expansion valve with MOP

[philjd26]

hi

i am having an intermitting prob with the circuit on a tecnair downflow!!!
every couple of weeks the evaporator ices up restricting flow causing high room tev,when i arrive to site the tev main boby is iced up also.
the external equalise line is frosted a little near the compressor side but nothing towards tev.
i noticed from previous threads that the power head must be warmer than the bulb to prevent mop..

this is a comms room with a 20 degree setpoint!!!

is there a good way to test these, as when a normal tev goes, it goes!!

i am thinking moisture also..

any thoughts ??

rgrds p

[Grizzly]

Hi Phil.
Just out of interest, what make TEV is it you have?
I have seen Danfoss ones where the "O" ring on the orifice cage is passing and causing the External Balance line to freeze up.
When that occurs we normally just change the orifice assy!
Grizzly

[NoNickName]

Sorry, can you please explain once again where is the external equalisation? Surely it shouldn't be where you said it is.

Secondly, can you please inform us about the pressure and temperatures, including superheating and subcooling?

[casstrig]

A TXV valve with Mop means that the bulb instead of being liquid filled contains only a small amount of liquid limiting the amount of force that the diaphragm can exert being used to limit compressor load, so as you have rightly said the liquid can migrate to the diaphragm if it gets too cold causing the valve to close.What I would suggest is that you replace this valve with one without Mop as it is a coms room the load does not have great variations so Mop is not needed.

[philjd26]

Thanks for replies

The make I think is Sporlan griz, also the usual restriction symptom of low back pressure with high super heat and high subcool... This is happening on 4 units so it all common with this batch of units!!!

Equalise line is located at the end of evaporate coil, there is no reason why these systems should go into mop.. Head pressure 19 bar @ liquid 38c... Back pressure as 4 bar with 4 c temp...


Any thoughts??