charliegolf720
04-24-2005, 10:31 AM
Working on a Trane 6 ton A/C unit which runs year round to cool radio transmittor equipment. The orginal complaint was that the transmittor equipment were reaching high temperature levels, close to trip out.
When I got there, the t-stat was oviously calling but the compressor would not run. I traced the lock out to compressor OLs, which were open. I opened the disconnect and allowed the compressor to cool down. After a coffee run, I ohmed the OLs. They were now closed so I put power back to the unit, it immediately started up. Both suction and liquid line pressures were 120 psi. After about four and a half minutes of no pumping, the windings heated up enough again and the thermal OLs opened. I determined that either the suction and/or dicharge valves in the hermetic unit were damaged. The compressor would have to be replaced. Just to sure, I allowed the unit to cool down once again and went through the entire system. All valves in the circuit were open for refrigerant flow. The second test had the same result as the first.
The following day, I replaced the compressor (Trane GP813-NN3-G), suction filter, and liquid line drier. The name plate refigerant charge for the condensing unit was 13 pounds of R-22 plus with line sets, estimated another pound to start. The unit has a 5 ton nominal TXV. So I decided any additional charge, if needed, would be measured in using the subcooling method (15 degrees).
Well, I started the unit up and immediately things wern't right. Suction 30 to 20 psi. Liquid line pressure decreased to between 75 to 55 psi. The liquid line frosted right up. The unit would cycle on and off on low pressure. The charge was weighed in. Could I be that low on charge? If anything, the liquid line was so cold, you would think I way over charged it.
Anyway, when it cycled on and ran, I noticed a slight hissing sound coming from the unit. That seemed to explain my problem. Somewhere, there was a restriction to flow in the system. I shut the unit down and again checked valve positions, everything lined up.
Looking at the frosted liquid line, I spoted something I neglected to notice, a small factory installed drier. Great, I thought, I found the problem. I recovered the charge and removed the resricted drier. I ran 3/8" OD tubing in its place since I already had a new drier installed down the line. Dehydrated unit and put the charge back in. Problem solved right?
Nope. Started up unit and again had low suction and liquid line pressures. Again, liquid line was frosting up. Hissing sound was back. This time I could hear it better. It seemed to come from the suction line accumulator. This must have been the original obstruction.
Anyway, the customer is already crying about cost of repairs, the ussual. My question is, can I remove the accumulator all together? There seems to be a good year round heat load. I see why it is there, but do I really need it? Please offer some sound advice. Tension tight and this job is starting to make me look bad. Any help would greatly be appreciated.
Make: Trane
Model: TTA072C300A0
Charlie
When I got there, the t-stat was oviously calling but the compressor would not run. I traced the lock out to compressor OLs, which were open. I opened the disconnect and allowed the compressor to cool down. After a coffee run, I ohmed the OLs. They were now closed so I put power back to the unit, it immediately started up. Both suction and liquid line pressures were 120 psi. After about four and a half minutes of no pumping, the windings heated up enough again and the thermal OLs opened. I determined that either the suction and/or dicharge valves in the hermetic unit were damaged. The compressor would have to be replaced. Just to sure, I allowed the unit to cool down once again and went through the entire system. All valves in the circuit were open for refrigerant flow. The second test had the same result as the first.
The following day, I replaced the compressor (Trane GP813-NN3-G), suction filter, and liquid line drier. The name plate refigerant charge for the condensing unit was 13 pounds of R-22 plus with line sets, estimated another pound to start. The unit has a 5 ton nominal TXV. So I decided any additional charge, if needed, would be measured in using the subcooling method (15 degrees).
Well, I started the unit up and immediately things wern't right. Suction 30 to 20 psi. Liquid line pressure decreased to between 75 to 55 psi. The liquid line frosted right up. The unit would cycle on and off on low pressure. The charge was weighed in. Could I be that low on charge? If anything, the liquid line was so cold, you would think I way over charged it.
Anyway, when it cycled on and ran, I noticed a slight hissing sound coming from the unit. That seemed to explain my problem. Somewhere, there was a restriction to flow in the system. I shut the unit down and again checked valve positions, everything lined up.
Looking at the frosted liquid line, I spoted something I neglected to notice, a small factory installed drier. Great, I thought, I found the problem. I recovered the charge and removed the resricted drier. I ran 3/8" OD tubing in its place since I already had a new drier installed down the line. Dehydrated unit and put the charge back in. Problem solved right?
Nope. Started up unit and again had low suction and liquid line pressures. Again, liquid line was frosting up. Hissing sound was back. This time I could hear it better. It seemed to come from the suction line accumulator. This must have been the original obstruction.
Anyway, the customer is already crying about cost of repairs, the ussual. My question is, can I remove the accumulator all together? There seems to be a good year round heat load. I see why it is there, but do I really need it? Please offer some sound advice. Tension tight and this job is starting to make me look bad. Any help would greatly be appreciated.
Make: Trane
Model: TTA072C300A0
Charlie