# Humidity level in a frost free freezer



## wptski (Sep 19, 2008)

I've searched the subject but found some saying that it can be high and other say it's low.

A bit technical but has anyone logged humidity in a frost free freezer? I know they do this in large commercial walk in freezers.


----------



## rjniles (Feb 5, 2007)

Cold air holds little moisture. Any humidity in a freezer condenses and shows up as frost.


----------



## wptski (Sep 19, 2008)

rjniles said:


> Cold air holds little moisture. Any humidity in a freezer condenses and shows up as frost.


Yes, I know that but some frost is normal that's why they defrost but how much RH is normal? I know that it will vary but should it be around 25%, 50% or 75%?


----------



## Bud9051 (Nov 11, 2015)

I'm going to take a guess at something close to 100% due to the cold temperature. If you open the door and the freezer fills up with 70° air at 35% RH and it then cools to 30° with the door closed the RH will jump to 100%, 150% on the calculator. As the inside temp drops close to the dew point the RH approaches 100%.

Bud


----------



## Nestor_Kelebay (Jun 17, 2008)

I'd say that theoretically, the RELATIVE humidity inside a frost free fridge should be 100%.

That's because the circulating air is always passing over the frost on the evaporator coils. If the relative humidity is less than 100%, frost will sublimate to raise the RH to 100%. And, as long as the air inside the fridge is cooling down, the relative humidity in that air will remain at 100% as it's temperature drops and moisture collects on the evaporator coils in the form of frost.

So, no matter which way you look at it, the relative humidity inside the fridge should always be at 100% (in my view). That would be different in the minutes after opening the fridge door, but it should always stabilize at the fridge and freezer temperatures with a RH of 100%.


----------



## wptski (Sep 19, 2008)

The reason I'm asking is because I recently worked on an old fridge, the thread is below somewhere. The condensation wasn't draining for whatever reason, iced up and was dripping from the top inside the normal food compartment(top freezer model). It runs down the back wall into a sloped bottom but it never had a way out of there into the evaporation pan below that.

I had to sponge out water from the inside before and I have provided a way out to the evaporation pan.

I wasn't seeing any water but I figured that was because of the winter dryer air but then it started to drip inside. So that's fixed for the time being but I'm wondering if I should or shouldn't see water running down the back wall. I'm not seeing that much front built up the metal fins.

So I've logged the freezer and here is a graph showing two defrost cycles.


----------



## Nestor_Kelebay (Jun 17, 2008)

You should NOT see water dripping into the fresh food compartment of a frost free fridge.

If you do, the problem is most likely a clogged evaporator pan drain.

Below the evaporator will be a pan that slopes toward a drain hole. Melt water that drains into that hole will be directed onto a pan at the bottom of the fridge where the heat from the compressor will cause that water to evaporate back into the surrounding air.

It's common for that drain hole to get clogged up, and when that happens, the melt water from the defrost cycle has no where to go. As that water accumulates in the drain pan under the evaporator, it eventually overflows the drain pan and ends up dripping into the fresh food compartment below.

You just need to clear that clogged drain in the evaporator pan.


----------



## wptski (Sep 19, 2008)

Get this! There wasn't any way for the water to get out because there wasn't any hole on the inside. It has a double wall with some insulation in between. Now from the bottom there was a large hole. Looking at my other fridge in my basement, it has a float like assembly.

The problem fridge is about 35-40 years old and nobody can remember any water accumulating on the inside before.

I took apart the freezer, thawed the ice and drill a hole in the bottom. I used a plastic tube which I chaulked in place.

The water can drain but at the moment, not enough from the defrost cycle is running out.

This is why I'm asking about the RH in freezer. Has it plugged up already again as shown by the high RH is is that normal for that small compartment and the air is too dry?????

I'm going to try and log my sister's fridge to compare.


----------



## GrayHair (Apr 9, 2015)

wptski said:


> ... The problem fridge is about 35-40 years old ...


Personally, I much prefer repair over replace, but I also keep on eye the point of diminishing returns. Maybe it's time to retire that fridge.


----------



## beenthere (Oct 11, 2008)

On a small freezer that has good door seals. There isn't very much moisture in the air, even after opening the door. So very seldom does any moisture need to be drained. It usually freezes on the product packages in the freezer after a defrost cycle.


----------



## wptski (Sep 19, 2008)

beenthere said:


> On a small freezer that has good door seals. There isn't very much moisture in the air, even after opening the door. So very seldom does any moisture need to be drained. It usually freezes on the product packages in the freezer after a defrost cycle.


This happened before in the summer of 2013 but I missed the fact that the drain hole was missing. During this past summer the bottom of fridge where the drain hole should would fill with water which I had to sponge out. I can't remember if that ceased during the dryer air in the winters since 2013.

The RH in the fresh food area of the fridge runs from 20-25% when the door is kept closed.


----------



## AllanJ (Nov 24, 2007)

Wait until summer.

While the RH (relative humidity) of the air as it passes through active cooling coils can go to 100% (temperature around 0F), the RH drops for the air circulated into the main compartment (temperature around 35F). In winter the RH inside may be low enough that the amount of frost accumulating on the coils evaporates completely during the defrost cycle.

When warmer air enters the freezer compartment, either through the open door or during the defrost cycle, the items in the freezer will exude cold (or suck heat) possibly causing frost to form on the packages. In some cases the surface of the food thaws (and then refreezes after the defrost cycle) and after repeated cycles this can deteriorate the quality of the food.


----------



## wptski (Sep 19, 2008)

AllanJ said:


> Wait until summer.
> 
> While the RH (relative humidity) of the air as it passes through active cooling coils can go to 100% (temperature around 0F), the RH drops for the air circulated into the main compartment (temperature around 35F). In winter the RH inside may be low enough that the amount of frost accumulating on the coils evaporates completely during the defrost cycle.
> 
> When warmer air enters the freezer compartment, either through the open door or during the defrost cycle, the items in the freezer will exude cold (or suck heat) possibly causing frost to form on the packages. In some cases the surface of the food thaws (and then refreezes after the defrost cycle) and after repeated cycles this can deteriorate the quality of the food.


From what you and "beenthere" have stated, all might be normal for this time of the year. I just dropped my logging device off for my bro-in-law to log their fridge so I'll get the results in a day or two and compare.


----------



## wptski (Sep 19, 2008)

Got the following graph from my bro-in-law from their freezer of their fridge. It seems my RH is comparable but what's all those fluctuations from 2F to -4F every minute?? Is this normal for a modern fridge and I wonder how it's done also? I know that normally, dehumidifiers and AC compressors can't be cycled that quickly or you start with a high load. Thermostats normally have or did have a feature where the compressor has to be OFF for at least five minutes before it allows it to cycle ON again.

It seems this one has a variable defrost interval cycle also because another graph shows a defrost cycle in the middle of that same time frame.


----------



## beenthere (Oct 11, 2008)

Could be the door/shutter to for the fridge opening and closing to keep the fridge at temp.


----------



## wptski (Sep 19, 2008)

beenthere said:


> Could be the door/shutter to for the fridge opening and closing to keep the fridge at temp.


Would you care to explain what that is?


----------



## beenthere (Oct 11, 2008)

Some fridge freezers set up have a shutter besides a fan that moves to control air flow to the fridge. If that one has one, it could be moving.


----------



## wptski (Sep 19, 2008)

If it does and it's moving, it's constantly and seems rather dumb. You have any idea what the point of it is?

My fridge has three large rectangular openings hear the door that connect the freezer to the other compartment. In fact, when it starts to drip, that's where moisture forms.

EDIT:
Looked that up. I assume that the freezer is cooled and some cooled air is diverted to the fresh food compartment by the shutter. This makes sense but constant movement doesn't.


----------



## beenthere (Oct 11, 2008)

wptski said:


> If it does and it's moving, it's constantly and seems rather dumb. You have any idea what the point of it is?
> 
> My fridge has three large rectangular openings hear the door that connect the freezer to the other compartment. In fact, when it starts to drip, that's where moisture forms.
> 
> ...



You may or may not have a shutter that moves. You'll have to double check that.

Shutter would close so that the fridge doesn't become freezer.


----------



## wptski (Sep 19, 2008)

beenthere said:


> You may or may not have a shutter that moves. You'll have to double check that.
> 
> Shutter would close so that the fridge doesn't become freezer.


That's a Frigidaire FRS26ZGE which I can't find anything about. I had a new Frigidaire in mind and in all of its documentation makes no mention of a shutter, etc. Since that Frigidaire FRS26ZGE is a bit old itself maybe a shutter wasn't used back then either. I'm just curious which comes from my background in maintenance.

I'll be going over there tomorrow to pick up my logging device so is there an easy way to tell without taking it apart?


----------



## beenthere (Oct 11, 2008)

Don't think so.


----------



## wptski (Sep 19, 2008)

Thanks!

My bro-in-law sent a few more files. His fridge is stranger than mine for sure. I wonder what could cause for the DP and RH to spike like this in the fresh food compartment? From beginning to the end is over thirty minutes and the start to peak is ten minutes.


----------



## AllanJ (Nov 24, 2007)

Some refrigerators have separate controls for the freezer compartment and the main compartment where the freezer control is a thermostat and the main compartment control links to a shutter between the two compartments that lets more air or less air circuilate through..

Adjustment is a trial and error process (more correctly an iterative process) where you need to adjust one control and then the other and then the first, etc. until you get the temperatures to your liking.


----------



## wptski (Sep 19, 2008)

AllanJ said:


> Some refrigerators have separate controls for the freezer compartment and the main compartment where the freezer control is a thermostat and the main compartment control links to a shutter between the two compartments that lets more air or less air circuilate through..
> 
> Adjustment is a trial and error process (more correctly an iterative process) where you need to adjust one control and then the other and then the first, etc. until you get the temperatures to your liking.


Yeah, I was reading the manual on that new one I was looking at and it stated when you made an adjustment to one check the other but in its documentation, no mention of a shutter.

My old one upstairs just has three large slots connecting the two compartments and while adjusting I noticed that one affects the other. It also has two controls.


----------



## beenthere (Oct 11, 2008)

Someone may have opened the door for a minute or 2 while he wasn't near it to see.


----------



## wptski (Sep 19, 2008)

beenthere said:


> Someone may have opened the door for a minute or 2 while he wasn't near it to see.


No, he was home alone but he wasn't sure if it was opened during the logging. I believe I know the reason why as I've run into this before. I've sent an email to verify this but I'm sure that it uses a thermistor for measuring temperature and they are slow to react.

I used another device I know uses one and got the same results on my fridge with both devices. Opening the door for a full minute should show up but I only opened the door for twenty seconds. I have another thermometer that uses a K-type bead and it does react as the door is opened.


----------



## wptski (Sep 19, 2008)

The logger doesn't use a thermistor but a combined temperature and humidity sensor but has the same issues where the physical mass of the logger becomes a thermal store so reacts slowly to temperature changes. That was in their response I received today.


----------

