How important is a refer thermistor?

[hotjag1]

I have read on this forum that the thermistor is critical to proper refer temps because it controls the cooling cycle. Our refer starting running about 10 degrees warmer than usual(44 degrees) in 80 degree temps. I adjusted the thermistor up and down at different intervals and the temps didn't change.

After adjusting the thermistor several time the plastic clip broke off, so I just laid the broken piece with the attached wire on the shelf. After a couple of hours the refer temp went down to 37 degrees and this morning it was at 33 degrees. I changed the setting on the front of the refer down one notch and the refer stayed at about 37 degrees. So why do I need to replace the thermistor if it seems to maintain a decent temp using the front control button? It is a double door Dometic.

[enblethen]

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[hotjag1]

Chris Bryant wrote:

hotjag1 wrote:
. I am going to try and locate a thermistor on Monday.

Again, the clip does not come with a new thermistor, they are separate parts with separate part numbers.

Good to know. Hopefully the parts store will know that too.

[Chris_Bryant]

hotjag1 wrote:
. I am going to try and locate a thermistor on Monday.

Again, the clip does not come with a new thermistor, they are separate parts with separate part numbers.

[hotjag1]

BruceBrown, Our cooling unit is only a few years old too. Yours could possibly be the thermistor because with ours it is staying very cold with an unattached thermistor. Outside temp was 82 degrees and refer stayed at 35 degrees.

wa8yxm, you are correct about continuous cooling as the refer was at 30 degrees this morning. I am going to try and locate a thermistor on Monday.

[wa8yxm]

PastorCharlie wrote:
As long as it works proper do not fix it.

The thermistor itself is vital without it the control system has no clue as to how hot or cold it is in there so it will either keep cooling till everything is froze solid... or shut down and nothing gets cold..

However as the Pastor said. If its working.. Don't fix it. You might want to "Attach" it to the current location somehow.. I suggest a glue on "eye" with a zip tie to hold it. (nothing that cuts or covers) or a peal and stick eye (like you'd stick the zip tie through) and stick the sensor into the eye if it's the right size. Just as long as you do not tear it out removing the shelf.

[Bruce_Brown]

Chris Bryant wrote:
The plastic clip is separate from the thermistor.

I believe he is speaking of the plastic clip that holds the thermister in place.

As to the original subject, this is good timing. Last season our fridge started doing the same as the OPs. The cooling unit isn't very old so I was surprised. The fans seem to be working, but even with that I put in a temporary fan to assist - the result was no change.

As our season is about to begin I have started thinking it might be time for a new residential fridge. I'd rather not go this route if I don't have to but I'm not buying a new cooling unit for this one either.

We head out for our first trip next week, I'll keep this thread in mind.

[Chris_Bryant]

The plastic clip is separate from the thermistor.

[hotjag1]

Ralph Cramden...I've always had really good luck with this fridge as it consistently maintains temps in the mid 30's until the outside temps are in the high 80's to 90, then the fridge temp will rise to 40. It has been around 80 to 82 for several days in AZ and the fridge stayed in the 30's until yesterday. It then moved up to 44 and then 46.

The thermistor clip has been cracked for quite awhile and then broke completely off when I was adjusting it. With no thermistor attached the refer is staying around 34 to 36 when the outside temp is 80 degrees so it appears that Tiffin installed it correctly and the fans are doing their job properly. Knock on wood:)

[ppine]

Important to control the temp.

[dougrainer]

Scottiemom wrote:
I believe the thermistor is important to defrosting the fridge. When ours was not working, the fridge was still cold, but the fins would build up with ice and couldn't melt. It also caused water droplets to build up on the roof of the case and things would be wet when we were in/out of it while fixing a meal. It was a quick easy fix to install a new one that DH did himself.

Dale

RV refers have NO defrost cycle at all. All RV refers do is cool the items. Frost/ice build up you must manually defrost them. IF you have excessive ICE on the evap fins, that will degrade the cooling capacity as ICE is a great insulator for cooling capacity. A thin film of ice is normal and will not degrade cooling. Doug

[Ralph_Cramden]

hotjag1 wrote:
I have read on this forum that the thermistor is critical to proper refer temps because it controls the cooling cycle. Our refer starting running about 10 degrees warmer than usual(44 degrees) in 80 degree temps. I adjusted the thermistor up and down at different intervals and the temps didn't change.

Is the fridge 10 degrees warmer than it was before when the ambient temperature was 80? or 10 degrees warmer than when the ambient temperature was 70?

An absorption fridges ultimate cooling ability is related, although not directly related in terms of a degree cooling for every degree ambient, to the ambient temperature. Once the ambient is above 80, even more so if the sun is on the side of the rig with the fridge, the fridge starts getting incapable of supporting those interior temps in the 30's no matter the thermistor position, brand, age, or anything else.

Add to that the RV manufacturers are notorious for building the compartment wrong instead of following the fridge manufacturers guidelines, so they don't naturally draft enough. That or they jam them in a slide with no ability to use a roof vent.

Adding 12 volt fans to vent the space is the cheapest and best mod one can make to any absorbtion fridge. If you have a Dometic with the OEM fan, it's a noisy POS anyway or it will be given time. If you add some good fans you can kill the OEM one.

[Scottiemom]

I believe the thermistor is important to defrosting the fridge. When ours was not working, the fridge was still cold, but the fins would build up with ice and couldn't melt. It also caused water droplets to build up on the roof of the case and things would be wet when we were in/out of it while fixing a meal. It was a quick easy fix to install a new one that DH did himself.

Dale

[hotjag1]

Thanks Old Biscuit... that is a great explanation as to how the thermistor works in relation to the functions of an rv fridge. I will replace the thermistor as it is a very inexpensive part and I want the refer to operate as originally designed. If it was something that might cost several hundred dollars, I might think otherwise(jury-rig) since the refer could be used and kept cool as you state.

Thank-you for the in-depth explanation. BTW, you add a lot of very good information to this forum on many subjects!

[Old-Biscuit]

Thermistor is the temp sensing probe that the thermostat uses to control cooling cycles (turn heat source on/off)

Thermistor senses the FIN temp and the thermostat is calibrated for the thermistors location on the OEM FIN

Adjusting the thermistor UP/DOWN is a minor temp adjustment for 'AUTO TEMP CONTROL' fridges..those that do NOT have adjustable temp settings.
Temp range is 6*-8*F overall

With thermistor NOT attached to the far right fin (OEM position) the thermostat does not have feedback on FIN temp therefore it allows continuous cooling cycle.......and is now functioning in 'limp mode'

Unplugging the thermistor from lower circuit board will have same affect


Moving 'temp setting' will have minimal affect overall.......fridge heat sources will run/operate MORE then necessary to properly cool fridge.

No need to run fridge longer then necessary.

Snip-The-Tip ....thermistor replacement w/o having to pull old leads out/run new leads ....replaces the thermistor probe with a 'rheostat' control that attaches to side wall of food compartment


OR NOT.........it's your fridge and you can do as you please.
Folks 'jury-rig' stuff all the time.