DENCO problems?

[Lobozoo]

:mad: So i have been working on a couple denco units in a film storage room , the dencos run on R134a and due to the nature of the room and whats in it , the units have also been fitted with a hot gas bypass to make sure the humididty stays low.

We have just finished the first, it had lost all its gas due to a few leaks in the system, but thats all sorted. I i recharged the the first unit to the sight glass and ended up adding 3.1kg of gas, unit works perfect clear sight glass and cooling nicely.

So we then moved on to the next unit wich was running but the sight glass was stuck at half and not clearing, i assumed another leak right? ...... wrong!!!
I i actually ended up recovering 4.6kg of gas out of this system even though the pipe leanghts for both units are the same +/- 1m or so.
Tested the system no leaks.

So my question is..... what could be coasing the sight glass to flash? The only thing i can think of is the dryer and as we speak we are changing that so it might fix it or not, just wanted to see if anyone had any other ideas .......?

thanx

[Denco Technical]

Hmmmm interesting, did the drier have any temp differance?


Does the glass become clear, only to resume bubbling later?
Then after a few minutes, clear again?
Repeating this pattern over and over?

Here's a few suggestions.

The pattern could be the result of the expansion valve metering the refrigerant into the evaporator.
As the valve opens it increases the flow, out of the liquid line, causing the glass to flash.
When the valve closes, the flow is restricted and the refrigerant "backs-up" in the liquid line. The glass becomes clear.

Normally this should not happen, if the refrigerant lines are properly sized and installed.
Is the system hot gassing all the time?





what pressure does the hot gas valve open up?

[Gideon Beddows]

the sightglass should really be ignored, chap.
My advice to you is to wind the hot-gas bypass valve out so that it does not hot gas at all and then charge the system so that you have the correct subcooling. You should be looking for about 6-9 K? Then set the hot gas bypass valve to operate at about 1C or higher if you are worried about over cooling.
Cant really help you with the pressures as i have no comparitor on me!! I dont commission that many R134a units. If it was R407C, i'd know them off by heart - cos im sad that way