANCE(Ohms)TEMPERATURE(F)168,250.0 –40121,350.0 –3188,500.0 –2265,200.0 –1348,535.0 –436,476.0 527,665.0 1421,165.0 2316,325.0 3212,695.0 419,950.0 506,245.0 685,000.0 774,028.5 863,265.0 952,663.3 1042,185.0 1131,801.5 1221,493.0 1311,244.0 1401,041.5 149876.0 158739.5 167627.5 176MIXED-AIRTEMPERATURE SENSORFig. 13 — Outdoor-Air Temperature Sensor(Part No. HH79NZ055)Fig. 14 — Mixed-Air Temperature Sensor Installedin Mixing Plenum (Part No. HH79NZ075)Fig. 15 — Low-Limit Thermostat