We cover why a TXV goes fully open when there is a vacuum or no refrigerant in the system- we cover the txv forces including the bulb and and external equalizer
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A question that comes up a lot from technicians is this question of hard shut off, txvs or non-bleed txvs, and whether or not you can pull through them during evacuation or during vacuum, and so this applies to both when the txv is under vacuum or when it Has no pressure in the system at all, so this image kind of shows it all in one place here, we've got the pressure from the bulb on top. We have the pressure from the external equalizer going underneath the diaphragm, the diaphragm drives a pin of some sort and again not all valves. Look exactly like this. This is just an example valve to kind of give you the idea, and you have the force of the bulb and the force of the external equalizer and then the force of the spring, which assists the external equalizer in closing.
But when you have no pressure in the system, you have no forces from the external equalizer, which makes the force of the bulb greater on top of the diaphragm, and so you can see here p1 force pressure above is greater, which forces the valve open. You do still have a spring force and so there's going to be some force being pushed back. But the valve is still going to go to its maximum open position, especially when the system's off. Because when the system's off you're also going to have a warm suction line, so you're going to have high pressure in the bulb and then you're going to have no pressure in the external equalizer and that's what drives the valve open all right.
So we're going to show kind of all three positions here: first, under normal conditions, you have liquid refrigerant flowing into the valve and then it's being metered when you have a case where the system goes off and now the external equalizer pressure is greater than the ball Pressure, then, that valve can go completely closed, so that would be a hard shut off position, but in cases where you have a greater bulb pressure than your external equalizer pressure like cases where you're under vacuum or the system is off in this case, the pressure above The diaphragm is greater because you have maximum bulb pressure, but you do not have the pressure in the system in the suction line to work against it. So now that valve goes completely open, even if it's a hard shut off valve, meaning it's a valve. That's designed to go closed in the off cycle when the system has refrigerant in it like in the case shown here this matters because of the one hose setup. A lot of people get confused about the one hose vacuum setup like we're, showing here in this fly through when you connect to the suction line, with the hose, as shown here and your micron gauge, or your vacuum gauge is connected to the liquid line.
A lot of people will note that you're pulling through the expansion valve and they see that as a problem, but keep in mind, though there is some pressure drop across the expansion valve, and this is not the very fastest way of doing it. That valve is going to go wide, open and under most circumstances, where you're only pulling on the line set in the evaporator coil you're going to find this to be a very, very fast method of connection. So long as you have your schrader pulled on your suction line, as shown here, so that's it. That is why a thermostatic expansion valve a txv or tev or tx valve as some people call it. That's why it goes wide open when the system is under vacuum or has no refrigerant in it. You have a bulb force, that's overcoming the absent external equalizer force, thanks for watching we'll catch you on the next video.
What about a EEV? Does it go completely closed or open, when in the off cycle or also when there is no pressure. I do understand that its not controlled the same way but was just wondering how that works maybe you could do a video on it.
I would think it would act like a non bleed txv. If u could Shed some light that would be nice. Thanks Brian .
Excellent video. Can anyone tell please "how does the Valve close when system is shut off"?
Thanks. Service area Orleans??
Never gave a this a thought before…fascinating
This will also show you if you have a stuck txv. From the vintage of rust inhibitor treated compressors and the buildup on the needles. Spent a few hours last night testing my nrp8di against my company 4 cdm jb. It's all about the hose. Wish I was better with the gopro. One day.
Very well explain, tank you !…
This really helps, thanks. Your videos are great and the animations make it easier to understand. I appreciate the hard work you put into these videos and the detailed explanations of exactly what it is going on inside the system. You’re videos have taught me more than school ever did lol
What about hpr valves/headmasters. I've also wondered why if you loose the charge in the pig tail for hpr valves it doesn't go into bypass but goes into the "normal" operating at position.
How about EEV's?is it the same?
Great illustration btw 🤩 Are you in Kanata ?
Loving these excellent quality illustrations!
How can you pull a vacuum, the caps are missing on the Navac vacuum pump tee in pictures LOL, great video still.
Great Job Sir excellent explanation👏 Service area Ottawa??
That is an excellent explanation! I use the same set-up to evacuate the system every day, and sometimes I wondered the same thing. What if you're pulling a vacuum on an inverter-type unit, like on a Carrier Infinity system? When new, the refrigerant is isolated in the compressor but if you need to do some repairs, since they have an EXV on the condenser side?🤔
Thank you for this explaination. Just to be sure, is it the same in case of refrigeration systems which are controlled by 'pull down' method, right?
Just pull vac on both sides, problem solved.
Have you heard that you shouldn't just hammer the liquid line valve open while system is under deep vacuum or it could damage the valve?
I would dare say that the vacuum acting under the diaphragm would actually be working to open the valve
I literally think about this every time I pull a vac. Now I can have an answer thank you!
How about a indoor TXV causing high pressure cutout in heating mode, within 3mins. Had manufacturer argue that it wasn’t indoor TXV causing problem, replaced outdoor TXV, they sent new condenser, finally they sent indoor coil with TXV. It wouldn’t bypass fully and I kept telling them it has too much of a drop. 12° drop across indoor TXV. Are you in Barrhaven ?
Great info. Thanks.
Beautiful
Very nice illustration. Very monotonous voice that's why hard to follow
always great
Kudos on the the illustrations and explanations!
Can you do a video on what happens to a piston under vacuum?
Very straightforward and great illustrations. Thanks for another quality video Bryan and Crew 👍