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Originally Posted by pecmsg

If I can get small drops of ice forming between the fins and the drain pan I know I have the temp control dialed in perfectly!

<<< My "Modified Like Button".

Originally Posted by pecmsg

Old Beef aging boxes were like that. Fancy ones had 2 or 3 fins per inch!

So those were like a hydronic coil ? This one was just copper lines with no fins.

Originally Posted by VTP99

Wait till you see a gravity coil made by hanging copper lines from a ceiling. I was in complete amazement to see such a thing work for a walk-in.

Old Beef aging boxes were like that. Fancy ones had 2 or 3 fins per inch!

Wait till you see a gravity coil made by hanging copper lines from a ceiling. I was in complete amazement to see such a thing work for a walk-in.

Measuring oz is difficult. Also you cut the cap tube that changes the charge. Someone else may have cut the tube before you. You changed the drier now it probably larger, more charge.

And the last is ........................….A cool compressor is a happy compressor!

Originally Posted by pecmsg

Use the weigh in charge as a starting point, Get the case at or near temp, develop a frost line to the pump and back it off a few inches.

Why is that method better than just going with the factory charge? It seems like that’s a little extra work and labor. What are we gaining?


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If I can get small drops of ice forming between the fins and the drain pan I know I have the temp control dialed in perfectly!

Use the weigh in charge as a starting point, Get the case at or near temp, develop a frost line to the pump and back it off a few inches.

This unit was low after all, the cap tube wasn’t restricted. I ended up pulling the charge, cutting off the first 6” of the cap tube, replacing the FD, vacuuming it down and charging it with the factory charge. It pulled down from 69 deg to 35 deg surprisingly fast. And it ran 8-9psi suction so that must be normal for this unit.

I kind of suspected it was low from the beginning. And then when I vacuumed it and I struggled to get it below 450 microns I was leaning even more towards a leak. The bummer with this unit is it’s totally built in. This was a boutique bakery so of course they couldn’t just set a display case on the ground. They had to build it on a pedestal and box it in with an apron front. It does look really nice but I couldn’t even clean the condenser coil let alone properly leak check it. So I’ll be back another day with a helper to get it out of there and tear into it.


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Originally Posted by TechmanTerry

I was taught slightly different.

A good gravity coil job needs an 1 1/2 -2 hr defrost,as pointed out by pecmsg. WHY? Because the gravity coil job builds ice all day long.Next time you get a chance on a gravity coil,start out by seeing what a clean/clear coil looks like right after a defrost. Then watch the coil as the system runs and cools. Frost builds on the coil and fins.Then when the comp shuts off,watch the frost pattern,watch the frost begin to melt,watch the water just start to drip and hang off of the bottom of the fins,watch the comp re-start and see that water drop re-freeze,over and over and over. Finally as the frost/icicle pattern builds & just starts to block the airflow thru the fins/coil its time for the next defrost cycle. One of the big advantages of a gravity coil is the surface of all of those trays filled w/ mayonnaise laced salads does not dry out and get all ugly looking.

I get that...

True uses that as their temp control along with a defrost clock with 1 to 1 and a half hour periods to allow the water to drain

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Originally Posted by UmmScott

On True units with gravity coils,
They use a constant cut in of 35F and cut out at 15F coil temp at the midpoint setting of the control.

Just a general idea for ya

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I was taught slightly different.

A good gravity coil job needs an 1 1/2 -2 hr defrost,as pointed out by pecmsg. WHY? Because the gravity coil job builds ice all day long.Next time you get a chance on a gravity coil,start out by seeing what a clean/clear coil looks like right after a defrost. Then watch the coil as the system runs and cools. Frost builds on the coil and fins.Then when the comp shuts off,watch the frost pattern,watch the frost begin to melt,watch the water just start to drip and hang off of the bottom of the fins,watch the comp re-start and see that water drop re-freeze,over and over and over. Finally as the frost/icicle pattern builds & just starts to block the airflow thru the fins/coil its time for the next defrost cycle. One of the big advantages of a gravity coil is the surface of all of those trays filled w/ mayonnaise laced salads does not dry out and get all ugly looking.

This is a outstanding Classroom.



I'm taking notes.

I normally shoot for -27/-32’C on gravity coils for refrigeration deli case.
Defrost is important as you do not want the small droplets of water to freeze under the coil as this effects performance

On True units with gravity coils,
They use a constant cut in of 35F and cut out at 15F coil temp at the midpoint setting of the control.

Just a general idea for ya

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Cap tube..Forget LP for control.

ETC digital with the sensing bulb buried in the coil. 25 - 35° differential. (you'll have to play with the diff)

Gravity coils run lower pressures then forced air. "S L O W L Y" Develop a frost line at the compressor and back it off a few inches!

Thanks man. I’m trying to determine if I have a restricted cap tube or low charge. Unit was in a vacuum and I added a few oz but the pressure won’t rise above 10psi (134a). It’s a little bakery case designed to maintain 36-45 deg. Even at the high end of a 25 deg TD I should be seeing somewhere around 15 psi. And it’s running 8psi. Temp is dropping though. Needs a little more diagnostic work....


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Defrost clocks are needed.
1 1/2 - 2 hours off cycle during closed periods.
I prefer LP control for temperature control. Cut in corresponds to 38°F

Remember these are S L O W responding to temperature changes.

Gravity coils are usually huge in size compared to forced air coils.

Purpose is to keep humidity up in the case.
Generally I have seen 15F to 25F TD on most cases with them. Gotta have a higher TD for gravity coils usually

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Display case, gravity coil

Gravity coils are new to me. Just looking for a technical manual or any info on them. I’m curious about the TD, pull down rate, defrost schedule etc.