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Eric Mele tours a motor room for Emerson direct expansion (DX) equipment with two medium-temperature racks with remote headers. DX systems use a typical compression refrigeration cycle to accomplish cooling.
The remote headers for each rack are placed along the motor room walls, not within or immediately beside the racks. Each rack has multiple compressors that discharge compressed vapor into a single common discharge line. The discharge line leads to the oil separator, and then it leads to the heat reclaim or condenser.
The oil separator has an oil line that leads to the oil reservoir. The reservoir stores oil until that oil needs to make its way back to the compressors. Then, the oil passes through an oil filter and heads to the compressor. Each compressor has an oil regulator with a sight glass to ensure proper oil feeding.
Stemming from the discharge line on rack 5, there is a smaller line for hot gas defrost. However, the defrost isn’t used on that rack.
In this particular system, the air conditioner’s heat reclaim is a reheat coil, which also helps with dehumidification. Then, another line leads back to the rack and forces the refrigerant through a check valve, which leads to the condenser. On the second rack (rack 4), half of the condenser has been eliminated, which we can see on the piping and when we go outside.
From the condenser, you will find two liquid lines with check valves. In some cases, a rack will have a condenser split valve, but the rack in the video does not have one. The refrigerant in the liquid line goes to the receiver (with a liquid level indicator) and then the filter-drier. Once the refrigerant passes through the drier, it travels all the way to the remote header, where the liquid header is. The suction header is on that same remote header and may not have a suction drier.
Each evaporator has an electronic EPR valve to throttle the suction pressure and maximize runtime. Those valves close during defrost. Then, the suction header extends all the way back to the rack and the compressors on it.
The other rack has a defrost differential valve. That valve creates a pressure differential to establish the flow of hot gas through the defrost header (on the remote header) and up the liquid line.
On this equipment, the compressor contactors are behind a panel on the rack itself, and each contactor has its own control breaker. The controller is also on a panel on the rack. You will find the relay board behind that controller
The defrost board is behind a panel on one of the remote headers. The schematics are behind that same panel.
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This is eric with halo services and hvac school and we're going to do a little walk around of this dx motor room. While i wait for this unit to defrost, we got two medium temperature racks in this room. We got remote headers. This is the header for this rack, which is rack five.

This is the header for this rack, which is rack four. Obviously, you've got your compressors, they all discharge into a common discharge line, and that goes over to your oil separator this guy right here and from there we can send it to our heat, reclaim or condensers. So back here. This would be your hot gas defrost, but it's not used on this rack, so we have discharge line, go into our heat reclaim, which is, i believe, for the air conditioner reheat coil on this rack, that's coming back.

This other line is coming back through a check valve here, and then these both go to your condenser. Both of these lines go straight to the condenser, and these two come back. These are both liquid lines with check valves now, sometimes you would have a condenser split valve, but this does not have it on this rack. So then it goes straight into the receiver out the receiver into the dryer and then here's your liquid line coming out of the dryer back up and over to your remote header.

So this is your remote liquid header for your circuits out front, and this is your remote suction header, coming back suction, dryer, there's, probably not one in there, because i usually don't want to run them at least not permanently and then on. All of your evaporators you've got electronic epr valves. There's different names for these. This throttles, your suction pressure, to keep it higher on the case side, so that we can achieve 100 run time for the cases and when we go into defrost that will close.

So your suction header comes back to your rack down and around back to your compressors there coming out of your oil separator. You have your oil line at the bottom of your separator, which feeds your oil reservoir and then goes through your oil filter and out to your compressors to each one of these oil regulators, which should be adjusted for like a third to half cycles for proper oil Feed to each compressor there on the front, you have your receiver, your liquid level indicator. These ones vary a lot because that ac heat reclaim takes a lot of gas when it's active, so they'll go anywhere from 10 to 40 percent and back and forth. You got your same deal over here, except this rack has hot gas defrost.

So you see this valve here is a defrost differential valve. You go to this rack. We don't have that so on this one. This valve will create, like a 20 to 30 psi differential, depending on where exactly it's set when something's in defrost.

So it can establish flow of hot gas through the defrost header and back up the liquid line and that refrigerant will merge with the liquid back at the liquid header here. So when this goes into defrost, it's hard to see here, but there's your defrost solenoid, the defrost solenoid, and it ties in down there below this eepr valve. This will close defrost discharge. Gas will go down the suction line and come back up the liquid line and into the liquid header, it'll, probably be a liquid at that point, at least that's the idea.

So that's, basically your only difference there on these racks other than that they're, pretty identical. We'll look in here: here's your compressor contactors each contactor has its own control breaker, so that one problem doesn't take down the whole rack. Here is your controller. In this case, it's an emerson controller hold on.

I got ta pop this open and that controller goes to your relay board and those relays are assigned to different actions like the screen compressor. I don't know how well this shows up compressor, one two and three master hot gas, which is that ddr valve that defrost differential valve you can see here we got some stuff. That's crossed out um the condenser split valve, which just doesn't have so you got different outputs there. Motor saver for the whole rack this one's going to be similar.

It looks like some of these have been modified but pretty much the same thing. Compressor contactors in the other panel, here's your defrost boards. These are controlling all your eepr's and your defrost, so you've got your schematics and everything we're not going to go circuit by circuit, because it's basically just controlling all these. Of course, you've got exhaust fans and air intakes to keep the motor room full.

You have. Your main breaker panel got more relay boards in here. As you can see on this rack, somebody has eliminated half the condenser at some point. So if we go outside, you can see this half of this condenser has been eliminated, for whatever reason those two are still in circuit.

We've got some acs. You got your low temp, i think there's a low temp and medium temp over there. We might go. Look at that in a moment, but that's pretty much 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, 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. You can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching.

16 thoughts on “Supermarket dx motor room walkaround”
  1. Avataaar/Circle Created with python_avatars leslie orm says:

    Looks like a Publix

  2. Avataaar/Circle Created with python_avatars Tyrone Sheppard says:

    I noticed the rack had no mechanical subcooling
    heat exchanger on the liquid line just before it leaves the rack and heads into the store to the cases.

  3. Avataaar/Circle Created with python_avatars Nikola Patrcevic says:

    That room is f*cking dirty… man…

  4. Avataaar/Circle Created with python_avatars Derrick Hudson says:

    Thank you for posting, it helps me more then you’ll ever know just to learn the terminology in the field 🙏🏼it’s a wonderful base to work up from

  5. Avataaar/Circle Created with python_avatars Roger Bettencourt says:

    Nice walk through. Thanks.

  6. Avataaar/Circle Created with python_avatars Paul Garas says:

    I severely miss working on these guys

  7. Avataaar/Circle Created with python_avatars InsideOfMyOwnMind says:

    As impressive as the hardware is, NASA only had an infinitesimal fraction of this computing power to go to the moon.

  8. Avataaar/Circle Created with python_avatars CallSign Mayhem says:

    Looks like a Walmart set up.

  9. Avataaar/Circle Created with python_avatars Stuart Milne says:

    Very interesting. Rack headers are a whole different type of ball game than individual dedicated compressors. Service area Ottawa??

  10. Avataaar/Circle Created with python_avatars Carlos Lira says:

    So much respect and appreciation from this residential service tech in okc who watches all your video's. Thanks for all the true field info and the integrity your company exhibits that keeps me striving to learn and be the best I can be in this industry!

  11. Avataaar/Circle Created with python_avatars squirtinb says:

    HP motor rooms. I’d like to make a shuffleboard out of nice oil stained floor some day 😎

  12. Avataaar/Circle Created with python_avatars Blue Collar Rebel says:

    This setup looks familiar 🤔 Are you in Nepean ?

  13. Avataaar/Circle Created with python_avatars Corey Cruz says:

    I know that motor room

  14. Avataaar/Circle Created with python_avatars marty maness says:

    Have fun leak checking that. Lol.

  15. Avataaar/Circle Created with python_avatars james tomlin says:

    Nice 🙂👍 ❤️

  16. Avataaar/Circle Created with python_avatars Eassyheat/ Cooling says:

    That's cool 😎
    Stay safe.
    Retired (werk'n)keyboard super tech. Wear your safety glasses.

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