Supermarket suction line frosting

[mccoolair@yahoo]

Encountering problem with suction line frosting on startup of an old Tyler Produce display case after repairing leak in suction line. While charging in refrigerant (R22), the frost starts at evaporator(approx. 80' lineset), and travels back to the compressor. It's a med temp system, of course, consisting of 2 - 12' cases. Oil level is at the top of glass and goes down to bottom of glass within a minute after startup. I suspect this is somehow related to the rapid frost buildup. Ambient at the time was 55-60F. Crankcase heater is working but the frost forming on the compressor negates its effectiveness. Suction pressure pulls down to 30psi, and adding more refrigerant will not bring the pressure up. Looks like a restriction to me because of the low pressures, or low airflow in the display case. however; the fans are running and the coils are unobstructed.

[750 Valve]

Are the txv's set correctly? Is there a suction line filter/drier - this could be clogged and causing a pressure drop. Does the comp have an unloader thats not working properly? Is it just migration in the off cycle causing this?

[Toosh]

Hi mccoolair one thing you have not mentioned is what your superheat is, Have you checked it.

Norm

[Yusuf Ismail]

Hi mccoolair have you checked a expansion valve or one thing you have not mentioned is what your superheat is, Have you checked it ?

[Dr._Fleck]

You've got valve trouble matey.. Take the kick plates off the bottom so you can see the suction pipes coming out of the cases, switch on and the one that frosts up 1st put a new TEV on that case. It's a good bet that that will cure the problem.

I remember years ago at a COOP we had this problem on some freezer cases, we fitted all new TEVs and capsules, new refrigerant... cant remember how it was resolved:confused: hmm, i'll think some more:)

[tonyelian]

hi
it seems ur system is over charged.if ur evaporator is clean from ice start evacuating the load slowly until the frost is gone.
did u change filter drier &did a good vaccum.
u did not provide info.about ur superheat &subcooling so i &other members can figure the right solution for ur problem.

[chillin out]

after repairing leak in suction line.
You didn't heat the bulb for the TEV up too much did you?

Also, on some of them older cases they fitted a suction pressure thingy. Looking at it, it would look like a heat exchanger and is located in the case somewhere (on the suction out and liquid in). But it is actually a switch thing. I can't remember exactly how it works but it's something like 'when the liquid flows it pushes a magnetic thing inside which opens the suction fully.

If you flood the case with low temp liquid (partially boiling off) and then it hits this valve which could be stuck partially closed then the rest of the liquid will boil off from that point and cause floodback.

Chillin:):)

[Electrocoolman]

Hi, would we not expect to see a liquid line solnd valve (and a pumpdown system)?

I agree that a TEV could be misadjusted, but we are talking of frostback ON STARTUP, so refrigerant migration during off cycle is a possibility.

The fact that there was a leak on the system, could mean that the system had a system charge such that the evaps could cope with and absorb the migration. Adding refrigerant has highlighted the problem(s).