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kymooses View Drop Down
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Posts: 1807 		Direct Link To This Post Topic: Bypass Fridge T-stat control
    Posted: 01 Sep 2011 at 10:42am
For those that have the dometic rm 8501 fridge with the two t-stat controlled auxillary fans in the back.  Has anyone bypassed the t-stat completely and simply put them to run all the time or on a switch?
 
I'm still not sure my fans have ever worked.  I suppose the t-stat switch could be bad.  But I've had a hard time explaining it to my dealer.  Because they don't always run they kinda said just keep an eye on it. 
 
I'm buying a thermometer for my fridge today to check and see what temps it reaches and if it can't get to certain temps I'll have some proof to show them so they'll check the fridge out for me more.
 
I'm just not sure how I should proceed at this point.  I don't think it's cooling like it should and still don't think the fans have ever worked to help remove the excess heat from the compartment.
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Posts: 9062 		Direct Link To This Post Posted: 01 Sep 2011 at 12:36pm
Should be a very simple procedure if you decide to do it, just find the 12 volt input to the fridge and tap into it, cutting the wires going to the fans and extending the wires to the source.  There are some downsides to this.  At full speed they are noticeable.  I won't say loud, but if you are laying in bed at night when its quiet you will definitely hear them.  Second, while running them all the time when you are plugged in isn't a big problem, if you do this while boondocking you'll drain your battery much more quickly.  Adding two switches - one for each fan - would give you some control over when and how much they blow.  Or if you know how to size a potentiometer for the load, you could add one to give you an adjustable range (using one to power both fans, no reason for two).
 
Another solution would be to find two 12 volt thermostats, one which is pre-set to trigger around 80 F, or can be set to that temperature.  Another which triggers around 100 F for the other fan.  These numbers are guesstimates and you may do better calling FR or Dometic to find out what temperatures trigger low/medium/high with the existing thermostat control.  Which leads to a downside of this solution, unless you find one that can ramp up the fan over a temperature range (like the fridge does), you'll only have all-or-none control.  Which may lead to a constant on-off-on-off cycle.  Better than nothing at all, but not perfect.
 
Before doing any of this, try opening the top vent, put it in a plastic grocery bag, and put the vent back in place.  This should trigger the fans even on a relatively cool day.  If not, open the bottom vent and blow hot air into the compartment with a small heater on low.  If THAT doesn't do it, you have definite proof of a problem and should demand a fix!
 
I asked my dealer to do the plastic bag thing just a few weeks ago, because my fridge was cycling a relay constantly somewhere on the control board, when it was in 120 volt mode ONLY when the fans were on.  Sure enough, no matter how much he tried he couldn't get it to happen even though I had heard it numerous times... Angry
Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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ka9nyn View Drop Down
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Posts: 8 		Direct Link To This Post Posted: 01 Sep 2011 at 12:53pm
If you want to run them continuously, try rewiring them in series & connecting
direct to the 12 VDC supply.
The fan speed drops and so does the noise.
I've wired fans like this for some of my ham radio
projects.
 
Dave & Rose
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kymooses View Drop Down
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Posts: 1807 		Direct Link To This Post Posted: 01 Sep 2011 at 3:18pm
Got mine to kick on finally, fiddling with all the connections it seems one of them leading to the t-stat was loose.
 
They do only seem to kick on for a very short time though to evacuate some of the hot air.  I still might put them on a switch.
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Posts: 571 		Direct Link To This Post Posted: 01 Sep 2011 at 5:24pm
Ky, we found that the fans were running in our 171, but we still had 50 degrees in the frig. We got one of those little battery operated fans that seems to move no air, and found the temp dropped to the low 30's and ice stayed frozen in the freezer. A cold mass also helps to maintain temp, like a six pack of cans of soda or adult beverage. We precool with shore power and run on the battery pack when trailering.
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Hodge-PODge View Drop Down
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Posts: 539 		Direct Link To This Post Posted: 01 Sep 2011 at 9:26pm
I have a battery operated fridge fan and a thermometer.  I have my thermostat set as cold as it will go but I cannot get my fridge any colder than 38 degrees.  If the door gets opened too many times, it will go up to about 40.  I hope that is cold enough for deli meat and bacon!
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Direct Link To This Post Posted: 02 Sep 2011 at 4:32am
http://www.ehow.com/facts_4896679_what-safe-temperature-refrigerator.html
 
40F is close to the upper limit.......how accurate is your thermometer??????
 
 
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Posts: 539 		Direct Link To This Post Posted: 02 Sep 2011 at 7:15am
That's my concern - the temp is at the UPPER limit, and I think the thermometer is accurate.  This morning it looked like it had cooled to about 36 degrees.  I think part of the problem is the ambient temperature.  It's been running in the mid to upper 90's here all summer.
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Direct Link To This Post Posted: 02 Sep 2011 at 11:04am
Originally posted by Hodge-PODge

That's my concern - the temp is at the UPPER limit, and I think the thermometer is accurate.  This morning it looked like it had cooled to about 36 degrees.  I think part of the problem is the ambient temperature.  It's been running in the mid to upper 90's here all summer.
 
I understand your concern, as I would be too.  Also, I agree that the ambient temperature doesn't help matters.  As you probably already know, a fridge just transfers heat from one place (inside the fridge) to another (behind the fridge).  The closer the temperature differential between the ambient temperature and the coils/fins (that are trying to get rid of heat) the less efficient it works.  It would be interesting to put a temperature probe in the cavity behind the fridge and see just how warm it is. 
 
The "stock" fans are nice but, if memory serves, they are not ducted in any way.....they just blow around the hot air in the cavity.
 
If it is any consolation....it is supposed to get to 101F today in Indy.  I'm going camping anyway!
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kymooses View Drop Down
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Posts: 1807 		Direct Link To This Post Posted: 02 Sep 2011 at 11:20am
Originally posted by David

 
If it is any consolation....it is supposed to get to 101F today in Indy.  I'm going camping anyway!
 
 
I know David, we just got our Louisville weather alert saying it'll be triple digits early this afternoon and climbing into the mid evening.  Ugh, I still have to get home, hitch up the pod, pack most of everything and get firewood loaded.
 
Not the "happiest camper" right now, but still a fairly happy one.  Happier once camp is set up tonight that's for sure!
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