fluctuating liquid pressure

breeze

replaced a R22 residential split with a  R410 split system, 3 ton.  used existing line set, 15 feet, condenser 2 feet above evap' coil, no old joints, flushed line.  On start-up liquid line pressure fluctuated consistently from 280 to 480 psi.  Piston type metering device on Goodman equipment.  rain downpour prevented me from further diagnostics and figure I must have some restriction in liquid line but puzzled due to thorough flush and evacuation. Only Goodman equipment seems to throw me curves.  Piece of brazing/solder in line is the something that might cause this sympton, but the fluctuation is curious.  Maybe others have had start-up problems with these 13.0 SEER condensers.

Ironman

fluctuating liquid pressure

Did you thoroughly purge the flush chemicals out with nitrogen and then pull a vacuum to 200 microns? New coil or old? If old, you may have residual mineral oil.



The 13 seer Goodmans have 1/4 in. tubing in their condenser coils and can not tolerate any non-condensibles. You also cannot pump down the system charge into the condenser like you could with the old 3/8 coils.  The charge on these new ones is critical.



If you're OK on the above questions, then there may be some debri or the piston may not be seating correctly. Is the piston the size called for with the O.D. unit? Remember, the I.D. coil does not determine the piston size, the O.D. unit does. Is there any flashing in the liquid line? If so, consider one of the above causes.

breeze

fluctuating pressure

New coil, I flushed and purged and triple evacuated.  I did change the the piston and you may be right about not seating or I got something in the line that is preventing the piston from seating.  Thanks for the info, I did not know about the 1/4" tubing.  I will reclaim and check the piston, and basically redo. 

Paul Fredricks_3

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Be sure to weigh in the charge to be accurate.



A restriction in the liquid line will not cause high head pressure. Insufficient condenser air flow or non condensables are usually the reason for high head pressures. Unless it's really hot out I wouldn't think your head should get near 480. But I think it can't hurt to check that piston, then re-evacuate and charge. Odd one.

Techman

Head Press

Is that a two speed cond fan motor?

breeze

head pressure

no.  single speed 13.0 SEER.  I doubt it is condensibles; must be a something clogging the metering device. 

Techman

Low side press,

What was it while the hi side was varying? Superheat/subcooling?

Empire_2

Back up a little?

Let's reclaim 1/3 of your charge,.....  You are overcharged!!!  I'll bet that when your head rises to 480psig, you suction takes a dip...?  Am I right?  As the suction pressure goes down, the liquid being jammed into the restrictor has  more room to basically move into the lo side, and thus suction comes up, head goes down,...AND repeates.  Your restriction is the refrigerant itself.  Accurators work on poressure diff.  only, period.  Save time and just get rid of your excess charge.  This is only my opinion and I hope I'm not steping on any teos here.



Mike T.

breeze

fluctuating pressure

Suction pressure didn't budge.  120psi    Remember, new unit, factory charged for 15' line set, I have a 17-18'. I only let it run for 5 min due to rain and haven't been back, rain hasn't stopped for a month here in western PA., so I haven't taken any sub-cooling or superheat numbers.  I'm thinking its  some restriction but the consistancy that the guage moved 200 psi up and down was perplexing.  If the piston was blocked head should rise and suction drop.  I've run into beads of solder in systems that would block the piston sometimes and not others but the pressures reacted accordingly.  Makes me question my condensing unit.  the first step I plan on taking when I return to the system is to isolate the condensing unit with the service valves, remove refrigerant from lines and evap' and check the piston, flush again, purge, evacuate. Maybe remove the entire charge to eliminate the possibility I have contaiminated the refrigerant, but I CAN"T buy that because I was meticulous in cleaning the lines and pulling a vacumn.