Disappearing superheat?

[craig1]

I have a market with Hussman Protocol "mini-rack" system that I've been taking care of for the past year. It was installed in '03 and all their old cases were connected to it. At the same time a 10 door ZeroZone reach in was installed. Over the time I've been servicing the store I've watched as the suction stop valve to the ZeroZone became increasingly incased in ice and the suction filter grew into a watermellon sized ball of ice. I suspected a problem, but kept brushing it off as excessive humidity in the basement and no ventilation. The compressors always had plenty of superheat so I didn't really worry about it.

Today I stopped by to pick up some groceries and the owner showed asked me to look at the system. He had opened the door on the protocol and the lead compressor was completely encased in ice and the second compressor partially covered. I found the sight glass flashing and the receiver at 0%.

Since I had previously suspected problems with the zerozone I checked there first. I had to turn both TXVs on the system in 3 turns to get 5 degrees evaporator superheat. after I did this, the ice started melting on the compressor and the receiver level went up to 10% as all the liquid was pulled out of the suction header.

I would normally suspect that the TXV's were never set, or set improperly after installation, but from what I saw happen it seems like the TXV's lost superheat over the course of the year? is that possible? They're Sporlan valves and they are properly installed. I know for sure that no one besides me touched this system over the course of the year.

[thefreezerguy]

Are they standard or balanced port?
Has there been a dramatic change in head pressure (floating head) or liquid subcooling? Are the cases equipped with distributors? If so, are they correct for the gas being used?

[jpsmith1cm]

Loose bulbs?

Ice ups, bad fans, loose/missing/backwards blades? In other words, airflow problems?

It is conceivable that debris could get stuck in a valve in such a manner to keep it from closing.

[craig1]

Are they standard or balanced port?
Has there been a dramatic change in head pressure (floating head) or liquid subcooling? Are the cases equipped with distributors? If so, are they correct for the gas being used?


valves are balanced port, head pressure is fixed at 212, no changes that would effect subcooling. The cases do have distributors. I did not look at them. The system uses R-404 and the TXVs are R-404 rated so i have no reason to believe the distributors are wrongs, but you never know.

[craig1]

Loose bulbs?

Ice ups, bad fans, loose/missing/backwards blades? In other words, airflow problems?

It is conceivable that debris could get stuck in a valve in such a manner to keep it from closing.

bulbs were tight and installed correctly. I did find one fan out of 10 that was not working but started when I gave it a push. I replaced it.

[Phase Loss]

I had to turn both TXVs on the system in 3 turns to get 5 degrees evaporator superheat.

Now we know the superheat is 5*

BUT

we don't know what the superheat was a year ago. no one checked it right? hard to say they lost their superheat setting when there is nothing to compare the current value to.

If the SST and SCT did not change. Best you can do is monitor over time.

[craig1]

Now we know the superheat is 5*

BUT

we don't know what the superheat was a year ago. no one checked it right? hard to say they lost their superheat setting when there is nothing to compare the current value to.

If the SST and SCT did not change. Best you can do is monitor over time.

I don't know what the evaporator superheat was previously, but I know the many times I've been there for various things in the past, there was always compressor superheat. Now there was none. and it seemed like none by a far margin judging by how much liquid was returned to the receiver once I got it set up right.

[frigeguy]

Basic 101 ..seems you would be correct ( adjusted superheat ) I start up zero zone and a number of other manufactures daily you did the right thing. Do not assume the superheat was set correctly at install. I have seen 3 ft balls of ice after systems have run incorrectly for years. No one seems to notice and i'm guessing the hot water hose was out quite a few times over the course of time.