Freezer not quite getting cold enough

[nafets47]

Does the freezer defrost run often enough. I ran into this issue where the defrost was not happening consistently enough and the freezer wouldn’t get below 0.

Also is your freezer spec’d to go that low?

[fixbear]

First, be aware that there is no standard for walk in freezers. If it will hold below 32F they can call it a freezer.  This forces us to always evaluate the design when we run into a unknown one.  Box, insulation, usage and heat loss all come into play. Easy to determine the BTU’s of the evaporator and condenser by model. There are quick charts for needed BTU’s.  More often than not in my area I’ve found condenser undersized for a good freezer. One your feet stick to the floor.  And they should run 20 to 22 hours per day. The old hot gas defrost ones never stopped. 

Quick troubleshooting is to look at the evaporator from the back and note frost amount and coverage. Then feel the liquid line coming in.  And the fans.

You now know if you need gauges and temp probes. 

Why;

If the liquid line is warmer than outside ambient-  Condenser problem

If the frost is un even, charge or metering. Check superheat and compressor loading with a amp meter. I’ve seen many were the charge rusted a pin hole and reduced the capacity.

Ice build-up on bottom;  Defrost system.  Time, heaters

Fans;  If one has a hub loose or motor not to speed, flow across the evaporator is not right  Take your pocket digital thermometer and check incoming air and outgoing air temps. should be a bout 10 degrees difference.  I’ve seen where they all look like they are running, but in reality one was running backwards.  Just pulling air in and out the front.

[frank67]

Hi! Olivero

The first thing to check is your super heat!

You may have to adjust your txv and if it’s not adjusting replace the txv.

Temp setting for ice cream is -10*

[olivero]

Sounds good guys. 

I might have just been stupid, I went up and saw it was off, so I turned the temp down some more, T-stat says -10*F but it was 0, I’m thinking it has a differential setting on the T-stat which may be the problem, so I set it lower and now I’m letting it run.

Approach temp on the condenser is about 4*F so it’s condensing properly. 

[fixbear]

Frank67, we never want to enter a system if it is not necessary.  We introduce contaminates even though we try not to.  By checking head temp, tail temp and load we can get a Idea of what may be happening.  TXV’s In walk in’s rarely fail.  90% are Sporland. But the other brands are a different story. But TXV charges do.  And Brazed in valves take a bit to change.  In 50 years of working on them, I only saw one true failure.  And that was because the installer used solder and a surplus of it weeped into the actuator piston and port.  The other one that I saw fail, was not a cooler, but a de-humidification  kiln. And that was from foreign particles with a 4620 filter dryer. Other techs that I know and trust from RSES have only seen true failure from lack of oil circulation.

[olivero]

Interesting, I don’t normally tap into the system but I got these Tiesto or whatever bluetooth gauges, the stubby ones, so I don’t feel too bad about doing it now, I think it’s almost impossible to contaminate the system with those since there’s no hoses or anything.

[fixbear]

True on that.

The biggest problem I always found with metering was the bond between the sensing bulb and the tail coil. Often corrosion or a loose clamp.  Hard to see under the insulation.  And they should be insulated to help cut down on the drift.  For a while with some brands the copper straps were Actually copper plated steel.  As were the screws and nuts.. You’ll know when you run into one as you will have to cut it off.

When I first got into refrigeration full time, I bought what I thought I would need in Expansion valves for everything from 1/4 hp to 5 tons.  Low temp, medium temp and a couple high temp.  I still have all but one in stock.

[olivero]

Very true.

I’ve had a couple of TXV’s go bad, either from leaking refrigerant at the spot welds, particularly Danfoss TXV’s but otherwise, I’ve seen 2 or 3 go bad.

[beef]

Is the Txv internally equalized or externally equalized. External will be fine to replace internal, but internal can’t replace and external. Always gotta verify proper charge and solid column of liquid to start thinking it’s a TXV. And most manufacturers say the TXV shouldn’t be adjusted and if you have to, you prolly have the wrong one. 

[olivero]

Depends on the unit, what kind it is, I’m not sure what this freezer uses, never needed to look at it.

That is very true, solid column of liquid is very important, normally people adjust them or try to when there’s a leak and it’s low on gas, where you end up not having a solid column. I’ve done that before, until I realized what I was doing was wrong.

[fixbear]

Always check the dryer for a temperature differential across it if there is no sight glass.  Especially with a conversion of refrigerant or compressor replacement. I’ve come across undersized lines as well.  And there is always the line that got hit somewhere s and is restricted. 

BTW; Walk in freezers usually have a pressure limiting charge to protect the compressor from overloading.  In the early stage of start up before the box cools down the evaporator will be starved a bit.  This is normal.  But it definitely slows the take down of the box.  With TXV adjustment of freezers you should always have a ammeter on the compressor to monitor the load.  You can destroy the compressor if it isn’t a pressure limiting valve.  Been there, done that with a 12hp Bristol.

[beef]

To me it sounds as if maybe you have a system maxing the TXV capacity.

If the spring tension plus the evaporator outlet pressure are greater than the sensing bulb pressure, the orifices is moved to a more closed position, throttling back the flow of refrigerant.

Maybe tweak it 1/4 loose and see if you can get a little more refrigerant in there, but most likely increasing the evaporator pressure and still maxing out the txv capacity. 

Are you sure the evaporator isn’t oil logged???? If I recall correctly you mention the compressor was changed out, may have gone bad due to lack of oil, and that oil might be sitting in the evaporator. 

[olivero]

Well, it turns out it’s not really a problem, unit was at -6*F when I saw it, must’ve just been an offset on the thermostat confusing me to think it should be colder.

[fixbear]

Or your visits are just after it comes out of defrost. 

[olivero]

That would be typical of me.

[fixbear]

HE HE.  Love it.  Been there

[isitfridayyet]

Definitely superheat first, assuming pressures look relatively normal. I would suspect a txv adjustment, or maybe weak compressor valves. I’ve seen especially on low temp equipment and ice machines where it’s not noticeable at first glance, because the pressure is pretty close, but will hit a point where it just won’t drop that extra psi or 2 that it needs to get there. Especially if it has a history of freeze ups, or maybe the condenser fan went out at some point and did some damage (I know yours is water cooled, so that wouldn’t apply).