Evaporator pressure regulation is how we achieve 100 run time in between defrosts and that can be done with either mechanical or electronic valves. The valve on the right is a mechanical version and you would adjust the stem in order to set your evaporator saturation where you want it and it will hold there, provided the rack pressure stays below that. The one on the left is a electronic version and it's going to reference a temperature sensor in a pressure transducer to maintain a constant temperature, so it will modulate slightly, whereas the mechanical one will more or less hold steady at the pressure you set it at. But the main idea here is: we keep the evaporator saturation more or less fixed to achieve constant run time now, the suction pressure has to be below your coldest evaporator at the main suction header.

In order for this strategy to work so there's usually a little bit of wiggle room, there it'll be a little bit below what you're gon na run your coldest evaporator at to allow for any variation. But that's the basic idea of what we're trying to do is throttle the suction gas to control that evaporator pressure to just maintain a constant, steady temperature on the load, 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.

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