THERMISTOR Operation and Testing! Inverter and Mini Split Training!

today we're going over the operation and testing of both tube thermistors and bead thermistors used on inverter systems in order to monitor the air temperature and the refrigerant temperature if you want to learn about all the electrical and the refrigerant components within a mini split make sure to check out our inverter mini split operation and surface procedures book we have the full outline available and the books available over at acservicetech.com an NTC thermistor has a wire connected on both sides of the Semiconductor in the middle and then you just have your two wires coming out now I'm measuring electrical resistance on the end of this intact bead thermistor and I just want you to see what happens when we warm the thermistor up its negative temperature coefficients that's NTC and what that means is the electrical resistance lowers as the bead thermistor warms up now B thermistor is typically used to measure the error temperature and so you have that mounted in a plastic clip and maybe even in a clear vinyl tube and that's at the inlet of the Ender coil and at the inlet of the outdoor coil a tube thermistor is used to measure the temperature of the refrigerant traveling through the indoor coil through the outdoor coil and there's also one on the compressor discharge so there's at least five thermistors on every even single zone system but on multi-zone systems you'll have a lot more now what's the difference between a tube thermistor and a b thermistor well really you have a bead thermistor that is mounted in a copper tube that's about it so you have this epoxy coated NTC thermistor basically just inside here and then you just have a little bit of rubber epoxy basically holding it in place and that's it and the tooth thermistor has an increased surface area so it takes a little bit more time for the electrical resistance to change when there's a temperature change but essentially they're the same and that's why you can use the same electrical resistance charts so for say T1 T2 T3 T4 it's all the same electrical resistance regardless of whether it's a bead thermistor or a tube thermistor but you're always going to check the manufacturers instructions in order to to verify that now there's going to be one tube thermistor that's on the compressor discharge and that's typically noted as TP and so a TP tube thermistor will have a different electrical resistance value because it's meant for a very high temperature and so that is there just a monitor to make sure that the system is not overheating basically it's not able to reject enough Heat at the indoor unit during heating mode or maybe during air conditioning mode it's the outdoor unit coil is clogged and it's just not able to reject enough heat that's what this TP thermistor is for a tube thermistor is temporarily mounted next to the refrigerant tube and it's held in place by a spring clip it's either completely covered by Spring clip or it's inside of a hollow copper tube and there's a small spring clip that's just pressing it up against the wall of the copper tubing and so the temperature of the refrigerant traveling through the tubing transfers over to the thermistor on an inverter system you're either going to have a pressure transducer or you're going to have a thermistor and typically on inverter mini split systems you're going to have a thermistor because it's much low lower in cost and on larger systems such as vrf systems you may have pressure transducers there but for inverter systems basically you're just going to have your low voltage traveling into the thermistor the thermistor is going to have a changing electrical resistance based on temperature and then you're going to have your output voltage going back to the circuit board telling the system what temperature the refrigerant is running through the lines the unit will display an error code if the thermistor is bad and so basically if it's closed completely or split open maybe it's just the wire was chafed or something like that but you can also check the calibration of this if you were to turn the power off to the mini split system so you just put it in standby mode and then pull the disconnect and then you would disconnect the thermistor connector from the PCB so we can measure electrical resistance by placing these small little probes in the back you want to make sure they're not accidentally open up the electrical connection and so we're measuring an electrical resistance of 10.84 at a temperature of 73.3 degrees now in the field I'm typically taping this sensor our temperature sensor for our tool onto the bead thermistor just to make sure that we don't have the wind affecting it or anything like that and so using this chart supplied by the manufacturer you can see that at 73 degrees we should have an electrical resistance of roughly 10.93 K ohms so you have to use the manufacturer's electrical resistance charts for checking the calibration of the thermistors so in this case you can see that this thermistor is very close and so that is good if it was off by say seven percent or ten percent the system's really going to be working inefficiently because it's not going to know the actual air temperature it's going to be kind of working under false pretenses of monitoring the air temperature so it's really easy to just diagnose these you just disconnect them with the power off and check the electrical resistance while measuring the temperature at the thermistor remember that if you want to learn more about the refrigerant and electrical components inside of a mini split system and how to to troubleshoot them how they work make sure to check out our inverter mini split operation and surface procedures book which we have available over at our website at acervicetick.com we have a full outline there so you can check out what it's all about we also have the ebook available over at Google Play and Apple Books if you want to check out some of the other mini split videos we have them linked down in the description section below hope you enjoyed yourself we'll see you next time at ac service tech Channel

Channel: AC Service Tech LLC

Views: 93,998

Keywords: acservicetech, repair, maintenance, how to, fix, hvac, hvacr, how do you, test, ac, service, tech, check, measure, read, superheat, subcooling, refrigerant, procedure, voltage, charging, temp, multimeter, freon, hvac class, hvac school, hvac training, hvac course, replace, troubleshoot, diagnose, thermistor, operation, testing, Bead Thermistor, Tube Thermistor, inverter, mini split, minisplit, temperature, air, resistance, electrical resistance

Id: V0cyVnTTMBs

Length: 5min 40sec (340 seconds)

Published: Sat Jan 14 2023