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I recently changed out a R-22 system with a 410a system. (Coil and Condenser) I left the original lineset, but flushed and pumped down to 180 microns. The condenser is a Bryant 13 SEER and the Coil is a Horizontal Bryant coil, which is has a TXV and is approx 2 feet below the condenser. I cannot get the Subcooling dialed in, as the head pressure fluctuates between 280 and 410. I thought maybe there were uncondensables, so I recovered refrigerant, pumped down and recharged with fresh 410a. The head pressure still fluctuates, but the compressor does sound better. I'm at a bit of a loss. I'm thinking maybe undersized suction line, or bad txv. Any thoughts?
 

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I would say you have non cond.still in unit possibly a leak.Purge with nitrogen pressure test evacuate change filter drier and charge.Let me know how it goes please.
 

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I'm having the same problem an existing R-22 unit and new condensing unit that takes 407C.
Purged with nitrogen, flushed and sucked it into a deep vacuum. Head pressure going from 170 to 350 and back again. Nutty situation. Gotta be non condensables but can't understand how.
Good luck with that


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I recently changed out a R-22 system with a 410a system. (Coil and Condenser) I left the original lineset, but flushed and pumped down to 180 microns. The condenser is a Bryant 13 SEER and the Coil is a Horizontal Bryant coil, which is has a TXV and is approx 2 feet below the condenser. I cannot get the Subcooling dialed in, as the head pressure fluctuates between 280 and 410. I thought maybe there were uncondensables, so I recovered refrigerant, pumped down and recharged with fresh 410a. The head pressure still fluctuates, but the compressor does sound better. I'm at a bit of a loss. I'm thinking maybe undersized suction line, or bad txv. Any thoughts?


Just wondering why you went with 410A rather than a more R-22 compatible refrigerant line 407C.
Pressures using 410A are huge compared to R-22
Sorry. Just noticed you replaced both coils. My bad.

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