Danby DFF280WDB freezer OK, fridge too warm

[Cubytus]

Hello there,

I have this compact fridge in my apartment, and noticed that, at first it did not cool very fast, and almost never stopped running after that.

Upon further investigation, the freezer had no issue getting down to -18C, while the fridge stayed above 8 degrees C, way too high, before the freezer rose again to -10.

On removing the freezer back plate, I found tons of ice built-up on the coils. I tested the heater by plugging it on a programmable timer, and it works fine. The shutdown thermostat on the coils is apparently shut closed between -10 and +15C, so does not block current flow to the heater.

I tested what I could on the control board (C0937-ML, also used by Fridgidaire model FFHT10F2LW, it seems) and the very few times the fridge shut down by itself, I found 120VAC on the heater connector, otherwise a rather constant 2.7VAC.

Once, I accidentally left the fridge disconnected long enough for all the ice to melt, and it was able to recover adequate temperature in each compartment for a few hours before rising again the next day due to ice build-up.

Another time, the LED flashed very regularly when doorways opened, once per second. I thought about a possible error code, but there is no service manual available to the public. Disappeared after a power-cycle.

To the best of my interpretation, either the heater doesn't turn on often enough, long enough to melt the ice, or the fridge not shutting down often enough doesn't allow the heater to turn on, which only worsens the issue since ice can't be melted for improved cooling efficiency. Or, there is too much moisture-producing food inside the heater can't cope with.

The defrost thermostat apparently needs a replacement since I don't think it should stay closed over such a wide range of temperature.

How would I test the other components to find which, the board or the internal fridge temperature sensor is not working as it should? The board seems rather hard to find.

[johntech]

Ice build up on the evaporator coils should not build up to problem causing levels in a day.  If they are then I would suspect that the door seals are not keeping room air out of the unit. 

[Cubytus]

I can't be too sure about the exact time it took for the ice to build up since the task of repairing this fridge only adds itself to the normal household taks, but for sure it took only a short while. How would I test the seal, anyway?

[johntech]

Visually inspect door seals. Usually when I manually defrost an evaporator it will last between 1 - 2 weeks before it has cooling issues again. I remove all frost when I manually defrost. Could also be a incomplete defrost issue like the heater is not getting hot enough or the defrost terminating tstat is opening to early. The only way to test it is to pull the evaporator cover, put it into defrost and watch what happens. Not sure if yours has an adaptive defrost board or a defrost timer. They could also be at fault by not going into defrost on there own. I am not having any luck with your model number and not knowing what parts you have make me not much help.

[Cubytus]

The evaporator efficiency also appears to depend upon the size of the air inlets / outlets. On this compact fridge, the inlets/outlets are very easily blocked by ice build-up. I had to tape shut two of the three air openings in the freezer compartment and turn the knob to "min" so that the fan pushed more cold air toward the fridge instead. The Danby DFF280WDB is almost identical to the Fridgidaire FFHT10F2LW, as far as I could find.

I tested the thermostat in series with the heater: doesn't open even at +15C. I suspect it should open at a much lower temperature, yet its current malfunction doesn't prevent the heater from performing its job.

Strangely enough, the heater outlet on the control board provides a rather constant 2.7VAC most of the time, and climbs to 120VAC from time to time when the compressor is off. Apparently, this isn't enough to properly melt the ice. I also plugged the heater directly on an electronic timer, and it gives off a faint red glow, produces heat, and draws around 1.2A, matching the 150W rating of the heater. So the heater itself is working.

I read somewhere that Energy-Star rated fridges tend to use adaptive defrost rather than a fixed timer. In which case, how does the fridge "knows" when to issue defrost commands? Surely it needs some kind of feedback. 

What do you mean by "visual inspection"? There's no obvious sign such as a gap, missing portion of joint, or anything like that.

So far, I am sure the defrost thermostat needs to be replaced as it should open at a much lower temperature.

The control board, fridge thermostat and perhaps the freezer AND fridge door joints may all be responsible for the malfunction, but how do I test each of these? Spare parts are surprisingly hard to find, and expensive to deliver.

[johntech]

Adc boards use an algorithm to decide when to defrost. They monitor compressor run time, door openings, evaporator tempretures and so on to determine when to defrost. Typically if you have a good heater, a good bimetal and a good evaporator thermistor (if equipped with one) and unit does not defrost on its own then you replace the adc board. If you have an evaporator thermistor then you would need to check the resistance at operating temps and compare them with factory specifications. The bimetal may have a letter and number on it indicating it's operating temps. Post number and letter and we can hopefully get you that info. Sounds like the door seals are good.

[Cubytus]

Good heater, bad bimetal (shut closed) for far.

Where would I typically find the evaporator thermistor, if the bimetal is on one side, half-height? I am asking because I can't leave a freezer half full of food with the door open while I'm pouring hot water over the coils to find out where this thermistor could be 

Wiring diagram shows two thermistors, but doesn't specify compartments. There's no telling where the other thermistor might be.

In case that may be helpful: I put three simple thermometers in the freezer: on the back plate, it shows -18C. Bottom door shelf: -8C, top door shelf: -10C. This was after a full night of keeping the freezer closed. Is such a wide gradient normal?

[16345Ed]

There isn't always one on the evap. Sometimes just one in freezer liner and one in fresh food liner. 

[Cubytus]

Liner means it is essentially inaccessible?

[16345Ed]

no usually a plastic grated cover pops off of them. 

 

Your diagram didnt include defrost circuit?

[Cubytus]

That is the complete diagram on the back of the fridge. I can identify the heater and its thermal fuse in series, part of the defrost circuit.

There's no other cover than the usual liner, and the coil metal plate of course.

[16345Ed]

I tried viewing parts diagram but its difficult, I saw what they called a thermostat box, and a defrost sensor. Both the thermostat and the sensor should be clipped to evaporator tubing somewhere. 

[Cubytus]

I have this blurry picture of the coil, before it was full of frost. On the right you can make out the thermal fuse in series with the heater, the heater on the bottom. On the top right side, below the metal plate bracket, one can make out a white cable where its extremity is covered by a black thermo tubing.

http://image.bayimg.com/9bbaac6a346c4e8799c7ae832e0e9c95afdef654.jpg

As for the thermostat box, its shape reminds me of this one (taken from a Kenmore, but otherwise remarkably similar in shape)

http://www.rcappliancepartsimages.com/dbImages/i/00002180/Air-Duct-C0507-4-1-1-00656587.jpg

Assuming we are looking at the same exploded view, part 21 should be the thermal cut-off I tested, and part 20 the sensor referred on the wiring diagram, and the black-clad device?

 

[johntech]

According to repai clinic this is your defrost sensor.Part number: C0817.4.7

[johntech]

I the white bulb on the end is the thermistor. If that is not reading the temp correctly then it will not defrost properly. I do not know Danbys thermistor resistance chart but maby somebody here will and chime in.

[Cubytus]

Looks like a dual sensor: white in the fridge, black in the freezer. Each has its own pair of wires.

Would that make sense?

also, Danby appears to be mostly rebranding models from other manufacturers, that may explain why the control board is also referenced under the Fridgidaire brand, and that some parts are also used in Kenmore.

I this is a faulty sensor, I do t know how I would access the harness as it must pass between the outer panel on the back of the fridge and the internal casing. This large piece of metal looks very hard to remove, and I assume I would have to break the insulating foam, at the very least, to access the wiring harness. I'll try to follow the wires.

[Cubytus]

I have a different picture for this on the same RepairClinic website, with the same reference:

Link

Yours looks correct, but I don't find it with the link you provided. Since AppliancePartsPro doesn't list Danby, which brand have you found it under?

Also: I manually defrosted the sensor clad in black tubing, leaving the heater plugged on a household timer. This morning, the fridge stopped for 45 min before restarting. Is it possible that the sensor wasn't sensing the right air temperature after it is pulled from the coils, and kept the fridge running?

In which case, should the board be to blame for not issuing "preventive" defrost to avoid the sensor freezing, or the sensor not correctly reading temperature?

[Cubytus]

An update on this:

i just changed the controller card on the 12th for a new one directly from Danby, and very quickly the coils started to freeze over again, impeding air flow.

FWIW, a completely dry coil (manual thaw) lets the fridge run for 20 min, shut down for 25. That is, after days of using very aggressive thawing, basically turning it on manually whenever the fridge shut down, for as long as it stayed off. This was of course very inefficient, but proves the compressor and gasket are doing their job properly.

After replacing the card and 4 days of frost build-up, it runs non-stop for more than an hour, but still shuts down for about 25 min before restarting. Logically, that would mean the fridge sensor is providing the correct information.

About the sensor, both our pictures are wrong: under aC0817.4.7, ApplianceParts shows one black and one white sensor connected to a 4-lead connector (same as sold by Danby parts department), RepairClinic shows one white "bulb" while the black lead goes to an intermediate 2-lead connector, and still goes to a 4-lead male connector.

However my DFF280WDB is different: the control card indeed has a 4-lead header, one pair providing around 12V for the fan, the other one linked to the freezer sensor through a 2-lead connector (still different than the one shown here). Danby confirmed they don't have any other part number for this fridge model.

This is very confusing, to say the least.

also, what would cause thawing failure now? 

I tested the freezer sensor while connected to the card, and got a reading of 3.39k ohms at -15C.

 

[Cubytus]

An update on this:

i just changed the controller card on the 12th for a new one directly from Danby, and very quickly the coils started to freeze over again, impeding air flow.

FWIW, a completely dry coil (manual thaw) lets the fridge run for 20 min, shut down for 25. That is, after days of using very aggressive thawing, basically turning it on manually whenever the fridge shut down, for as long as it stayed off. This was of course very inefficient, but proves the compressor and gasket are doing their job properly.

After replacing the card and 4 days of frost build-up, it runs non-stop for more than an hour, but still shuts down for about 25 min before restarting. Logically, that would mean the fridge sensor is providing the correct information.

About the sensor, both our pictures are wrong: under aC0817.4.7, ApplianceParts shows one black and one white sensor connected to a 4-lead connector (same as sold by Danby parts department), RepairClinic shows one white "bulb" while the black lead goes to an intermediate 2-lead connector, and still goes to a 4-lead male connector.

However my DFF280WDB is different: the control card indeed has a 4-lead header, one pair providing around 12V for the fan, the other one linked to the freezer sensor through a 2-lead connector (still different than the one shown here). Danby confirmed they don't have any other part number for this fridge model.

This is very confusing, to say the least.

also, what would cause thawing failure now? 

I tested the freezer sensor while connected to the card, and got a reading of 3.39k ohms at -15C.