Unusual Hot gas Defrost Configuration - R22 - comments please

[mr.ice]

I've come across a system which I have been asked to recommission.

A single compressor and evaporator on low temperature, water cooled shell and tube condenser.
The defrost appears to be hot gas. The hot gas is teed off to a gas powered solenoid on the suction. Looped around this valve is a back pressure regulator which I am told is set at +10 degrees Celsius.

There are two accumulators between the evaporator and the compressor, one vertical, the other a horizontal one which has 3kW of electric heating element strapped to it - I imagine to flash the liquid off to try to protect the compressor.

The electrical is a bit of a birds nest and I haven't really figured it out yet. But it looks like there is a solenoid that turns off for the hot gas entering the distributor, so when it comes off defrost, that shuts down, leaving the back pressure valve in circuit for what could be up to 10 minutes if the timer is anything to go by.
Then the hot gas is turned off, collapsing the suction solenoid. It supposedly cleared the evaporator of liquid and allows it to run back down to temperature again with an unrestricted suction.

I've never seen this before, and single compressor/evaporator systems are usually pretty useless without a heat source. I have spoken to a man who is adamant that it used to work, but we've all heard that.

I would be interested if anyone has come across a similar system, or has comments to offer. It just might save me having to pull it all apart to see if it has a chance to work. Thanks.

[mr.ice]

Having trouble finding the right place, so this is a re-posting of a question which didn't achieve a response in the other thread.

I've come across a system which I have been asked to recommission.

A single compressor and evaporator on low temperature, water cooled shell and tube condenser.
The defrost appears to be hot gas. The hot gas is teed off to a gas powered solenoid on the suction. Looped around this valve is a back pressure regulator which I am told is set at +10 degrees Celsius.

There are two accumulators between the evaporator and the compressor, one vertical, the other a horizontal one. This second one has 3kW of electric heating element strapped to it - I imagine to flash the liquid off to try to protect the compressor.

The electrical is a bit of a birds nest and I haven't really figured it out yet. But it looks like there is a solenoid that turns off for the hot gas entering the distributor, so when it comes off defrost, that shuts down, leaving the back pressure valve in circuit for what could be up to 10 minutes if the timer is anything to go by.
Then the hot gas is turned off, collapsing the suction solenoid. It supposedly cleared the evaporator of liquid and allows it to run back down to temperature again with an unrestricted suction.

I've never seen this before, and single compressor/evaporator systems are usually pretty useless without a heat source.
I would be interested if anyone has come across a similar system, or has comments to offer. It just might save me having to pull it all apart to see if it has a chance to work. Thanks.

[RANGER1]

mr ice,
I know you have tried to write a lot of detail, but a system scetch would be good to go with it.

The hot gas does not have to be hot to defrost it, its the pressure & latent heat that do the job.

Is it on an ice machine, or freezer evaporator?

[mad fridgie]

Dito, a picture says a 1000 words

[Royal241]

So what's the problem? Maybe it's late and missed something, check your electrical, all the valves, turn it on. Ohm the compressor, see maybe that's the reason it was shut down, check for ground all around. Wear good rubber shoes when powering this :)

[R. skiffington]

The strange set up may be due to the water cooled condenser. You may already know but for a system with an air cooled condenser in hot gas defrost you simply have solenoid in a line between discharge and entrance to evaporator (after TX valve) just like most ice machines. With a water cooled condenser you'd have to stop water flow during defrost, but even then the water left in the condenser may be enough to suck most of your heat so then you might have to consider stopping discharge flow into the condenser but this creates obvious risks for compressor damage, that may be why the two accumulators have been installed (weird). Going back to what you described as a "back pressure regulator" I assume you mean CPR ( crancase pressure regulator) it would make sense to be using that after the defrost due to the high load but can't imagine why it would be set as high as +10 degrees and You'd think it would stay in circuit the whole time not just for 10 min (that's assuming it is a CPR). The gas powered solenoid you mentioned, do you mean gas assisted, so still has a coil? It's hard to visualize what you're looking at exactly, does it look like it's set up like that in the factory or some bright kiwi fridgi has had one too many bright ideas. And what's the actual problem? Not defrosting?

[RANGER1]

It sound similar to a Vogt ice machine, thats why it would be nice to know if it is that or something else.
They have 2 suction slop pots in a row to eliminate liquid carryover, with liquid line going through them to boil it off.