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iceman007
14-06-2004, 08:28 PM
Went today to one of these units. Temperature inside the case is 15 degrees C. All the condensing unit and twin compressors underneath. Checked the cabinet, and as I was expecting it's warmer on one side and cooler on the other.
Someone previously had installed 2 line tap valves, one in each suction line-saved me the bother.
One compressor head temp is 55 degrees, the other 105 degrees, so straight away I thought there would be no gas. Took the pressures and the circuit with the higher temperatures on the compressor and discharge line has a suction pressure of 80 psi-it's on R404A by the way-gives an evaporating temp of 2 degrees-I would have expected -10 for this type of application. The other circuit suction is 40 psi-evaporating at -14 about right. During the defrost cycle, the case temp actually started to fall-evap fans are supposed to run on these units during defrost. In the condenser the inlet pipe temp is 65 and 55 degrees and outlet before the capillary is 27 and 26 degrees!!. But the delta T for the condenser airflow is only 4 degrees- on at 23 and off at 27. Anyway, I connected the gauges to the circuit which I had identified was a problem, and the standing pressure during the defrost is 95psi-which I had expected to be a bit higher in a 23 degree atmosphere. When the compressors start back up, theres hardly any pulldown and the suction pressure after 20 minutes is still 90psi-only dropping by a few psi, and way too high, both suction lines are at around 20 degrees, giving a massive superheat. Listened to the compressor and picked up an odd noise, like hissing gas. I thought that the suction valves were to blame, but there are no service valves so I can't try and pull a vac with the compressor, but think that the heat is being generated because this compressor is running but not pumping properly, so no condensing etc.
Anyone have any other ideas??

Regards
James

PS Apologies for the length of this thread.

mrchatts
14-06-2004, 08:41 PM
this compressor is running but not pumping properly, so no condensing etc.
Anyone have any other ideas??

Sounds about right to me.......try stopping your evap fans and see if the suction pressure drops.

iceman007
14-06-2004, 08:52 PM
That was quick Mrchatts

It was the most obvious one to me-also explains why one side is warm and the other colder- 2 evaporator coils I think. Looks like another compressor change!!

Best Wishes
James

mrchatts
14-06-2004, 09:06 PM
It was the most obvious one to me-also explains why one side is warm and the other colder- 2 evaporator coils I think

Iím not sure if there are two coils side by side, I would say the coils runs full length of the case and is shared by both units, one thing to check is that no Air con is blowing into the warm side Oh! and of course a super clean condenser is a must, not that you havenít checked that already.

iceman007
14-06-2004, 09:16 PM
mrchatts you are probably right about the evaporator, the condenser has a similar set up, it's shared by both fridge circuits, one has the top half and the other has the bottom half, it's totally clean-funny enough the first job I had today was a dirty condenser-R22 85psi suction etc etc. Oh- and theres no a/c blowing on there.

Many Thanks
James

mrchatts
14-06-2004, 09:25 PM
Have fun changing the compressor James, bet you canít count how many you've changed this month :(

iceman007
14-06-2004, 09:37 PM
This will be my third in two weeks, plus I have another two air con ones to do-still I'm not complaining keeps me in a job.
Funnily enough I've had loads of problems with these dairy cabinets, as I took a contract on for a supermarket, and the prevoius maintenance is hardly existent. They're paying now for the previous cutbacks-Being Pennywise and Pound Foolish I think is the expression

James

Latte
14-06-2004, 09:42 PM
Hi Iceman,
Comps are not too difficult to change on these have done plenty. Check he conderser fans, should be 10w but 7w ones are commonly incorrectly fitted because these were always easier to get hold of. Be very carefull as you pull the unit out as the driers and the cap tube are normally located behind the LH front leg and can easilly be kinked.
Quick piece of advice if anyone ever gets called to one of these and only one comp works. The staging for the second compressor goes through a light tube fsu started in the electrics box to stop it coming on at the same time as the first (Quality !!!!!!! :eek: ).

These units do suffer badly from blocked condensers & condenser fan problems.

Regards

Raymond

iceman007
14-06-2004, 10:12 PM
Hi Raymond

I noticed the cap tubes and driers all squeezed in behind the left leg-both compressors running, just that one of them isn't doing the job properly. Not a difficult job to change it anyway. Should do the trick.

James