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Old 12-07-2020, 20:10   #1
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liquid floodback on dual box 110V refrigeration

I have a bit more complex system than I wanted to have.


Two boxes with their thermostats. Freezer set at 24F with 3F differential
Fridge set at 45F with 3F differential. Refrigerant is R134A

1/2HP 110V compressor is mounted on condenser tray to which i added 1/2 ton water coil. Leaving compressor, refrigerant goes into water cooling heat exchanger, then into original tray foils with fan blowing over them. After that I have a receiver with king valve, then two packless valves with dryer and then a sight glass.

1/4" liquid line has a tee, and right after the tee, solenoid valve is controlled by a fridge thermostat. This valve controlls fridge evaporator plate with sporlan FJ 1/4C TXV

Freezer thermostat controls the compressor, fan and water pump power.
So I could have fridge solenoid ON and open with system not running. But when freezer thermostat is off, the system is off.

Two times in the last week i had liquid flood back to compressor at the time fridge set point was reached and freezer was still running. I did not add a suction accumulator but I did order it and I plan to install it.

Since I still had gauges connected I noticed that at the time of floodback, with fridge loop off, my suction pressure was 10PSI. Typically with freezer working from 24F to 27F, and fridge off, my suction pressure is at 0PSI. When fridge line opens, that pressure is around 5-10PSI.
Thermostat sensors are NOT mounted on evaporator plate. instead they are about mid way up the very deep boxes and on opposite side from evap plate. Not sure if this is correct or not?

Fridge TXV is new but I did not replace the freezer TXV so that is original from an unknown origin. I could not make the markings on it, but it has 3/8" inlet and 1/2" outlet. even though line going to it is 1/4". it just has a bigger flare nut.

R134A was used before so i imagine that TXV is appropriate. I did look at the inlet screen and it was free of debris.


before I replace a freezer TXV and add suction line accumulator, are there any suggestions on my hypothesis that as fridge shuts off, liquid refrigerant floods the compressor via freezer TXV. Both TXV bulbs at 1 o'clock position with copper line about horizontal. They are wrapped in pipe foam insulation with zip ties.

Is there something else I should be checking?


I thought maybe raw water strainer was clogged but I am not so sure anymore. That would cause higher high pressure line. That pressure typically remains around 85-100PSI. Its measuring already cooled refrigerant.

Compressor discharge line is hot, cannot touch it, but after water loop and fan, at the receiver it is already very cool. 1/2ton was smallest water loop i could find.
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Old 13-07-2020, 17:43   #2
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Re: liquid floodback on dual box 110V refrigeration

What is the superheat?
Why is the freezer set so warm?
When the system is off the refrigerant will migrate to the coldest place it can find, which can cause floodback.
Many of these systems have check valves on the suction lines just past the plates.
Compressor model?
The discharge line should be hot, that's ok.
In the picture it looks like the suction line is frosted past the valve, but not to the compressor, how long was it running to get to this point?
The TXV might need a little tweak to fix it, but i would start with the superheat number and go from there.
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Old 13-07-2020, 19:05   #3
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Re: liquid floodback on dual box 110V refrigeration

freezer is at 24F but sensing bulb is not against the plate. Its on the opposite side of the freezer box about mid way up. I guess I should move the sensing bulb to the plate itself.
I just took an IR reading. Bottom of freezer plate is -5F Top of freezer plate is about 15F. thermostat is showing 24.2F so system is OFF at the moment.



I know friday afternoon, I fired it up after re-charging. Freezer reached set point sometime overnight and it started typical cycling saturday morning. Freezer Thermostat is cycling between 24F and 27F. That keeps stuff frozen pretty well. I did not see frost shown in the picture during the weekend. Sunday evening, it happened. I heard compressor grinding, and noticed the frost. Fridge loop was off when it happened. I let some refrigerant out, and adjusted fridge set point to force it back ON, and frost line started retrieving. But it was still causing compressor to make grinding noise every now and then. I shut it off for about an hour. After I restarted sunday night around 11PM, its been working fine almost another 24H now.

I don't have check valve. Doesn't check valve prevent flow in opposite direction? So I dont get how checkvalve would prevent flooding. Are you saying flooding can happen after the system cycles to OFF state?



I also did notice that raw water strainer had debris after I had shut the fridge off to let the frost line retrieve. Not sure how obstructed the water flow was, and I had also taken off the high side pressure gauge so i did not have that reading.



compressor is QE 1/2HP QCF-12A it is 1200BTU 110V.
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Old 14-07-2020, 19:39   #4
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Re: liquid floodback on dual box 110V refrigeration

!/2 HP compressors are normally producing 3400 Btu at +10 degrees F. What size Btu orifice is in freezer TXV? and The way those boxes refrigerant flow is controlled refrigerator TXV would be smaller orifice than than freezer. You could maybe adjust the freezer TXV to reducing reduce flow. This would be the standard method but still create frost approaching compressor at only compressor start up until TXV's begin to react to superheat adjustments.
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Old 15-07-2020, 09:50   #5
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Re: liquid floodback on dual box 110V refrigeration

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Originally Posted by Richard Kollmann View Post
!/2 HP compressors are normally producing 3400 Btu at +10 degrees F. What size Btu orifice is in freezer TXV? and The way those boxes refrigerant flow is controlled refrigerator TXV would be smaller orifice than than freezer. You could maybe adjust the freezer TXV to reducing reduce flow. This would be the standard method but still create frost approaching compressor at only compressor start up until TXV's begin to react to superheat adjustments.
Thank you. I dont know the orifice to freezer TXV. Reduce flow means clockwise? on the screw that is at the side. I think my freezer txv is danfoss. see pic.
I am putting a suction line accumulator, and would that resolve the liquid floodback if I don't succeed with adjusting freezer TXV?
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Old 15-07-2020, 11:16   #6
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Re: liquid floodback on dual box 110V refrigeration

I can not tell if that is a Danfoss TXV. The TXV temp sensing bulb should have insulated rapped around bulb and tube this will do the same as adjusting valve to reducing flow. If Refrigerator bulb is the same poor heat conduction to line insulate it as well. Refrigeration supply stores and some auto stores carry this cork thick playable insulating material in a roll it can be rapped around or worked like putty.

Coolerking is correct if you have large eutectic plated a suction line is a must because once plates are frozen and compressor stops all refrigerant in system will try to reach the cold plates. On the next compressor start refrigerant now in liquid form will be drawn direct to compressor. Installation of suction mine accumulator where the phase change back to vapor gas will occur preventing damage to compressor.

The major problem causing compressor failures on those compressors in marine application is failure to adequately cool compressors.
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Old 15-07-2020, 19:50   #7
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Re: liquid floodback on dual box 110V refrigeration

Thats very great info. thanks. That pic is from before I put it into service. I have wrapped the bulb and line in thick refrigeration pipe foam insulation that i slit along one side. I put two zip ties on each end.

Compressor is running very cool. I have an oversized (1/2 ton) heat exchanger, Im in RI. I can keep my hand on top of compressor at all times. Discharge 1/4" line is too hot to touch but as soon as it exists heat exchanger is feels like its cabin temp.
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