Is this a bad circuit board? (fridge)

[wopachop]

Its the type that uses the resistance probe. Which is all fine and dandy. I have not measured the ohms but assume its measuring accurately.

Lets pretend the temp probe was hanging off the fins. Resistance to the circuit board is way out of spec so the fridge goes into a protective mode. Why the heck didnt it cycle all day? Man i just got home. Nothing i could do. Havnt opened it yet. I dont understand how it could go so long without attempting a cycle.

I have my probe attached to the fins. Its not hanging. Im just trying to present the topic as if the probe is set anywhere. Cut the thing in half with diagonal cutters. Can the fridge really go that long and not try to cycle? Makes me think maybe the circuit board is not working properly.

Its been overly hot. I left my front bedroom AC running. Which feeds cold air to the back of my fridge. I checked my phone this afternoon and saw the bedroom temp was 90F. Which meant the AC was not running. Got home and sure enough the dial AC was set to LOW. But it was not blowing cold air. That is another failure i need to figure out. Will ask if the shore power went out today.

[wopachop]

Found the answer!! Want to play along and try to guess?
To recap im used to seeing those spikes every couple hours. The air temp drops when the electric element turns on.

What confused me is that big curve in the middle. My first thought was that my circuit board might be failing, because it appeared to go 10 hours without the electric element turning on.

That was wrong. The graph below shows what really happened. Do ya see it?
Hint: the graph below shows more info than the graphs in post #1

[wopachop]

I cant seem to trick my circuit board into 24/7 operation. Its a dometic with the temp probe only. No dial controls. I can leave the probe dangling in the wind and the graph will look the same with spikes every couple hours indicating the cooling cycle starting and stopping.

With a dangling probe, i should see air temp get down to say 35ish and stay there? Because the electric heater is still turned on for constant cooling? THe graph would not show the normal spikes. It would be more rounded with temp rising very slightly according to ambient temps.

Reason i ask is for super hot days when im opening the fridge a lot. Would be nice to just pull the probe off and let it danger during the heat of the day.

[wopachop]

Nice info thanks. Its like a cooler in the sun versus in the shade.

[smthbros]

wopachop wrote:
Ok pretend the temp setting has the fins at 30F so the air temp will read roughly 40F.

If you dont touch those settings, and leave the fridge closed for days, why would you see a fridge air temp down at 35 or 36F? The heating element should have turned off back when fridge air temp was closer to 40F.

As your data indicates, the air temp in the fridge is variable. The fridge cycles to maintain a temp range at the evap fins. The air temp varies with heat gain thru the fridge cabinet wall. The heat gain into the fridge is a function of the temp difference between inside the fridge and outside the fridge, as well as the resistance to heat flow provided by the fridge cabinet.

[wopachop]

Ok pretend the temp setting has the fins at 30F so the air temp will read roughly 40F.

If you dont touch those settings, and leave the fridge closed for days, why would you see a fridge air temp down at 35 or 36F? The heating element should have turned off back when fridge air temp was closer to 40F.

[Old-Biscuit]

With the fridge doors closed for days at a time, and 3 fans blowing inside my fridge, why does the electric element turn off while the air temp inside the fridge is 40+ degrees?

Thermistor measures FIN temp which will be 10*F Lower then food compartment temps

Thermostat is calibrated for a temperature range based on TEMP SETTING

40*F inside fridge is 30*F FIN temp and temp has been reached/satisfied so no 'heat' (Cooling cycle) required

SO what temp setting are you using??

Is your food staying COLD.
(do you do this OCD testing with A/C Unit, Oven calibration, Water pump Discharge pressure/flow?

Simple..........

[wopachop]

I think i have a new question. Will often makes threads that are too long and confusing. (edit...it just happened again below. sorry)

Can we talk about how the cooling fins are getting colder? Which effects the air temp correct? I have a fan blowing directly onto the cooling fin where the temp probe attaches.

I want to believe the fridge will keep the electric element ignited and hot, until the temp probe gets cooled down to a certain level. I understand that the cooling fins will reach this low temperature before the entire fridge is cooled. But the part im confused about is below:

1. With the fridge doors closed for days at a time, and 3 fans blowing inside my fridge, why does the electric element turn off while the air temp inside the fridge is 40+ degrees? Remember doors are closed for days and lots of air circulation. 2 fans on the fins and 1 fan on the lower shelf blowing upward. I would expect my graph to show a more consistent lowest temp. I consider the probe a mechanical device. It works or its broken. While the circuit board can have a mind of its own. Terminator style. Im no stranger to circuit boards i will be soldering our home oven circuit board today. No joke will take a pic. The display died. A couple resistors are super hot and burned the board. Looks as if the solder joint is wiggling where it hits the board. I can tell a repair took place there because the solder looks chunky and different. It was a used board bought online a couple years ago. I think their repair came loose.

Hows that for confusing a thread?
I enjoy thinking. Its fun when you guys tell me im wrong. Not the first time and wont be the last. Thats how you learn is through making mistakes.

[wopachop]

Ok then lets forget the term "cycle". We can call it something else.

What do you call the cycle of the electric element turning on, heating the stuff inside the pipes, then turning off?

This happens many times a day. I would call that a cooling cycle but it seems to bother doug so lets call it something else?

[dougrainer]

wopachop wrote:
I think youre way off with #1 and #2 Doug. Thanks for helping though.

#1. The tstat runs in cycles, no? It cools until the probe reaches a resistance. Then the burning stops. Once the resistance rises to a certain level the burning starts again. Is that not a cooling cycle? Whatever you want to call it, that is the topic im hoping to discuss.

#2. I agree the air temp will vary slightly from food temp. But they are very close and in my experience you can measure air temp and get a good idea what the food temp is. To say "NOT AT ALL" is plain silly. Ive been gauging air temp right next to a bottle of water with a dial thermometer in it. Promise they are always very close. Enough to determine if your fridge is cooling properly or if youre running a bit warm come summertime.

1. There is NO CYCLE at all in any refer. The refer will run until the tstat is satisfied. If it take 6 hours or 24 hours the refer will run until the temp reaches set temp

What the hell do you think this says?????????? The refer will respond to what the Thermister tells the Circuit Board. Please respond, Are YOU an Engineer?

I appreciate your testing me. I just have 42 years as a TRAINED RV Tech. But to state air temp and water temp is a gauge of actual testing shows you have a lot to learn. Doug

[wopachop]

Nv Guy wrote:

wopachop wrote:
I think youre way off with #1 and #2 Doug. Thanks for helping though.

#1. The tstat runs in cycles, no? It cools until the probe reaches a resistance. Then the burning stops. Once the resistance rises to a certain level the burning starts again. Is that not a cooling cycle? Whatever you want to call it, that is the topic im hoping to discuss.

#2. I agree the air temp will vary slightly from food temp. But they are very close and in my experience you can measure air temp and get a good idea what the food temp is. To say "NOT AT ALL" is plain silly. Ive been gauging air temp right next to a bottle of water with a dial thermometer in it. Promise they are always very close. Enough to determine if your fridge is cooling properly or if youre running a bit warm come summertime.

Back when I was in the RV biz, if you called Dometic tech support and reported interior air temp rather than the temp from a container of water, they would all but hang up on you.
Air temp is unreliable - you need a thermal mass to determine actual accurate interior temp.
Why do you think the manufacturers attach the themistor to the refer fins (thermal mass) as opposed to just let it dangle in the wind?

The probe on the fins controlling temp is much different than an air temp thermometer telling you current air temp.

The fin temperature is controlling what the fridge does.
The air temp is just a basic understanding of what the current temp might be. Food temp will be lagging behind.

[Nv_Guy]

wopachop wrote:
I think youre way off with #1 and #2 Doug. Thanks for helping though.

#1. The tstat runs in cycles, no? It cools until the probe reaches a resistance. Then the burning stops. Once the resistance rises to a certain level the burning starts again. Is that not a cooling cycle? Whatever you want to call it, that is the topic im hoping to discuss.

#2. I agree the air temp will vary slightly from food temp. But they are very close and in my experience you can measure air temp and get a good idea what the food temp is. To say "NOT AT ALL" is plain silly. Ive been gauging air temp right next to a bottle of water with a dial thermometer in it. Promise they are always very close. Enough to determine if your fridge is cooling properly or if youre running a bit warm come summertime.

Back when I was in the RV biz, if you called Dometic tech support and reported interior air temp rather than the temp from a container of water, they would all but hang up on you.
Air temp is unreliable - you need a thermal mass to determine actual accurate interior temp.
Why do you think the manufacturers attach the themistor to the refer fins (thermal mass) as opposed to just let it dangle in the wind?

[wopachop]

I think youre way off with #1 and #2 Doug. Thanks for helping though.

#1. The tstat runs in cycles, no? It cools until the probe reaches a resistance. Then the burning stops. Once the resistance rises to a certain level the burning starts again. Is that not a cooling cycle? Whatever you want to call it, that is the topic im hoping to discuss.

#2. I agree the air temp will vary slightly from food temp. But they are very close and in my experience you can measure air temp and get a good idea what the food temp is. To say "NOT AT ALL" is plain silly. Ive been gauging air temp right next to a bottle of water with a dial thermometer in it. Promise they are always very close. Enough to determine if your fridge is cooling properly or if youre running a bit warm come summertime.

[dougrainer]

1. There is NO CYCLE at all in any refer. The refer will run until the tstat is satisfied. If it take 6 hours or 24 hours the refer will run until the temp reaches set temp
2. You CANNOT gauge Air temp in a RV refer for testing. NOT AT ALL.
3. What I use is a USB Temp Logger in a glass of water set in 15 minute increments. While the Logger starts out at a warm refer after 24 hours the refer has reached its MAX cold. I leave the Logger in for 4 to 7 days depending on the customers complaint. When I remove it I can then down load the temp parameters to a spreadsheet and hand it to the customer.
4. The Temp Thermisters in both Norcold and Dometic sense the Metal fin temp. Fin Temp will be 10 degrees COLDER than the interior items in the refer-------you measure 25 degree fin temp then the interior items of the refer will be 35 degrees. Doug

[wopachop]

I think he is just talking about how quickly air temp can fluctuate inside the fridge. But that doesnt accurately represent the food temp. Would guess the denser and more massive the food, the longer it holds its temp. Like a giant body of water.