All right, so this is a quick video where I'm just gon na review, some of the realities of checking a heat pump in heat mode. This is a carrier chart. Obviously different brands use different charts. A lot of them use, essentially a pressure chart for checking a neat mode, and the first thing the reason why I'm showing this on the screen is because I want to just reiterate that manufacturer information is gon na, be the best thing to go to.

If you have any access to manufacturer information for checking a system in heat mode, that is going to be best and just to show you kind of how this works, you go to the unit tonnage and then you choose your indoor dry ball. You know the ranges are pretty wide, so there's gon na be a pretty big swing and you can do what they call interpolating. So let's say our temperature is 75 degrees indoor and we have a 50 degree outdoor temperature. If you go across, that means that our head pressure is going to be somewhere in the middle between 213 and 243 in our section is going to be somewhere in between 60 and 62.

So let's say our section would be 61 and our head is going to be between to 13 and 243, which is a 30 degree swing, so you take 15. Add it to the 213. Then we get to 28. So that's what you would expect to be to 28 and 61, just an example of how you do that.

So the indoor dry bulb is what you're looking at and because your condenser is now on the inside, and so with the condenser you're not affected by a wet bulb temperature, because you don't create any condensation on the outdoor, though it lists, dry, bulb, /, wet bulb And of those two, the wet bulb is going to be a more accurate number. So if you're able to take your outdoor wet bulb temperature, that's the one you're gon na want to look at because this is factoring in a very high outdoor relative humidity. So if you can get your wet bulb temperature, you know use wet, bulb temperature. If it's drier outside, then you know kind of the high relative humidities that this is anticipating.

Then you're going to choose a lower temperature, because this all has to do with the heat content in the air, so obviously air that is more moist as more heat content associated with it. Now. The kind of the flipside of that is that, while this is going to cause your pressures to be lower, if you have a lower outdoor relative humidity, when you have a lower outdoor relative, humidity, you're also going to defrost less because you have less moisture to bond. To the coil, so it's sort of a trade-off there, but as it relates to checking your pressures just take your indoor dry bulb temperature.

So let's say our indoor temperature 70 degrees, which would be most common, we'll say two and a half ton unit here so 70 degrees and then our outdoor temperature, you know is thirty. Then we would expect to see a two hundred high pressure, forty four suction. This is an older system. This is an older r22 system, so these pressures aren't going to apply.

You have to find the one specifically for the system, you're working on number. That gives you a pretty good indication of what you're gon na commonly find. And then another thing to note is: is that you know when you're charging a system, because it had a significant leak in it. Something like that, you're gon na probably be better off just using the way in method, and then once you weigh in the proper amount, then check using the chart.

So in this case it's 0.6 ounces per foot of liquid line above or below 15 feet. So this system is pre-charged for 15 feet, so you'd weigh and above or beyond from practical standpoint, if you're completely charging a system from scratch, because I had a major leak, it's gon na be best to first weigh-in and then use the chart. If you don't have access to the chart, then the next thing I'm gon na suggest doing is just taking some common lying temperatures, and let me show you something from the website that kind of demonstrates that. So obviously you know this goes without saying that when you're connecting you want to connect to your common suction port, on your low side, most systems, you can still stay connected on the liquid line on your high side.

But on some systems like carrier where the piston is on the other side of the port, then you really need to connect to the discharge line in order to measure your head pressure. First, off you can weigh in the charge great, don't use a system and below 65 don't check it in heat mode. If it's above 65 degrees outdoor temperature, you chicken cool mode, then you check in heat mode if it's below 65 outside. This is another example of a chart.

In fact, I think that may be the same chart that I was just showing you another rule. That's used in order to kind of confirm charge is the hundred degree over ambient rule of thumb, and that simply means that the temperature of the discharge line with the system running without ice on it is going to be about a hundred to a hundred and ten Degrees warmer than the outdoor temperature, and that applies to both r410a and r22 generally, if you have a higher temperature than that, then you're going to look at insufficient charge through the compressor. So you know maybe a restriction or low charge under charge. That sort of thing and if the temperature is lower than you may see over charge or over feeding.

This goes over these rules of thumb and then also you still have an a DTD, rule-of-thumb, 20 to 25 degrees, suction saturation below outdoor ambient, which means, if you take the outside temperature subtract 20 to 25 degrees from it. Then that's gon na give you what your suction pressure would be, because now you're of a protocol is outside a leaky pump. That means, if it's 50 degrees outside that your suction saturation would be between 25 and 30, and we have a CTO, a condensing temperature / ambient, which is generally gon na, be you know, 30 to 40 degrees, condensing temperature over the indoor dry bulb. This is because of a particular are fairly small condensers, and so you do have higher head pressure than what you're gon na see in cool mode and so 30 to 40 degrees.

Higher it's going to be pretty common will vary, of course, based on the size of your evaporator coil. So if you have a high efficiency of a protocol, then this number will be lower. You'll have lower head pressure and then you can also check it without gauges and we give some guidelines. Your discharge, vapor line, will be 100 110 degrees / outdoor temperature.

Your suction line temp will be 5 to 15 degrees cooler than the outer air temperature. So that's taking into account your DT D, plus your superheat, and your liquid line will be 3 to 15 degrees warmer than the indoor temperature delta. T indoors will vary wildly depending on your outdoor conditions, and so all of these in heat mode are going to fluctuate. More than what you see in cooling mode, because the design conditions vary more so the condition under which that evaporator and condenser are gon na be under have a wider range of variation than what we're typically gon na see in air condition is something kind of get Used to when you're working on heat pumps, but to start with for charging a system from scratch, I would say start with.

We know weighing in the charge based on your line length than your factory charge and then go to using the factory charts and then use these rules of thumb only if you're in a pinch, hopefully that's helpful thanks for watching.