need some answers plaease

[sean1]

hi all hope some of you can help.
i have a beer master unit that wont pull temp below 16celcius. the suction pressure is 2.5 barg running on r134
the unit has condensation on the compressor covering about 80% of it-only the top has'nt. also the liquid line is warm to touch right up until the expansion valve - is this normal? is it possible the expansion valve is stuck open? if so how would i check
thanks in advance

[sean1]

sorry forgot to add the condensing unit was changed 4 months ago because of the same problems

[Brian_UK]

and the other readings to help in our diagnosis are ??

[fowlie]

what type of expansion valve is fitted to this unit if its a danfoss tev it has a screw in adjustment.by turning it in clockwise would close the valve and anti the oppisite.
does sound like the valve is flooding back to your comp but could be incorrect sizing of orifice or under sized unit.Is this a case or a coldroom and did the problem start straight after the new unit was fitted or a while later and has any other works been done on this system.

[sean1]

sorry i know there not alot of info. goin back to site monday just wondered what your thoughts would be.what other info would u need and is it possible the expansion valve can do this?

[sean1]

it is a danfoss valve.a tex2 i think or a tx2 with a number 4 orifice the problem has been there for nearly a year. another engineer worked on the unit and determined that it was the condensing unit at fault and changed it 4 months ago. my problem is that every 2-3 months we get a callback for the same problem/same symtoms. i have just recently got involved although i did tell them at the time i was"nt sure it was the condensing unit from what i was told.customer says unit ran ok when unit was changed until recently and no other work was done on it since that till now.is it possible te valve stuck open ? if so how would you check?
thanks in advance any help much appreciated

[sean1]

sorry i know it alot of questions. but what can cause the compressor to have condensation build up on it? is it normal for the liquid line to be still warm just before the expansion valve? just seeking more knowledge and experience

[fowlie]

first thing is to make sure condensor is clean but being 4 months old wouldnt expect it to be dirty much,second if it has a sight glass on the liquid line is it bubbling or clear and does it have a moisture indicator fitted.if showing moisture in systm change drier and fit a new valve+orifice but try and find out if its the correct rating as a tex is for r22 not r134a and a size four is quite big but as i dont know the size of the load it might be correct.hope this is some help

[sean1]

fowlie thanks for the reply. yes condenser is clean and fans working fine[as you said not that old]sight glass is fitted[as standard i think]it is clear but it a light purple coluor which says caution on the outside of the glass. i planned on vaccing and re-charging unit on monday. do u think i should also change expansion valve and drier? brian ur input would be much appreciated-would i be better gettin more temps/pressures before going forward?
sorry fowlie just re-read your message will check valve size etc monday when on site climate centre only 5 min up road hopefully get sorted in one day!

[frank]

Was the old condensing unit operating on R134a?

What gas is the TEV rated for?

[Temprite]

it is a danfoss valve.a tex2 i think or a tx2 with a number 4 orifice

What's a beer master unit?

No 4 orifice is pretty big for commercial sounds like it may be too big. (depends on application)

[tonyelian]

hi
i think there is a problem in the expansion valve orifice .it seem that it feeds too much refrigerant to the evaporator.orifice must match the capacity of cndensing unit @the desired evaporation temp.ther is some thing wrong here txv for 134 is tn or ten not tx so check it

[Peter_1]

What's a beer master unit?

No 4 orifice is pretty big for commercial sounds like it may be too big. (depends on application)

Temprite, I was thinking the same.
What's the type and brand of the condensing unit?
Wrong gas as Frank suggested is of course also possible.

[frank]

We discussed Beermaster coolers here

http://www.refrigeration-engineer.co...ad.php?t=10788

[sean1]

ok went back to site today.after speaking to the technical bloke in the suppliers heres what i did.
1. fit new filter drier
2.fit new valve and orifice no:3

also spoke to the original engineer who wasnt sure if he charged unit with134a or 407c-as supplied and confirmed with technical bloke at the suppliers-who got a bit grumpy i think
ran unit and here is what i got

unit:beermaster bmo150-1
refrigerant:r407c
room temp at time:+17 celcius-evap display
suction:4.4 barg/62 psi
discharge:14 barg/200 psi
suction line temp by expansion bulb:+12 celcius
liquid line @expansion valve:+23 celcius
liquid line into condenser:+56 celcius
liquid line leaving condenser:+31celcius
air on evap:+18 celcius
air off: +12 celcuis
cond air on:+18 celcuis-my thermometer
air off:+29 celcuis
i work this as givin me a superheat of 6 celcius and it seems to pull temp -at15 when left .no condensation on compressor.going to return on thursday and see how it running.what do all of you think of the above?i know it a bit long but thanks again.

[Gary]

It appears to need a little more refrigerant. Is the sight glass clear?

[sean1]

yes but was getting dark when i left site will check again on thursday.but how did you come to that conclusion?- just curious does all else seem ok.are these typical ie should this be what i should be expecting and checking-roughly

[nike123]

liquid line @expansion valve:+23 celcius

liquid line leaving condenser:+31celcius

You still have big drop of liquid line temperature (8K) from condenser to TXV.
Describe what is at that line and its length (together with elbows valves etc...) and insulation and temperatures at pipe location.

[Gary]

I'm thinking that liquid line temp was actually taken at the drip leg. It should have been measured at the outlet of the receiver.

[nike123]

I'm thinking that liquid line temp was actually taken at the drip leg. It should have been measured at the outlet of the receiver.

What is drip leg?

[Gary]

What is drip leg?

The drip leg is the pipe between the condenser outlet and the receiver inlet.

If the sight glass is clear, then the subcooling at the receiver outlet is probably pretty close to the subcooling at the TXV inlet... and the refrigerant charge is probably sufficient.

[nike123]

The drip leg is the pipe between the condenser outlet and the receiver inlet.

If the sight glass is clear, then the subcooling at the receiver outlet is probably pretty close to the subcooling at the TXV inlet... and the refrigerant charge is probably sufficient.

Ok, but what would be cause of cca 8K temperature drop from condenser outlet to receiver inlet.

[sean1]

reading was taken between condenser outlet and receiver

[Gary]

reading was taken between condenser outlet and receiver

The reading should be taken in the liquid line after the receiver... which is probably where the sight glass is.

On systems which have no receiver, the bottom of the condenser serves that function... so on such a system we would take the reading at the outlet of the condenser.

[sean1]

thanks gary will check tommorrow

[Gary]

Ok, but what would be cause of cca 8K temperature drop from condenser outlet to receiver inlet.

There can be some condensing going on in the drip line, especially at the condenser end... so we can't trust that measurement. Also, we don't know if the TXV end of the liquid line is in the refrigerated space or not. If it is, it's temp could be considerably lower.

So... we don't really know if that 8K difference exists.

And the fact that the sight glass is clear indicates that it has sufficient subcooling at that point, which means the temp at the receiver outlet/sight glass must be pretty close to the temp at the TXV.

[nike123]

There can be some condensing going on in the drip line, especially at the condenser end... so we can't trust that measurement.

Ok, thanks for clarification.
When you say that is some condensing going on in drip line, what is cause of that condensation except of ambient temperature (if any other)?

[sean1]

txv is in refrigerated space. will check all u ave said and post results.once again thanks to everyone