Low side freezing - Refrigeration-Engineer.com forums

Niyo · #1 07-11-2009, 01:41 AM

My main A/C system's (Marine grade, sea water condenser, 16 ton) low side from the TXV to the compressor is freezing up during the night/morning on the vessel I work in. It happens within minutes so it makes it very difficult to catch before it becomes critical. We normally run it around 240 psig high side and 53 psig low side. Once that certain time hits the high side will drop to 220 and low 38 causing it to frost over.

I just shut it down and let it sit for about 30 minutes to dethaw then turned it back on, it dropped back to the pressures at which it freezes then slowly climbed back up (I believe because of the increased heat in the vessel's air). I am still fairly new to refrigeration and troubleshooting, my senior's believe it is a faulty txv or the drier/filter. I wanted to ask any of you if there is any other possibilities before replacing the txv.

Gary · #2 07-11-2009, 02:18 AM

The pressures don't tell us anything if we don't know what refrigerant is in the system.

And the very first thing you should check is airflow.

What are the temperatures of the air entering and leaving the evap coil?

Niyo · #3 07-11-2009, 02:43 AM

R-22 refrigerant and the air temps going into/out of the evaporator is in:72 out:64 Fahrenheit.

Niyo · #4 07-11-2009, 02:45 AM

Oh ya airflow is good

Gary · #5 07-11-2009, 02:50 AM

Next check the subcooling. We need to know the liquid line temp near the receiver outlet, the liquid line temp near the TXV inlet and the current high side pressure.

Niyo · #6 07-11-2009, 03:12 AM

txv inlet is 86 degrees, receiver outlet is 55 degrees, and high side pressure is 225 psig

Gary · #7 07-11-2009, 03:22 AM

I assume we are talking degrees F, not C?

Niyo · #8 07-11-2009, 03:27 AM

Yes F not C, I apologize. I am tired.

Gary · #9 07-11-2009, 03:32 AM

The system has plenty of refrigerant... if anything maybe too much.

Now we need to check the superheat. We need to know the suction line temp at the TXV bulb and the current low side pressure.

Gary · #10 07-11-2009, 05:46 PM

Quote:

Originally Posted by Niyo

txv inlet is 86 degrees, receiver outlet is 55 degrees, and high side pressure is 225 psig

I would insulate that liquid line. It is picking up way too much heat along the way. This is not the cause of your problems, but insulating the line will increase efficiency.

At this point the primary suspect is plugged inlet screen on the TXV.

Niyo · #11 07-11-2009, 07:44 PM

thank you, alot of my responsibilities are on the job and I greatly appreciate the help/knowledge

Gary · #12 07-11-2009, 07:57 PM

I'm wondering why the receiver outlet is so cold. Is the room temp that cold? Is the condenser outlet that cold?

Niyo · #13 07-11-2009, 08:02 PM

The vessel's house air is approx 60ish-70ish degrees Fahrenheit. We tried adjusting the thermostat up to allow the compressor some breaks in between freezes but on a vessel the crew is not to happy when they are sweating. The temp of the space that the 16ton is in is in the 80-90's.

Gary · #14 07-11-2009, 08:06 PM

What I'm wondering about is how that receiver outlet got to 55F? The only way that line temp could drop lower than its surroundings is if it is restricting. What is the liquid line temp at the condenser outlet?

Niyo · #15 07-11-2009, 08:26 PM

I am retarded, our accumulator is right next to the receiver, same shape and everything but condenser outlet is 78 degrees F and receiver outlet is 90 degrees F. I hit the accumulator outlet the first time

mad fridgie · #16 07-11-2009, 09:09 PM

Many boats us AEV (AXV) not TEV (TXV) can you confirm that you actually have a TEV (has a sensor bulb on the evap outlet)

Niyo · #17 07-11-2009, 09:12 PM

yes the sensor bulb is on the evap outlet

mad fridgie · #18 07-11-2009, 09:19 PM

Good, Do you have a control valve on the water at the condensor (small pipe form compressor or condensor is also connected)

Niyo · #19 07-11-2009, 09:21 PM

ya if it still works, this system is old and needs upgraded

mad fridgie · #20 07-11-2009, 09:28 PM

Quote:

Originally Posted by Niyo

ya if it still works, this system is old and needs upgraded

From what you have indicated I would say you have a problem here.
What I want you to do is to wind in this valve (along way) this will make your head pressure rise. (if not totally goosed) If it does make a presure difference, then wind in and out, then reset.
Reduce the water pressure entering the condensor slightly.

Niyo · #21 07-11-2009, 09:40 PM

I will have to try that tomorrow unless I get woke up tonight over the low side freezing. I believe that valve may need some work to cooperate. Thanks.

mad fridgie · #22 07-11-2009, 09:51 PM

If you are lucky it may just be seized.
More than likely the seat is "drawn" (lots of scratches) which is allowing to much water through. Good luck?

Gary · #23 07-11-2009, 10:46 PM

I'm still betting on the TXV inlet screen.

Niyo · #24 07-11-2009, 10:52 PM

Quote:

Originally Posted by Gary

I'm still betting on the TXV inlet screen.

I bet your right, we are trying to get a new condenser fabricated since we cannot buy a replacement (to out of date), so when we do that we are taking out the TXV. Just trying to see if there are ways to manage this problem a little easier or else anything else we have left out of our T/S. Thanks everyone for the help.

Magoo · #25 08-11-2009, 12:24 AM

Chilled water regulation control at plant room not fine enough, check dead band control. Step unloading is not reacting quickly enough, so chilled water temp drops and suction pressure drops and you risk freezing chiller HX, being an older system the controls will have been played with by everyone twisting knobs etc., start again and re-commission system controls, double check condenser water control valves and regulators as well.