urgent

[Dimitris]

I have a Rack with 2 Bitzer compressors, 2 stage Model S6F30. The tunnels are -35 celcius. I replaced one of the compressors because the second stage valves (discharge valves) were broken. I noticed that the rear part of the new compressor, after the second stage suction, freezes. I closed the TXV of the sub-cooling one notch. The problem was solved, but after 2 hours of working properly, the same problem appeared. I closed the valve one more turn and the problem again fixed temporarily for about 2 hours. After the second time, I closed the TXV completely. The freezing problem disappeared again. I am now waiting to see the results in the morning. Superheat is 20 degrees celcius.
I would appreciate any feedback. It is 10:00 pm and I will be going on site again in the morning. Thanks. Dimitri.

[The Saint]

Your valve doesn't feed enough. You should check the following:
Shortage of refrigerant
High Superheat
Flash gas in line
Faulty or dirty expansion valve
Incorrect size of TXV
Incorrect location of bulb

[US Iceman]

Dimitri,

If the evaporating temperature is -35C and you have 20 degrees of superheat, the actual return gas temperature to the compressor is still -15C (5F). At that temperature the suction gas is still below the freezing temperature of water.

Frost on a compressor housing does not mean liquid is present in the suction gas!

[NoNickName]

I was in the process of answering, but Iceman was faster.
With any setup, the suction of that compressor will be frozen. I don't see how it should not freeze, unless superheating will be more than 35°K, which is not a good idea.
Let it freeze and rest in peace.

[BESC5240]

As I understand it the freezing does not occure on the the suction side of the compressor, but on the intermediate stage.
What is the pressure you have in the crank case ( = intermediate pressure) ?
What is the superheat at the 'rear part of the compressor' (= second stage inlet) ?

[chillin out]

I was in the process of answering, but Iceman was faster.

@NoNickName, this thread has been up for 4 months now...lol

A snail walking around the world would be faster.

Hehehe

Chillin

[NoNickName]

We gave you a chance of answering, chillingout, but in the last 4 months either you were too busy, or didn't care.

The Saint brought the thread up and Iceman and myself didn't have a look at the posting date. It may help somebody else.

[Gozzy]

Hey your valve is pouched, or your buld is in the wrong spot. What's your sub cooling at ? When's the last time you did a full PM ? What concerns me is that you have that TXV at full close (that's not good good)