Eric Mele does a Supermarket DX Motor Room Walkaround 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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21 thoughts on “Supermarket DX Motor Room Walkaround

  1. 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!

  2. HVACR Northeastern says:

    This bring back memories when I started had only 4 years into this trade late 90s work all type racks for about 7 years nationwide Supermarket chains, meat plant, food distributors. Miss the troubleshooting part but not long hours & stress .

  3. Flyby Airplane says:

    Hi, I have retired long enough,,this is the FIRST EMERSON CONTROL PANEL SEEN, ALL units used to have a mechanical clock, with a circuit for each,Refrigeration circuit, PARAGON made the sections, where EACH CIRCUIT WERE REPLACABLE, but there were others where you had to change the ENTIRE CLOCK , FOR ANY THAT WENT BAD. ALCO EPRS, then there were several SPORLAN EVAP CONTROLS, NO LONGER MADE, as NEW ones came out. Here in NOR EAST, HEAT RECLAIM, where you bolted head pressure, using MORE KWS, became EXPENSIVE, so NAT gas DUCT FURNACES BECAME CHEAPER TO OPERATE , the ORIGINAL STOP & SHOP stores were water cooled, and had a HUGH WATER COIL FOR HEAT, you would be really surprised that a 3 ^F. Ted would heat the store !
    But times change, & so has technology, 🇺🇸🇺🇸🇺🇸🇺🇸

  4. Flyby Airplane says:

    There were so many brands of sumarket racks, EVEN MELCO A/C actually made racks, there are/were 2 in NJ. 1 IN A FOODTOWN in HILAND PARK, & KINGS IN MORRISTOWN. ,,LIEBERT cute computer room a/c co, MADE REFRIGERATION RACKS, there is/was the only one I ever saw,,was in a PATHMARK in SOMERVILLE NJ it had some GREAT FEATURES. , I do NOT think they are still made.
    And of course they were ALL. COPELAND COMPRESSORS ! 🇺🇸🇺🇸🇺🇸🇺🇸

  5. modestfreak87 says:

    I’m looking into a career in hvac and this video is overwhelming. At first I was like okay okay I’m trying to follow and then when you got to all the wiring and electrical parts I am now seconding guessing this path lol. Maybe it is simple but I don’t know what I’m looking at so it looks impossible

  6. gearhead0800 says:

    Hello Eric, can you help me clarify something for me ? In this video at time 0:49, you are mentioning the oil separator but your left hand seems to be pointing at a filter/dryer. Am i seeing something wrong?? Thanks in advance

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