Compound compression, so if you look at these compressors, you can see the suction line is coming up to the front of the compressor here and it's teeing off to the two heads and then, as you look on the back, it tees back together and there's a couple Pipes coming in here and we'll go over all of them eventually, but this is the discharge from these two heads going into the normal suction in the end bell of the compressor here and then we're gon na have to walk back around to look and see the Discharges are coming out of that head and down into the main discharge header, so the first stage is external and then it gets pumped to the back of the compressor and then through the second stage, and then we're just going up the discharge line and out now These other two pipes on the back. If we look at them there, one of them is a suction line from the sub cooler, so it's actually running at a different suction pressure and the other is the liquid injection for demand cooling. So if we look here, this rack has a sub cooler, so you got your liquid in and then your liquid out and your suction, coming back out from the evaporator side of your sub cooler is right here and it's going down under the floor here and we're Going to trace it back along with that other liquid line, and it's coming up here and down here, so the bottom is a suction down there and the top is a liquid and they're both feeding back into that intermediary discharge line there. The suction gas is coming back there and the liquid is getting shot in for the demand cooling to keep the compressor cool, and it's all coming in in that intermediary discharge line back into the compressor.

So here's some better angles. You see the expansion device element is going down to the discharge line, so it's referencing that in order to start squirting some refrigerant in there and you notice, there's solenoid valves on everything too to control it all so just getting some better angles. The suction header is the bottom. It also has a solenoid, the intermediary suction header and the top again is your sub cooled liquid.

It comes in and tees off to all everything, it's quite a bit of piping on these additional, but the main reason for doing all this is you end up with a lower overall compression ratio which equals greater efficiency. So here's another view of the sub cooler again that suction line again and that's about it 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.

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