3 metre display case not working very well

[i hate the cold]

hi all, can anyone help me, i have a 3 metre display case that isnt cooling very well only down to +10 at best on a very hot day. the condensing unit is a danfoss maneurop 2.5hp at a guess two fan condensing unit on r404a.
the problem is the pressures are quite high 55psi back pressure and 300psi head pressue and a red hot liquid line, the sight glass isnt full it is flashing so i added some r404a then the pressures got higher, i thought it was air in the system so i took all the gas out changed the oil, drier, tev the lot, gave it a good long vac, problem still came back plus the condensing unit was moved with 6 extra metres of pipework added, could this be that the condensing unit isnt big enough. please help and thats for reading all of this.
kindest regards.

[expat]

It would be nice to know the temp of the liquid line and where abouts you take that temp. I am presuming that this is a static evap.

Has the display case been modified in some way that is interfering with the cold air convection?

Does the evap have a uniform temp over it's surface?

[marsVesselin]

The condenser surface is dirty. Wash with water jet taking care not to bend the fins. If there are bended fins you should straighten them up. Water from a hose doesn't work you need water jet. Clean well and that is all.

[thebigcheese]

sounds like a dirty condenser ( note it may look clean but be cloughed up) or a smaller condenser fan has been fitted. is the condensing unit out side? and what sort of air temp have u got?

[taz24]

hi all, can anyone help me, i have a 3 metre display case that isnt cooling very well only down to +10 at best on a very hot day. the condensing unit is a danfoss maneurop 2.5hp at a guess two fan condensing unit on r404a.
the problem is the pressures are quite high 55psi back pressure and 300psi head pressue and a red hot liquid line, the sight glass isnt full it is flashing so i added some r404a then the pressures got higher, i thought it was air in the system so i took all the gas out changed the oil, drier, tev the lot, gave it a good long vac, problem still came back plus the condensing unit was moved with 6 extra metres of pipework added, could this be that the condensing unit isnt big enough. please help and thats for reading all of this.
kindest regards.


Maneurop compressors are good compressors as a rule. It sounds like your condenser was a bit blocked and the system was not condensing correctly.
That would put bubbles in the liquid line. You then have added extra refrigerant and took the head preasure up even higher.

You will need to clean the condenser then recover the refrigerant charge and correctly recharge the right weight of liquid into the system (refrigerant weight will be on the label).

Just so you know you must never just top up a system that seems short of refrigerant. You must always find where the gas has gone and add new refrigerant to the system.

taz.

[FEISTY]

First I would watch that " weigh in the charge " idea. TXV system should mean receiver and you said pipe was added to run. That would alter any factory capacity spec on label. Pressures, operating temps and subcooling / superheat will be the only correct way to set-up system. Good luck and take your time. FEISTY

[i hate the cold]

hi and thanks for replying, the condenser is clean with original condenser motors, the sight glass when i found had flashing through it and felt the liquid line was red hot about 46 degrees c, so i first thought the system was undercharged but noticed the high head pressure so i thought there was air in the system so i recovered all the refrigerant, changed the oil in the pot, the drier and the TEV, and put on a 24hr pressure test which held. do you think i should tell the customer he needs a bigger condensing unit.

[thebigcheese]

i think u should just change it sure uve changed everything else ( only joking)

can i ask why u thought it was undercharged if the liquid line was realy hot?

[icecube51]

how about the TEV, did you took a look at the orifice and filter ??? did you look if the orifice maths the new set-up ??.
i remember to moved a 7mtr cabinet ,3mtr+a curve of 2mtr + 2mtr,and changed the combination.where before the 3mtr was i put in the 2mtr. also the goods where changed.took me 2 days to figure out to change the original orifice,and get it straight.
where is the magnet valve , to the cabinet or close to the comp unit?? is the thermostat for the hole cabinet, or is there more than one ?? how is the sensor placed??

and, don't hate but love cooling,you work better,you see.:)

Ice

[a/c.king]

look my friend take it easy and dont complecate the problem.on hight pressure 300psi and 55psi low pressur there is four simple faults.
1.condenser its durty
2.txv orofice dont suite ur unit
3. low compressor pressur because of faulty pressur holding valve insaide the compressor
4.condensor unit dont duite evaporater or heat load required.
king

[Peter_1]

high 55psi back pressure and 300psi head pressue ..red hot liquid line, the sight glass isnt full it is flashing so i added some r404a then the pressures got higher, i thought it was air in the system so i took all the gas out changed the oil, drier, tev the lot, gave it a good long vac,

Some thoughts:
why you changed oil, TXV, drier...they all haven't anything to do with our problem
There's difference in flashing gas or not enough refrigerant.
What did you decide you added some gas?
Why you think HP raised when you added gas?
Air in the system...if you take the right measurements and make the right conclusions, then you no longer have to guess but can conclude for sure.
A long vacuum procedure is not always a good vac.
You don't need a long vac but a sufficient low vac.

[multisync]

Dairy decks need 1.5 - 2 kw per metre.Start there and come back..

Multisync
London

[maverick]

I found on the Maneurop , the front may look clean but inside the coil will be dirty, if you can wash with condenser cleaner and water and make sure the right condenser fan motors are fitted to it.

[fridge doctor]

Apart from the flashing gas, and in this respect I go along with others on dirty condenser/inadequate airflow. What about the case itself. Does it have covers, if not is air from a fan or Ac unit interrupting the normal cabinet air flow cycle. It isn't clear whether you are referring to a dairy multi deck or a serveover ? If a multi deck Is the product overstacked forcing return air out of the cabinet. Try the cardboard test. Get some flattened boxes, tape them together and fit a temporary cover on the case, if 'lost air' is the problem you will see a rapid drop to the correct temperature in minutes.

Trevor

[MOHAMMED ASHRAF]

1)assure that condunsation is very well..2)also display unit markets are need good air conditioning.approx below 28 deg c.3)check oriface.

[Gary]

Check the temperatures of the air entering and leaving the condenser. The difference between these two temperatures is the condenser delta-T (dT). The condenser dT tells you if you have sufficient airflow. More than 30F/17K dT indicates insufficient airflow.