problem with walk-in cooler pumping down

[Buddy Lee]

Hey guys, I have found a few answers to some problems in the past over here, but I cant find anything for this problem so I thought I would register and ask the question myself
I am a commercial tech with a bit of refrigeration experience. We have a restaurant that has begun having some problems with their walk-in and I am not sure what to try now.

Our customer has an older building and his walk-in freezer was waterlogged and the walls were buckling out and causing him a mess with ice on the floor. He decided that he did not need his freezer anymore and put in a deep freeze and a few standup freezer and got some guys he knew to tear down the old freezer. They did this on a Saturday (I had no idea it was happening) and Sunday morning I got a call from him about the cooler.

Apparently the guys he hired must have done something to the cooler (no one has gotten a straight answer yet) because he was telling me he had a leak(I never found a leak in the system). In a panic he called a guy he knew, because I was separated from my phone on Sunday morning for a few hours. It was a 409a system and the guy he called dumped in a bunch of 134a and told him it would hold him until I got there. Once I arrived, I recovered the refrigerant, replaced the drier and pulled a vacuum and charged with new 409a. Things looked good but he called me Tuesday and told me it wasn't working anymore. I returned and the unit was pumped down, but the solenoid valve was open. It eventually cleared and began running properly, but after a few more days, it pumped down again and would stay pumped down for several hours before clearing and running.

After replacing the TXV and the solenoid vave, I took them apart and found no visible flaws, and the strainer in the TXV was clean. Well, I have no idea what the problem is, but every week or so, the cooler will just pump down for 3-5 hours and then begin working properly. I feel confident that there is no moisture in the system due to the drier replacements and the multiple vacuums I have pulled. I am beginning to wonder if someone has put some leak stop in the system at some point and that is causing the problem. I think my next step is to do an oil change on the system and try blowing out the lines again, but I feel like I am spinning my wheels.

Anyone have any ideas or seen this before?

[leslie cook]

Is the low pressure switch closing?

[Buddy Lee]

The low pressure switch is functioning properly. There appears to be something in the refrigerant line causing a restriction every few days, but the strainer in the txv was clear and the drier was not stopped up. When I replaced the solenoid valve, I also saw nothing to indicate a problem.

It is just that every 3-7 days, the system pumps down(solenoid energized, and appears to be functioning) and stays pumped down for a few hours.

[Phase Loss]

One time I found a rubber plug stuck inside a 90.

it caused intermittent pump downs.

[Dchappa21]

Could be the T-stat is wacked out.

[Dchappa21]

....... Or the defrost clock

[trippintl0]

Had three like that before. One had a loose wire in t-stat that was in the terminal but not actually under the screw (a ranco ETC) that would randomly shut off the box. Found by wiggling wires.

The other had a defrost timer that would randomly stick (paragon mechanical timer).

The other had moisture in TXV. I used a propane torch to warm it up and it started flowing again.

The key is to be there when it fails! Good luck, sounds frustrating.

[2sac]

The other had moisture in TXV. I used a propane torch to warm it up and it started flowing again.

The key is to be there when it fails! Good luck, sounds frustrating.

I agree with this

[K_Neil]

It's amazing how many machines start working when the mechanic shows up

[Buddy Lee]

We pulled the refrigerant, and pulled all components and blew the lines out with nitrogen. I didnt see anything but after the vacuum, the unit took 5 less lbs of 409a. Hopefully something was blown out, the fact that it took less refrigerant shows that something has changed, I hate not knowing for sure but time will tell. Gonna be stopping by the place when possible to check.

[phxhvac]

Check low pressure switch, sollenoid valve (sticking?), intermitent restriction in metering device.