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The system was frozen over so I defrosted it cleaned the coils inside and out changed the filter, the unit will still not cool, so I attached my gauges and checked pressure cross referenced with my slide rule and found it to be a little low, after charging the system to a point that it would cool properly the high side would bounce from 450psig to almost 600psig and then cut out, why would it be bouncing? I thout it might be an over charge so I recovered the refrigerant that I put in and started over and it did it again, please help i am extremely frustrated.
 

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The system was frozen over so I defrosted it cleaned the coils inside and out changed the filter, the unit will still not cool, so I attached my gauges and checked pressure cross referenced with my slide rule and found it to be a little low, after charging the system to a point that it would cool properly the high side would bounce from 450psig to almost 600psig and then cut out, why would it be bouncing? I thout it might be an over charge so I recovered the refrigerant that I put in and started over and it did it again, please help i am extremely frustrated.
What are the other numbers...? suction pressure, superheat, subcooling?
 

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Contaminants in system. Recover, repair leak, replace FD, pull proper vacuum and recharge.
 

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What are the other numbers...? suction pressure, superheat, subcooling?
You never came back and answered the question. :001_unsure:

Did the head pressure actually "bounce" or just go from 450 to high pressure limit trip?

The fact additional charge got the system to "cool properly" (load the evaporator coil) would suggest the TXV isn't opening enough or there's a restriction. The additional head pressure forces more liquid through the valve or restriction.

Faulty TXV's will sometimes initially react favorably to the additional head pressure but close back down after a while. Or if the airflow is still low, the valve would adjust and close down. The only remaining possibility is a liquid line restriction.

I'm still guessing the high head is due to overcharge. I'm would also bet the subcooling is way high, if you calculated it.

If the superheat is somewhere near "normal" the problem is low air. If the superheat is high, the problem is the TXV or a restriction. If you take a few temp measurements, the cause of the problem will become more apparent. ;)
 

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You might have moister in the system? I had a unit last year with simular problems... I reclaimed the refrigerant, and pulled a vacuum, recharged the system, and it seemed to do the trick... It was a last resort though, I tested everything else first
 

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450 seem kinda high fluctuating 200 lbs. is NG.
It the pressure is jumping fast from 400 to 600 you may have air/moisture in the system and I would do what Archie recommended.

How did you clean the condenser coil? Did you use chemical to clean deep in the fins?
 

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Trane 410a issues

Your issue sounds like a FD plugged. We have had new York 410a RTU's with this same thing happening.
Many of these new units are made/assembled in Mexico or other countries with lower pay scales/skills. Don't sneeze, there goes another American's job!:furious:
 
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