I wanted to talk about safeties overloads things that are designed to protect the equipment. I don't think this comes up a ton with us, but it's always a principle that i want us to clearly understand and the easiest thing to kind of start with is a float switch, because we all know how a condensate, overflow switch or a float switch works Right a float switch, but most of us do. Okay, the purpose of it is what what's the purpose of a float switch to kill power to the system. If the system has excessive water, if the system is overflowing water, the purpose is to kill power to the system.

So what does a switch do in order to shut off the flow of electricity in order to keep something from working? It opens right yeah, which is again for somebody who's really new. That kind of is confusing because you open a door to walk through it. You open a faucet to make water flow, but the easiest way to think of it is a drawbridge right. You have a if the bridge is closed.

The cars can travel over it if the bridge opens the cars can't travel over it. So the way you draw a normally closed switch, meaning a switch that's closed during operation during normal function is like that. That's a closed, float switch! That's when there's no water in it right, but then, when water enters the switch opens. So as this level comes up, the switch opens, and then it looks like this right and that's because the water forced the switch open.

Everybody buy that. Okay, so here's where i'm going with this, if you walk up to a system and it has an open, float switch, you wouldn't just say: oh well, it's a bad switch, replace the switch. Would you what would you do check to see if there's water you check to see if there's water in it right so you'd first see? Is there an active cause? Why why is it open, that'd be the first question well and the assumption would be it's open because there's water in the flow? That's what it's there to do. Everybody understands that that's fairly obvious, but let's say you come up to a system and the float switch is open.

You check it and there's no water in it. Now. What do you say? I was trying to cockroaches microswitch. It was actually lifting up the flow.

What was he was he just sitting in there and he was just doing it on purpose just to screw with you that guy's, like that kid's a character man like oh, i see you in there you little knucklehead you get out of there. You get out of there it's kind of the relationship i have with the roaches in my house. I generally call them my children, but anyway uh. So if you come up to a float switch and there is no water in it and the float switch is open right.

So it's here, there's no water. You check with an ohmmeter, it's not ringing out, there's no path! Whatever. What would you do? You'd say it's a failed switch right, but here's the trick to this question if the switch is failed open what likely happened when it failed open? It was open right because the switch doesn't start close, sit closed, its whole life, just honky, dory just sitting there. I am closed.

I'm closed. I'm closed, i'm closed and then one day just be like. Ah you know what i'ma be open now right. That doesn't happen.

What happens is, is it opens and then, when it goes back to close, then it breaks right. It's just like a door, it's like a door that nobody ever touches nobody's ever touched. The door nobody's ever tried to go in and out, and then all of a sudden it just falls off its hinges. Right not likely it's more likely that you have teenagers in your house and they keep slamming the fricking door all the time, and then it falls off its hinges.

Right, that's much more likely if a float switch fails open. It's likely that it's been going open and closed a lot and if there's no water in it now it's likely that there was water in it before so. The first thing you should do yeah. If it's stuck open and it's broken, you got to replace it, but try to figure out why odds are that the thing's been overflowing and just kind of consistently having an issue.

Now, that's actually not the best example, but i'm using it as an example, because it's one that you can get your head around really easy right. A float switch just doesn't fail open. Let's talk about some more common ones and again i just draw the symbols. While i'm doing this because it helps you get used to seeing these symbols when you're looking at diagrams - and it just kind of helps, helps you pick it up, it doesn't really matter to the story.

I'm telling, but let's talk about a thermal limit. Now a thermal limit can sometimes be called an overload. That's what it's called, typically with a motor or in the case of a gas furnace or in the case of heat strips it's just literally a thermal limit, a thermal, a thermal shut off. What do you think? A thermal shut off is something gets too hot.

It opens right, gets too hot. It shuts off. An example of this is when you put a surge protector on a piece of equipment that surge protector, all modern surge protectors are called tpmov. Mov stands for metal oxide.

Barrister, that's how a surge protector works. That's the technology, but the tp part is not toilet paper. It's not halloween. Okay, i know burt was thinking that no, it's thermally protected metal oxide barista and the reason that it does that, if you've ever seen, some old photos of some uh, some of the older types of surge protectors.

Where there's like a big flame on the side of the house, where, like melted, the siding on the side of a house, that's what used to happen a lot with surge protectors is they would go into thermal runaway. It would start shunting current to ground, which is how they work when there's a lightning strike or something, but then they would get stuck doing that until the whole thing just melted down. A modern surge protector has a thermal limited, and this is how a thermal limit is drawn. It's normally closed, but then, if it gets too hot, this is the symbol kind of for a for a thermal switch.

If it gets too hot, then it forces the switch open. What are some common ones of these that you see? I just mentioned one, but what are some others? High limit switch on a furnace? That's a good one. Compressor overload that's another one, any others could be in some cases. It's going to be a fusible link.

A fusible link isn't drawn like this. A fusible link is drawn something like this, where it kind of goes like this. That's pretty bad drawing of it, but that's just kind of a standard fuse and actually what's interesting, is - is that even a circuit breaker is a version of this. Even a fuse is a version of this or this it's just that with a fuse when a fuse blows, it's done right, it's one and done got ta replace the fuse.

So it's not just a switch opening. It just goes and breaks. I kind of liked how i did that i, like the noise i made too, and it breaks so in a in an old fuse box from a generation ago, when they didn't have circuit breakers every time a fuse would blow. You would have to go out to your circuit panel and you'd have to replace the fuse nowadays, it's like this when that breaker overheats or has a magnetic overload either way it opens the circuit, and then you have to reset it right, but it's all that all The same philosophy in most cases circuit breakers are thermal, meaning they actually trip when they get too hot, which is why, coincidentally, you get more trips and circuit breakers on really hot days than on cooler days.

If one of these does trip on you, you show up to a gas furnace and you have a high limit or a roll out a roll out. It's another version of this, a rollout switch and it's tripped or it's failed. It's open. What's the first thing, you should think why? Why is it open? Not, oh, we need to get a new high limit.

Okay or we need to get a new fusible link. You may have to get that once you figure out why, but do everything you can to figure out? Why, before you just replace a part, especially if we've got to come back because if we've got to come back, we want to come back and fix the entire problem. So let's talk about a high limit on a furnace. Okay, high limit on a furnace is just inside the furnace and if the air traveling through the furnace gets way too hot, it opens up right.

So what are what's a reason why it could get way too hot inside the furnace airflow airflow would be the number one reason and what are some obvious things that you check when you have an airflow problem, filter air filter, coil, blower, coil right now, oh and Now somebody might say well that doesn't make any sense on a gas furnace. The furnace is down here the coils up top exactly if the coil is restricted above the furnace. That's also going to affect the airflow when it's in furnace mode right because it's blocking the airflow through the furnace. So a lot of you don't think about that.

Well, my heating airflow is also affected by a dirty evaporator coil, just the same as cooling airflow. You want to think through all of the causes. Let's talk about a compressor, because the compressor thermal overload same thing looks the same way on a diagram. What could cause a compressor to go out on thermal level? Well, first off: what happens when a compressor is out on thermal overload if that's open inside the compressor? What does the compressor do? Doesn't do anything right, so you show up, and what do you find a hot compressor, zero amps? You still have 240 going to your compressor, but zero amps.

First thing: you notice, though, when you walk up to the condenser is what probably not you can't hear it you're going to notice that the fan's running it's not blowing any hot air off the top, and you can't hear the compressor and that takes some perception. Somebody who's completely new or a customer they're not going to perceive the difference because they still hear the sound of air. But you don't hear that deeper noise of the compressor running inside the unit. What are some reasons why a compressor could be out on thermal limit? Dirty power can be, can be villages failed, fan, motor, failed fan motor would be a big one.

So if you walk up - and you don't hear anything - you could have them both off because of a fan motor being failed. So you walk up, fan, motor's off and then you might ever so often hear the compressor start running and then it shuts off again because it's overheats because it doesn't have the fan motor to reject sometimes you'll, have a compressor. That's on a temporary thermal limit. Just because it has a failed capacitor, a wiring issue, you know this because if you walk up to a system that has a failed capacitor, what will you often hear? Don't answer exactly here? Why doesn't it just go and then just melt? It's because the limit takes it out right.

Why does it do it so often because you'll notice it'll go and then 45 seconds 60 seconds later it'll try again. What's that say it again, it resets! Why does it reset so quick, it's not as hot the heat is isolated to the winding and the winding is very thin, copper wire. So it's an electrical overheat. That makes sense it's an electrical overheat because it can't run it's on.

What we call locked, rotor compressor, is bound up, and so it does this like. No, i don't want to move. I thought that would be funnier it wasn't. That was bad when doing maintenances you barely bump, the float switch will cause it to run backwards and they'll overheat.

Yes, it can yeah short cycling alone can sometimes cause it to overheat right. But when it's isolated to the winding, it will reset more quickly and you put the right capacitor in now, it's no longer locked. Now it can run now. You don't have the thermal overload anymore, so you wouldn't want to go up to a system where the compressor is going be like.

Oh, hey, it's going to thermal overload need a new compressor thermal overload's inside the system, so just new compressor right. Obviously, you wouldn't do that, but let's say you go up to a system fan motor is running. Compressor's. Quiet compressor has zero amps.

Now what do you do? Well, you got ta check to see if it's hot or not. So if that's the case first thing, i'm gon na do is pull the quarter panel or side panel off i'm gon na inspect the electrical components and make sure that there's nothing obvious going on there check the capacitor check the start gear. All that, then, i'm going to pull the shut, the power off, i'm going to pull the top and then i'm going to just tap the compressor, i'm not going. To put my hand, oh my gosh.

This is hot, my hand is melting. You know not that kind of thing just tap. It may see if it's hot, if it's hot, to touch. What does that tell you it's a fairly obvious thing: it tells you it tells you that it's been running recently.

It's not just failed just magically, since it stopped running last. It's been running, a compressor being hot is actually a good sign in terms of it, you being able to get it running again, because it means that it has been running not long ago. It just got way too hot. What's the most common cause of a compressor getting way too hot, no refrigerant or very little refrigerant, insufficient refrigerant, but not insufficient refrigerant in the system necessarily insufficient refrigerant moving through the compressor, but what's another reason there could be another cause.

That's actually the opposite: it could be overcharged could be way too much refrigerant could be a condenser coil that is completely packed full. The reality is, the compressor gets real unhappy when it has poor compression ratio high compression ratio, meaning that if the head pressure is way too high or if the suction pressure is way too low. Both of those things make a compressor unhappy, and the worst case scenario is if the suction is way too low and the and the head pressure is way too high. Also, the temperature of the return gas can also affect it.

So systems that have very high return. Gas superheats are going to be more likely to overheat with long run times, so those are all things that you would want to think about. What's the next step you have to take when you feel that hot compressor cool it down right? Who has those sepco magnets with the hose that go on the hose? Only a couple of you anymore, they're, pretty cool right. You can hook the hose up.

You stick it to the top of the compressor and just let it let it go. You don't have to run like super high flow rates, just trickle some water over it. Now some people will say: oh, my goodness, you're going to damage the compressor with that. It's in the rain all the time you know like it's, not the thing is designed to have water running over it.

That's not a problem. Some people will say well yeah, but that shocks the compressor. Whatever look in real life. We've got to get this thing cooled down as quickly as we can, because we got to figure out what's wrong with it to move on to the next call.

The customer doesn't want you saying all right i'll come back six hours later and let you it's one thing: if you're working on a facility like a cubesmart where you're going through maintenances, you find one overheating. Well then, just shut it off and come back later right that would be fine or if you're, a facilities. Engineer and you've got a ton of units and it's not affecting the customer. But if you're there on a service call where you drove there and it's a residential customer, you need to get it cooled off and the right way to do it is to run some water over it.

Now, how do you know when it resets? What you can do is you can actually - and this is this - is a trick that i think eric melli taught me. You take your meter, you put it on ohm scale with the ringer on and you take it and you put it right on your contactor across the two legs now, a lot of guys will be like well that won't work, because it'll just ring all the time. Actually, generally generally, your condenser fan motor, especially well, because you probably have the top off anyway, but generally your condenser fan motor is high enough resistance that it won't make your meter ring. But your compressor windings are low enough resistance that as soon as it closes, they will start to ring.

This is kind of a senior tech tip, because i always did it where i had to stick the meter down in there. But the problem is your leads. Aren't long enough and now you're getting your meter wet or you're running the risk of getting your meter wet. So if you keep it, we actually tested on the carry units out here, and that is actually how it worked.

Do you know that? Because you were there weren't you, no! You taught me that when i never started really mike taught me that too yeah we yelled at him. Well, no! No! No! No! So he described watching watching the resistance come down to a certain point, but yeah right and there's that, but there's also diagnosing a compressor from up top. That's not what i'm suggesting, because i want you to visually inspect the terminals. That's not! So i'm not saying don't visually inspect, i'm just saying when you're waiting for it to reset it's easier to keep your meter away from the water and have the ohmmeter hooked up and then just listen for it to start ringing than it is uh to have your Meter down on the inside down by the terminal, so you guys get what i'm saying generally: okay, it's! This is kind of a complicated thing, but the point is: is that you figure out what caused it? You don't just cool down the compressor and say all right.

It's cooled down now: now it's working great could be dirty, condenser could be high head pressure because of overcharge could be that it's low on refrigerant could be uh metering. Device restriction could be a line, dryer restriction, anything that's causing either not enough compressor to make not enough refrigerant to make it back to the compressor or too high of pressure leaving. The compressor can cause that issue kind of like that motion. It's like this or like this, like that, you know we keep doing that.

Yeah, okay, good, always figure out the cause. That's the point now. Another type of safety we have a low pressure switch looks like this. So that's what a pressure switch looks like that's.

What a thermal switch looks like and a float switch is just a circle right and then we have a high pressure switch. Do you distinguish that? Can you see the difference between these two? So this one here opens the high pressure switch opens when the pressure increases the low pressure switch. Well, this is kind of opens when the pressure decreases, loss of charge switch same way. Pressure decreases enough opens shuts off the system.

So if you find a pressure, switch, that's stuck open. Well, the first thing to figure out is: is it currently in that condition if a low pressure switch, that's open? What's the first thing you do check your low pressure, see if it's way too low and then maybe that's why it's open but see you check it and it's not way too low systems off pressures are equalized and they're what you would expect as far as sanding Pressure, you would say yeah the low pressure switch is keeping the system off. So i have a failed low pressure. Switch first thing you check would be your connectors check, your wires make sure they're not broken, but then at that point you would jump out the low pressure switch and figure out why it went out on low pressure in the first place, because it's probably low on Charge or has a restriction or something that causes it to go off because again, safeties don't fail in the opposite position for no reason, just like a door doesn't fail.

If somebody didn't open it or close it or slam it. What what are some things that would cause a high pressure, switch to open high pressure, failed condenser fan motor, in which mode we're so on a heat pump in which mode in cool mode a failed, condenser fan motor would cause a high pressure switch to open in Cool mode, what's something that could cause a high pressure, switch to open in heat mode, blower motor? What else? That's the only thing overcharge what else dirty filter dirty filter? What else high pressure switch pretty unlikely, and that goes into a complicated topic about restrictions and what happens when a system is restricted but possible unlikely? What else you just said, the exact same thing: twice: evaporative coil, dirty, okay, stop being like this low water flow on a pool heater for sure. Now again, not a lot of systems have high pressure switches, but where's the place that we have a lot of high pressure switches that we do a lot of maintenances on as in right now, yeah sophisticate. This decay does have high pressure switches and if you were to find a system with a trip, high pressure switch right now.

What would be a possible cause? Running heat mode when it's warm outside could be, could also be running in heat mode and there's some sort of indoor airflow issue. Indoor airflow issues in heat mode cause high pressure trips because where's the condenser in heat mode inside right. So now, airflow over the inside coil results in high head pressure. Now it could be either way because it's switching back to cooler heat, so it could have tripped either direction, and one unique thing about lennox is that it has this lockout if it goes out.

So many times the switch may even close again, but it still stays locked out and that's where you pay attention to the board blinky blinky board. Right now on linux, the most likely cause is what of a high pressure switch lockout trip on those linux heat pumps. At cassiola condenser fan right because those condenser fans, a lot of them, are those older, clamshell condenser fans that just don't they don't last as long and so then they'll intermittently work for a while, then they'll, overheat and shut off, and if the condenser fan shuts off The compressor may overheat, but it may just keep going out and likely will keep going out on head pressure until that thing trips enough, that it locks out, and you show up turn it back on and everything works, because now the condenser fans cooled off again now It runs again, i don't know what caused it and then two o'clock in the morning with the call again it's doing the same thing that eli doesn't know anything. He looks like the unabomber.

I don't know why they always say that they do it's a weird thing that they always say: don't send that guy back all right, any questions about any of that. So the so lesson is switch opens switch. You know it opens for a reason, figure out what caused it to open before you replace it, and also with thermal overloads. It takes a lot longer with a compressor, especially because of the thermal mass, when there was a refrigerant reason for it to overheat.

A lot of times it takes a lot longer for that to reset than you would ever think, but if you walked up and it was hot, it will reset. So don't do the whole thing. Well, i guess it just won't reset it. It will reset.

So just keep letting it cool until it does. It will sometimes be cool to the touch on the outer shell. It could still be hot on the inside yeah yeah, i mean you got ta, give it a couple of minutes and you it'll be all hot yeah right. You have to yeah so unhook the refrigerant pipes, spray water through the compressor.

It's not funny because it'll happen. Uh another thing that i wanted to mention quickly because sam said that you need to pinch off compressor, stubs and braise them. How do i, how should you remove compressors and line dryers? What's the best way to do that, cut them out? If you unsweat, you are likely to get a little fireball coming back at you, so it's a safety issue, but even more than that with compressor stubs, you may or may not know this, but compressor stubs are generally copper plated steel and if you try to pinch Them a lot of times, you're going to start breaking that copper plating off and now, when you try to braze it regular braze rod isn't going to hold because regular foss, copper, braze rod the stuff we use all the time, whether it's 15 or five or zero. Doesn't matter it will not seal up steel so now you're stuck with using 45 in the flux or using the flux, coated really expensive rods.

So it's better to cut it out. So now you've got a stub, a copper stub pinch. The copper stub, then brace that with your regular 15 or whatever you happen to have in your truck, make sense. So leave a stub pinch, the stub don't pinch the actual port on a compressor.

If you can help it and if you are going to pinch support on a compressor, because that's your only choice, then i would suggest using just go ahead and just use the higher percentage. Uh silver, even better, would just be to go ahead and put a stub in it and then break then pinch. It then brace it great. Thank you all have a wonderful week, thanks for watching our video, if you enjoyed it and got something out of it.

If you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel and click, the notifications bell to be notified, when new videos come out, hvac school is far more than a youtube channel. You can find out more by going to hvacrschool.com, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more. You can also subscribe to the podcast on any podcast app of your choosing. You can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching you.