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.
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.