Milk Vat over controlled

As a virgin user I am straight away asking the assistance of your wise and experianced minds.
I am currently working on an aged milk vatutilizing a kelvinator modrl 72 condensing unit,the problem is it not only runs a TX valve but also a hot gass bypass.
O.K. the hot gass bypass may be for downloading and anti-ice but it in turn is controlled by a pressure controll tapped off the TX pressure equaliser.
I have the system running reasonably well but am still experiancing some frost back to the compressor even though in am running a 8 k superheat.
Does any one have any good ideas on the reasioning for the extensive array of controls and any advice for the liquid return:confused:

Quote:

---

the hot gass bypass may be for downloading and anti-ice but it in turn is controlled by a pressure controll tapped off the TX pressure equaliser.

---

If you mean the TEV and hot gas bypass equalizer lines are connected together to a common equalizer line, which then is connected to the suction line, this is quite ok.

Quote:

---

I have the system running reasonably well but am still experiancing some frost back to the compressor even though in am running a 8 k superheat.

---

Frost alone is not an indicator of floodback, particularly if you are confident of you 8 K superheat reading. But if you are cooling milk, the Prof would think you would be operating at high enough evaporating temperatures such that frost would not form on the suction line, even if you were flooding. Perhaps the evaporator coil design is such that you must operate at a high TD? What is the hot gas bypass valve set at? The hot gas bypass valve may be simply set too low.

Also, milk cooler units in general can have poor evaporator coil designs, allowing refrigerant to trap within the coil during normal operation. The floodback you suspect may be occasional liquid slugs coming from the evaporator.

What are the following:

Low side:

product temp?
SST (saturated suction temp)?
suction line temp (near compressor)?

High side:

cond air in temp?
cond air out temp?
SCT (saturated condensing temp)?
liquid line temp (at receiver)?

Thanks for the help,after your advice on the questionable evapotrator I had a closer and less rushed look at the total design not just the bits I was working on.
I discovered the liquid feed from the TX was split and running two seperate evaporator coils both common feed to a manifold before feeding via a heat exchanger to the suction line.The TX valve sensor bulb was attached to the middle of the manifold and was only sensing one of the coils,fine when everything is balanced I suppose but over the years tube repairs and maybe oil acculimation seem to have cause the coils to become out of balance one flooding while the other is starving and of course the sensor bulb had to be sensing the starved coil didn't it.
By moving the sensing bulb to the other side of the manifold(involving some tricky relocationto find a horizontal section big enough)the system works much better.One side coil may not be up to full efficancy but at least it seems to have the liquid return
Thanks again for tip on where to look
Product temp 2c to 3c
Head pressure 140 to 170 psi
Suction pressure 15 to 25 psi
Hot gas by pass is operated by a pressure control set to open a solinoid at 15psi