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## cold plate refrigeration

Hi all, I mainly did residential and light commercial ac/heating since getting out of rhvac school in 1987 and took a maintenance job for the last 15 years to get out of call outs and work 7-3 daylight,weekends off. I've learned alot including some ddc building automation since we can log in to the computer to check our different buildings temps,statuses,ect.
I 'm learning alot of refrigeration from water coolers to walk ins but I need some help on cold plates in our various kitchens.i.e seco 7120163, nsf4cm, has a tecumseh mn-ae700at-939-p2 compressor 10psi suction pressure, 20 f superheat.
These units use a temp. controller with the sensing bulb mounted somewhere up in the evaporator tubes that run under the stainless cold plates.the girls are required to keep the food at 38*f ,and they set the stainless pans of food on top but their held up by the rims of the pans and there is a air gap between the bottom of the pan and the cold plate.

I recovered the refrigerant out of the one in question and weighed the 11 0z charge of 134a in after a 500 micron vac just to take that variable out of troubleshooting these units for the other tech was adding /removing refrigerant in past so I wanted to start with the correct charge.
A 10psi suction pressure is 7*f evap. temp. so given the above information I would appreciate some of you refrigeration pros to give me some help on how to set the temp. controller up to a starting point to try a maintain a product temp. of 38*f.The johnsons controller is adjustable from -20*f to 100*f and its one that is high event minus differential is low event. just to make sure I'm looking at this control right high event= cut in, low event= cut out? so if thats true it would be set up as to turn on when the high event temp. at the evap. is reached then you would take that high event temp minus a diff. setting subtract to get a low event temp which would be the cut out temp.

sorry for the long post , but after reading threads from icemeister,duwadda, market tech just to mention a few I know this is probabaly easy stuff for you guys. I am starting to like refrigeration alot and even thought about getting back in the field just to work with it rather than a bunch of different maintanance tasks. appreciate any comments , thanks guys.

2. First off - the "girls" should be closing the lid on the make table when it is not in use. These type of set-ups aren't the most efficient in the world and any help the product can get goes a long way.

Is the product unloaded from the upper rail daily and stored in a walk-in (or in the cooler below) overnight?

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Market tech, They unload to walk in every day. this is for salad bar stuff,fruit , lettuce,cheeses,ect. and some cold plates get lids and others do not, their used so much.

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Get the product closer to the plate. Example: Depth of C.P. 10" using 4" pans are too shallow. Use 8" deep pans and keep product stirred from the bottom.

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I know its probabaly hard to determine on a cold plate unit but I 'm trying to grasp pressure /temp. relations for example: if a evaporators suction pressure is 20psi which equals 22*f 134a,what do I need to set my pressure control to to maintain a certain temp. I'm thinking you can only do this with units with a evap. fan,like if you want a box temp. to maintain 36*f- 40*f pressure control setting to cut in at 33psi approximately,and cut out at about 19 psi with a 15*td across the coil. with the cold plates working from convection is there a target evap. pressure/temp. I can set up and know that my evap. temp. got to be like 35 or 40*f colder than I want my product temp. being no forced air circulation? if they would keep lids on the product,I know that the settings would have to be different with the lids off.

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