Refrigerator Compressor Not Running? Test The Start Relay, Overload, Capacitor, PTC Thermistor

hey guys this is Craig McKee out here with AC service tech and today what we're going over is troubleshooting a refrigerator compressor that doesn't start I want you to first be aware of that there could be multiple different components on the inside to here when you remove this cover so make sure that you have the power off to the compressor and then on the inside I'm gonna show you the different examples of what could be found in here and also how to troubleshoot them check out our ebook and also our paperback the refrigerator charging and service procedures for air conditioning in this book we go over the system preparation for refrigerant check in the refrigerant charge and also troubleshooting you see that in this ebook you can even zoom right in in order to read the saturated temperatures on your gauge sets so this is available over at AC service tech comm and we have the paperback available at so in this case right here this is a pill type PTC thermistor and right here you see that the pill is on the inside so typically you're gonna have a closed cover like that but I just wanted to show you what this one looks like here is an external compressor protector and that is in case the compressor has a hard time starting so over here you see a current starting relay and this one is in the downwards position and another external compressor protector so they're both mounted here and on this one right here you have a this is a start capacitor and what you have is a time starting device right here on the inside of a time starting device which is an electronic control you'll also have the external compressor protector integrated on the inside right here you have a different type of compressor protector right here and this one is a current starting relay that's in a different orientation than the other one we were looking at previously as well you can also have a start capacitor integrated on to your compressor in order to help it turn on so there's a bunch of different set ups and I want to show you over on this compressor right here that when you remove the PTC thermistor some compressors have the compressor terminals where we have one on the top and two on the bottom and over on this one right here you see that you have one on the bottom and two at the top so I would recommend that you take a photo of the components first before you remove them and some of these components come in different orientations such as the PTC thermistors right here this right here is supposed to go on to the run terminal so in this case you can see that this one would go on to a compressor where this is going on to the run terminal and on the inside it's going to go to the the start terminal so each compressor is even built differently as well as having different components so I have individual videos on troubleshooting each of these components in the description section below but I'm going to give you a quick run-through and quick troubleshooting for each of these style components here we have the two types of external compressor protectors and regardless of which one you test for resistance values still going to get some resistance so we have our multimeter set on ohms and we're going to check our resistance value and you want to make sure that you don't get oh well and you don't get zero point zero ohms of resistance you're going to have something higher than zero point zero so in this case you see we were reading 0.2 0.3 ohms and basically what's going to happen is you're gonna have your a common wire attached rate to here and then this is going to be on your common terminal of your compressor so it's going through this safety device and if you were drawing high amperage and the compressor was not starting then this would open up the electrical circuit and it would read oh well if you were reading this while this component was hot and it had just tripped but it should reset on the inside you see that there's a thermo disc on the inside and when you're drawing a high amperage you see that this little electric resistance coil is going to be heating up this thermo disc in order for it to pop and when it pops it's going to be opening up the electrical connection right over here so that's how this component works and right over here you see that there's a wire on the inside of this and also on the inside of this on top of that wire you see that you have your thermo disc once again and this one will pop and it has the contacts on the side and it works into the same premise and the only thing is this is on the outside of the compressor not on the actual terminal itself but it's pressed up against the side of the compressor at the top of the compressor and it uses the heat from the compressor as well as the the heating up of this electric resistance coil in order to to pop this thermo disc right here so when you're checking the resistance value of these you're going to not get zero point zero ohms of resistance but you're going to have something fairly close like point one usually on these now you see that this one has nothing on it because there is no thermo disc inside when you test this component right here that is a should be a good component we're going to get some type of a resistance value and you see we're reading point one ohms of resistance so same thing with this one you see that the thermodisc is inside and some of these have a blank off on the on the face of these so you may not even see the thermo disc inside but we got to wait till these cool down and then test the resistance value so here you see 0.1 ohms of resistance so if it's oh well it's not going to allow the compressor to start and you gotta wait till these get cool in order to test them make sure that when you're replacing these components you're replacing them with the exact same specs so on these you'll see the model number stamped on the side so with any type of component that you're replacing you replace it with the exact model number here are the PTC thermistors and if you have one taken off and you can shake it and you hear rattling around on the inside and that PTC thermistor is bad that means that it's completely broken on the inside it should look like this on the inside and not like this on the inside so you can see that that one was bad and when it is bad you may read a very low resistance value because you may have a chunk across there or the contacts themselves are actually touching and you see in this case that you're reading no resistance value whatsoever in this case you see that you have a good PTC thermistor on the inside and I want to show you what you should be reading right here resistance value wise you're reading 4.9 and that one is good let's read this one this one should be good as well 4.7 ohms of resistance and if these are hot if these were just allowing the compressor to turn on and now they're in the cooling down mode they're going to be a higher resistance value so this is after the PTC thermistor is cooled down that we're checking these resistance values so this one has 7.5 so how this works is you have this tap connected to the run terminal of the compressor and the power comes in and it puts power onto the start tap of the compressor through the PTC thermistor but as the compressor is drawing amperage through this thermistor it's the thermistor is heating up and it's going to end up opening up the electrical circuit between the run and start so that's going to allow the compressor to start by having power up both the run and the start for the initial startup period and then it's going to open up the electrical circuit that's how it's supposed to operate but if this is broken on the inside it may not supply any voltage to the start cap or it can accidentally hurt the compressor by applying voltage to the start the entire time and that would end up possibly burning out the compressor but that's why we have the external compressor protectors as well to help open up the electrical circuit in the case of a problem these are the time starting devices and all needs to see that you have the external compressor protector integrated onto the inside and you see it on this one as well and on the back you have a capacitor so on this one it's on the side so there's the start capacitor start capacitor start capacitor and on this one it's right back here so these can just be removed and tested so you just take it and you just pull it and then you can test the actual capacitor itself so this one right here says 15 UF so we can take our multimeter right here and change this to MFD so MFD is the same thing as UF and it's reading micro farad's and then you can take a ten thousand ohm resistor crossed here or you can take a screwdriver and what you're trying to do is you're trying to get the residual voltage off of that start capacitor then you can take your multimeter and you can test your micro farad level and you want to give your multimeter about ten seconds five ten seconds in order to get a good reading and the capacitance reading should be within about five percent of what the reading is on the capacitor so you see we're reading fourteen point eight four and this one right here is fifteen UF as well so you want to give the multimeter time and that one's reading fifteen point four one so those are both very close to their specs in fact this one's a little bit higher but for a start capacitor that's only helping the compressor start for just a very brief moment in time so just for the first quarter or a second or so that's not going to make that big of a difference so this door capacitors can be tested individually and then you can test the compressor protector such as this right here you can just check the resistance value so we do for that is let's just go back to resistance which is the Omega or the upside-down horseshoe right there and you're gonna put one probe right there into the compressor protector and one in the top so you see that we're reading point two ohms of resistance point 1 ohm or resistance so we went over those earlier so that compressor protector is good so if you were to test the compressor by itself and check the the winding taps against the ground and and check them as well I have a video on that link in the description section below and you check the compressor protector and you check the start capacitor and you know that you have good voltage going in then you know that this component is bad so there's not a great way to test these since there's the control board on the inside so you're going to test everything else around that in order to determine if this is the faulty component here you have occurrence starting relay and this one is facing a downwards position right here and this one here is faced in the upwards position and it also has a integrated compressor protector on the bottom so we know how that works from earlier and this one here is a current starting relay with a start capacitor attached and so this one's facing the downwards position and what happens is you have your voltage coming into the current starting relay and then that voltage also goes over to the start capacitor over here and then it comes out of the start capacitor over to the lead on the current starting relay and what's going to happen as this is going to allow the voltage from the start capacitor it's going to allow it into the start tap right here for the compressor so that's only going to happen after the compressor has a high amperage and then after that the iron core in here is going to suck up and it's going to allow the voltage from the start capacitor into the start tap of the compressor in order for it to turn on and what's going to happen then is once it turns on it's then going to drop this iron core and it's going to basically open up the electrical circuit and it's not going to allow any more voltage to that start winding so this right here is how that works for the start capacitor with the current starting really attached the other ones are just allowing the voltage coming in so the voltage right here goes into the the run and so you can see that it wraps around the iron core and it comes in right here and goes into the compressor on the run and after it starts the sending the voltage in the the high current pulls up the iron core and allows the run and the start to connect so you're going to get the voltage over at the start winding now and then the voltage is going to help the compressor start once the compressor starts and the amperage lowers the iron core on the inside falls down and then you're going to have the start tap out of the electrical circuit and the compressors can continue to run by supplying voltage into the run and then you're also going to have where it's connected to the common terminal through the compressor protector so I have a video on these as well so you can check that out for more details but I'm just going to show you quickly how to troubleshoot these and if this one is normally in the downwards position then that means that the iron core on the inside is down the ELMO and so you should not get any resistance value whatsoever when you're testing it in this angle so once you flip it up if there's if there's no pitting on the contacts and there's no carbon dust and you should be reading 0.0 ohms of resistance here you see that we're reading right about 4 ohms of resistance so you see that this one is older and it has some dust in there and stuff like that also the the iron core is going to have some force when it comes upwards so that's going to help it as well to make that contact so right here if you had zero point zero that would be bad and right here you want to have as close to zero point zero as possible when you flip this in this direction now also what you could do is you can test from here to here to see if that coil is bad so right there you see that we have 0.1 or zero you should have a extremely low resistance I so it should be very close to zero ohms because this wire is is very thick so so that is all good right there with this current starting relay right here we would test right between these two pins because those are going to the the two contacts the run and start and you should not read any resistance reading here so it should read oh well when this one is upright and then when this is downwards you should have a good resistance reading here so right now we're reading 3.8 see if we can get the iron core to sit down there a little bit better so we're still reading there we go point 2 ohms of resistance so you want to make sure that your probes are on those contacts good and this one is still good so that's how you test that in reference to start capacitors if you see there's any liquid or oil coming out of the capacitor then you know that that's bad in reference to testing in order to try to get a accurate MFD reading then you would have to cut the resistor off this is a bleed resistor for any time that the start capacitor gets kicked out of the electrical circuit this is supposed to bleed off the voltage during the off cycle but you would just check your MFD reading just like any other capacitor it needs to be within these two measurements right here it's not so specific because the capacitor is only in the circuit for a brief period of time make sure to check out our book which is available in paperback and also an e-book form the e-book is available over the website at AC server stay calm as well as a paperback and the paperback is also available at so you go over the port access we go over all the different procedures we use to prepare a system for refrigerant the different vacuum procedures and why you would use one versus another we go over all the different charging scenarios we go over troubleshooting so we go over the different scenarios that you could run into when checking the refrigerant charge on an air conditioning system so go from basics all the way to troubleshooting you can check out the full outline over at ICI citrus tech comm and the links are down the scripted section below hope you enjoyed yourself and we'll see you next time at EC service tech Channel


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