Original message
| ConAir
 |  "Walk-in freezer w/Larkin heat exchanger??"
, posted Wed 22 Oct 22:42  
I've got a walk-in freezer with 502 that when I showed up was going off on low pressure limit. Hi was 150psi and low was below 10psi(limit). I charged to 175 hi and 16 low. I ran fine for about 45min. and then the hi stayed up but low dropped out under limit again. Everything checks ok, solenoids, txv, replaced filter drier, etc... It has a Larkin heat exchanger mod. 480HE. The hi and low side go into this thing right before the txv. I haven't seen one before and was wondering if anyone here has.
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Replies:
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| Schock Therapy
| "Re(1):Walk-in freezer w/Larkin heat exchanger" , posted Thu 23 Oct 01:00
What is the box temperature? What is the evaporator temperature? What is the temperature of the discharge air? What is your suction line temperature? Is there frost forming on the tx valve or distributor? Is there bubbles in the sight glass?
Sorry to reply to your question with questions, but in refrigeration, there is a whole lot more to it than just pressure! A pressure reading is only relevant when it is paired with a temperature reading!
The Heat exchanger you describe sounds like it is being used as a liquid sub-cooler to provide good quality liquid to the tx valve. The added benefit of it is that it will superheat the vapour and hopefully boil off any liquid flooding back. It isn't likely to be causing your problem.
By the way, you say you are using R502? Where are you getting the stuff? It has been banned around here for YEARS! You should be thinking about a refrigerant retrofit!
It's only a shock if your not expecting it!
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| | ConAir
| "Re(2):Walk-in freezer w/Larkin heat exchanger" , posted Thu 23 Oct 19:41:
The 502 was in the shop so I'm using it up. The problem is I can't get it to run long enough to get temps on it. Everything is sized properly comp, evap, and txv. It seems as if it has a restriction, but the high side isn't too high. I'm just not getting it back on the low side. I replaced the filter drier and the txv is ok. It has that Larkin Heat Exchanger on it though. It runs fine when doing the hot gas defrost, but the txv and that heat exchanger thing are bypassed. I'm thinking about taking it out because that's the only thing I can think of that's restricting. It's a bronze/brass tube that the high and low go into by the evap. It's before the txv on the high side. I haven't seen one before. Anyone know anything about? Google search on it yielded no results. Thanks.
[this message was edited by ConAir on Thu 23 Oct 20:32] |
| | Schock Therapy
| "Re(3):Walk-in freezer w/Larkin heat exchanger" , posted Fri 24 Oct 02:40:
I think you would be wasting your time taking the sub-cooler out. There is very little that can go wrong with those. It is essentially a tube within a tube.
Are you sure the system isn't just low on refrigerant? your head pressure is low for 502. If the box temperature is warm, I would expect the suction pressure to be much higher. (I'm not clear on why you cant get temp readings...I assume you mean it is not getting cold at all!)
How do you know the tx valve is ok? If it is sticking, it can under-feed, and if the pressure element is rusty it may have lost some bulb pressure. Both problems would cause low suction pressure. Check for Frost forming on the outlet of the txv and distributor, those are signs of under charged system, or under feeding valve. Soak a rag in hot water and put it on the tx bulb; does the suction pressure go up? Pump the system down and disassemble the tx valve. Do the pins move freely?
If you jump out the pressure control, does the system pump down into a vacuum or does it keep running in the 0-10 psi range?
My first thought is that your system is still low on refrigerant, but if you have a full sight glass, then you should be taking a closer look at the TX Valve.
It's only a shock if your not expecting it!
[this message was edited by Schock Therapy on Fri 24 Oct 02:45] |
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