Hi All,

I am having a few problem with a brand new freezer room not working properly. There is a bit of a story to this so bear with me. The freezer coil was originally install on a job a about six months ago, I didn't commission it but after two week of operation and the client stocking the room it wouldn't drop past -12C. After many trips by numerous techs and replacing TEV, upsizing orifice etc. it still didn't work. I was sent to replace the evaporator on this job, I could see by the way that the bottom of the coil was iced the top clear that the refrigerant was feeding properly. It was decided to replace the evap with a model of the same capacity from a different manufacturer. I put it in and it work perfect the room pulled down quickly, all was good.

The offending evaporator was sent back to the manufacturer for warranty. Warranty was denied the said that there was nothing wrong with it, that all pass were correct and it was distributing evenly. We requested that the distributor was replaced which was done before we got it back. So having a brand new second hand evaporator sitting there that has nothing 'wrong with it', it was decided that it would be put it at the next job that calls for a evap of its size.

So it's in at a brand new job, commissioning today job to open on Friday and what do you know this coil is doing exactly what it was doing at the last job. The room is taking forever to come down to temperature. A new room empty from start up to -18C will take three hours max. After 3 it was only down to -8C. The TEV is hunting all over the place I played around adjusting super heat to no avail. I can see the problem the refrigerant isn't being distributed properly. The vapour and the liquid are separating, the bottom of the coil is flooded with liquid the top is getting mainly vapour. This is why the TEV is hunting all over the place because TEV senses the bottom circuit flooded with liquid refrigerant, 0K of superheat, and forces the TEV to close. This causes the top circuits already starved of refrigerant to operate at an even higher superheat. Once the bottom circuit is no longer flooding with liquid, the TEV senses the high superheat from the upper circuits and it open quickly, only to once again flood the bottom circuit and start the cycle all over again.

I am familiar with nozzle type distributors and this manufacturer use to use them they worked fine provided you selected the right orifice. But they have moved to a venturi type distributor, does anyone have any information about this type of distributor? How does it work?

I think there is a fault with their distributor, and I've got the manufacturer coming out tomorrow to show them. But I'm worried if they do replace the coil with a new one under warranty I'll have the same problem. Any thoughts or help would be appreciated.