All right, so, let's talk about one of the most common, miss diagnosis that technicians get her confusions that they have about restrictions. A common thing. The techs believe is that if you have a liquid line restriction, say a clogged liquid line, filter, dryer or maybe a metering device, that's over metering, meaning it's not allowing enough flow through it. It's restricted or maybe even a service valve.

That's you know not open. All the way, for example, they think that you're gon na have higher head pressure and the idea they think that okay, well, this refrigerant is gon na, come into the compressor. It's gon na back up against this restriction and that's gon na cause high head pressure in the condenser. But if you look here at this, our freshener diagnostic quick sheet that I've made it shows you right here that your suction pressure will be low.

That's sort of the defining characteristic one of the first things that Tech's always look for is low suction pressure and your head pressure is actually gon na be normal to low. So, what's going on there, they think well that doesn't make any sense. There's no reason that your via restriction here and you're measuring here on the liquid line, why on earth would your pressure here be lower than normal when it comes into a very simple principle, two things two analogies that I'll give the first is dangle refrigerant has maybe 25, pounds of refrigerant in it saying r410a tank 25 pounds refrigerant in it which could charge. You know to the three residential air conditioning systems, and yet the pressure inside that tank is not high.

It's static pressure based on the saturation chart. We know that because there's liquid and vapor present in there well, why isn't it high? You have all that refrigerant in there. Wouldn't you think it would be high? Well, the reason why it's not high is because it has achieved stability with the outdoor air temperature, and so something having a lot of refrigerant in it by its very nature, doesn't cause high head pressure, but you say: okay well, I understand that. But you have this compressor, that's sitting there pumping away and it's forcing him against this restriction.

Wouldn't that cause the pressure to be high. But the thing that you got to know is: is that a compressor it's pulling from somewhere in order to pump out? So if you're not moving or frittering, and therefore you know significant amount of heat down the suction line, then you don't have the refrigerant density. Doing going into the compressor, then you're also not going to have as much refrigerant going out of the compressor, which is why sometimes, when you have a restriction, you'll see that your head pressure go up for a little bit and then it will slowly kind of dive Down along with the suction pressure, and that's what happens when the system essentially pumps down, that's the second analogy: if you've worked in air conditioning we've all pumped down the system, that's shutting off the liquid line here at the outlet of the condenser. You have systems that are designed to pump down both air conditioning and refrigeration, and what happens is you shut off the liquid line or a king valve and then the refrigerant pumps into pumps down into that receiver or condenser? And then it will often you know, shut off on a low pressure switch and that's actually how it's turned on and off that strategy's been used for ever and obviously if it was bad for the system to pump down well, they wouldn't have had systems that pump Down all the time, in fact, it's actually a good thing for the system to pump down, because that helps prevent refrigerant migration into the compressor crankcase.

So it's actually a good thing. Now we have to give a caveat here. There are some condensers that are not designed to pump down today we have a lot of micro channel condensers and they have smaller internal volume and they're not designed to hold necessarily the entire system charge, and so you need to make sure, don't don't pump down a Micro channel condenser, unless you know you should sometimes the condenser, can't hold the refrigerant charge it can be held in the receiver instead of bending on where the restriction is that can affect it. But we're talking about you know typical situations in residential and so we're gon na read this note right here, and it goes along with this liquid line restriction this little star here it says, restriction effect on head pressure varies with the exact location of the restriction, especially If you have receiver system refrigerant capacity, meaning how much refrigerant the system can hold presence of a receiver and whether the charge is correct - and I mentioned whether the charge is correct - because a lot of cases you'll have a restriction - that's coupled with overcharge.

So let's say we have a liquid line: dryer, that's restricted. Technician shows up. He sees that the head pressures low, the suction pressure, is low and he says well, I know if the head and section pressure is low. I'm low on charge by golly grab my tank out start Jack and refrigerant in it.

Well, eventually, the head pressure is gon na go up because, as you fill this condenser more and more and more, the volume decreases to the point that you will start to get hydrostatic pressure and that will start to build up. You'll get you'll get hydro lock, because you have so much liquid inside that condenser. And so then, you can really have some high pressures, which is a real problem, and so restrictions may show high head with short run time or on systems with very small condensers or on systems that have been overcharged. In addition to the restriction, like I mentioned in general, restrictions are in the liquid line and will result in low head after sufficient runtime.

So your most common restrictions that exist out there, liquid line dryers those can be either inside of a condensing unit or outside of a condensing unit. They can either be by the air handler or by the condenser in typical residential applications or metering devices screen inlet screens and metering devices that have clogged up and they're, not allowing enough refrigerant through maybe a bowl, but that's lost its charge, and so the power head Isn't opening the valve the way it's supposed to those are some common constants or restrictions, maybe even a kink liquid line on occasion, it's very rare that you see restrictions in either of these other three lines, and really the expansion line is very rarely even the line Except on ductless systems, your suction line very rarely has a restriction in it unless it has a sectional and dryer, and your discharge line almost never has a restriction in it and, although I have seen it when somebody braces in a compressor and they leave a bunch Of boogers in the compressor and that restricts the flow through the compressor, and that can definitely cause how I had pressure for sure at that point again, it's all a matter of where you're measuring your pressure, so we're measuring them here at the outlet of the condenser. At the liquid light service port, that's where we're typically measuring our pressures on a residential system rubber meets the road. Why does it do this very simple? What happens is when you have a restriction, not as much refrigerant can come through the evaporator and back so your refrigerant density decreases, there's less for your compressor to pump and there's less heat being added to the system, because my favorite name for an evaporator.

If you think of it simply, you know we call them evaporators and condensers, but I think a better way to think about an evaporator is a heat absorber. Your evaporator is there to absorb heat and your condenser is a heat rejector compressor. Is your pressure, increase or and metering device? Is your pressure dropper? So that's one way to so. You have an evaporator, that's your Heat absorber! Well, if you don't have as much refrigerant going into your Heat absorber, then you're not absorbing as much heat, and that means you're not bringing as much heat back to the compressor and if you're not bringing as much heat back to the compressor, then you don't have, As much heat going into the condenser, if you don't have as much heat going into the condenser, then there's less heat to reject and therefore you don't have high head pressure.

Most common causes of high head pressure are going to be high load overcharge so cases where you're, bringing more refrigerant back to that compressor, more heat back to the compressor or if the condenser isn't allowed to reject the heat. So dirty condenser is a real common one that causes high head pressure if you've ever noticed, if you have low load, so you have a dirty of a protocol, you're gon na notice that your head pressure is actually very low and that's because you don't have as Much heat cranked back to the compressor, the density is lower, and so you don't have as much heat to reject in the condenser causes of high head. There's lots of causes of high head most commonly. You know, dirty condensers, anything that causes you.

Don't you don't have. As much heat rejection off of your off of your heat rejection unit here known as your condenser or you have high load, you have more heat coming back in or you have overcharge, but liquid line restrictions very very rarely cause high head. It can cause it for a short period of time, as this refrigerant kind of makes its way back through, but eventually what's gon na happen is this low side is gon na be starved, and when that starved and then the pressure is gon na drop, because you Just don't have as much refrigerant or heat coming back in the first place. Hopefully you found that helpful thanks for watching you.