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Discussion Starter · #1 ·
Ok so been in hvac (mostly residential) for a long time never really messed with wall in freezers or coolers until my new job. Since starting I have trouble shot and installed a couple systems but now me and my partner are stumped. A few weeks ago we get a call the institutions main freezer is downer go out there system A ( the main load) one condenser one evap tripped on the oil control so we put a request in for oil and a oil pump the institution did not have one for us to use. checked systems b&c both 2 evap to one condenser were operating normally other then needing defrost heaters so we put a request in for them as well and we shut the freezer down and call in the freezer trucks. While waiting for approval someone in food service calls outside contractors in Who decided B needed to be leak checked (removed all refrigerant) and the other had wiring issues and needdd a new time clock( seems now the fan delay was not engaging the fans) and is what is listed on the work order. Now C keeps short cycling due to low pressure so I’m sure if they took refrigerant from that unit.
Now the in-house guys, us, have to play clean up and guess and check what they did and get this up and running. We get the oil in A and off she goes pressure was around 22 we wanted to get the other systems working and the box to temp before checking superheat. We started with the unit that just going off on low pressure and inside the door in old sharpie says approx 34lbs r404 so we start filling we have now added close to 50 lbs of refrigerant and it still seems grossly under charged 0psi suction 160 liquid with a superheat inside at one of the heads at 54 at the condenser at 93. We don’t want to keep adding but I don’t know what else to do. We still have to find the leak in the nitro one and charge that too…

system was installed in 2000
No headmaster
Yes receiver
Standard txv

Coil only getting frost on the first 1/4 of the evap.
The condenser sits out side
the unit that is currently now operational was running at 22 suction and 200 liquid
Indoor evaps are bme190
Condenser tags faded to bell

please help or I will go bald soon 🤪
 

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1 may have gone out sometime ago, but with all units working, it didn't effect the temp of the box. Could also be a restricted LLFD.

Can try putting the TXV bulb in hot water and see if pressure rises. But if the LLD is restricted, it will still act like a bulb lost its charge.

I take it for granite that the sight glass is clear.

I'd probably recover the entire charge, replace both TXVs and the LLFD, vacuum and recharge the 34 pounds that was written down. Restart that unit and make sure sight glass is clear and check SH.
 

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Discussion Starter · #5 ·
1 may have gone out sometime ago, but with all units working, it didn't effect the temp of the box. Could also be a restricted LLFD.

Can try putting the TXV bulb in hot water and see if pressure rises. But if the LLD is restricted, it will still act like a bulb lost its charge.

I take it for granite that the sight glass is clear.

I'd probably recover the entire charge, replace both TXVs and the LLFD, vacuum and recharge the 34 pounds that was written down. Restart that unit and make sure sight glass is clear and check SH.
Thanks I’m gonna start that process on Monday. I know on residential units I can check a filter dryer by taking a temp differential as long as it is within a degree it was ok is this the same? Getting parts are a hassle just trying to rule things out if I can test it. The sight glass was clear seems after talking to a bunch all signs are pointing txv. My only head scratcher is why would my discharge pressure be low as well160 where an operating unit next to it is at 210. Just trying to learn thanks for your insight
 

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With little refrigerant flowing through the evap, there is not much heat to get rid of, so head stays low.

A LLFD can have a large pressure drop and not have any temp difference across it.

Get out a PT chart for R22. Lets say its 95°F outside. And the head pressure at the service valve is 260PSIG. And you have 12° of SC. If the LLFD has a PD of 34 PSIG across it. The saturated temp of the R22 is 110°F, so you won't see a temp drop until the restriction has a 50 PSIG or greater pressure drop across it.
 
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