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jmck1737 · 05-30-2018, 07:32 AM

I researched and spent hours searching and reading what I could about the issues with RV fridge cooling, especially Dometic, as that is what we have. Ours in in the slide on our 2008 Georgetown and has the upper and lower vents for cooling. I beleive the previous owner also had some problems with cooling as they had a small fan in the lower compartment which I replaced as outlined below. Below is what I have completed to date as far as upgrades to help with cooling.

I have installed 3 new computer brush less fans in bottom of the upper compartment to move air. These are rated at 74 CFM each. On the bottom I have installed an electric fan that moves significant air and is a 3 speed. I can feel air exiting the upper vent with the upper fans only on and more air with both upper and lower fans on.

I am still battling the issue of taking a long time to cool the refrigerator section and having it get to and stay at 34 -37 degrees. if we open the door the temperature will shoot up and take hours to get back down if it does. The freezer works great and will get it down to 0 degrees within 24 hours of startup.

So now to the questions and proposed solutions that I have not found definitive answers to and would like your experiences and advice on which direction we go.

Install another computer fan in the refrigerator section to move air. Was looking at 80mm fan that moves about 34cfm as this is a small area. Not an expensive solution if it doesn't help.

Snip the tip termistor upgrade. More expensive and have seen mixed reviews on line. Some say that it will not give more range than the current termistor.

Of course the ultimate solution would be to go with a residential or new cooling unit and have looked at these solutions. The Amish cooling unit is expensive and a major project and is supposed to be a better unit but still works the same as my current RV fridge. We have the smaller single door Dometic so are limited to a small size residential unit which from my research is hard to find and fit correctly.

Another question I had is can I blow too much air over the coils with my current fan setup thus overcooling the unit?

Any help from those of you who have battled this demon and won would be appreciated. I have enclose a photo of the fridge in the unit if that helps.

YC1 · 05-30-2018, 07:55 AM

I just love typing out a nice long response and then it goes away.

Check your vent tube/s. If they are cracked this will cause the issue. Be sure they have not been modified or a end lug removed if designed that way.

NHRA225 · 05-30-2018, 08:14 AM

If you google rv refer vent fans you'll find a variety of proposed solutions, at least I did. After all of the reading I Installed 3 x 85 cfm brushless fans in the upper exit of my roof vent. I turn them on when outside temps reach 80 degrees and upward and leave them on All of the time 24/7- Freezer is @ 0 deg and Fridge is 32 deg with my T stat set on 1/2 to 3/4 of a turn up. Now my disclaimer ! All circumstances vary- Temp inside you MH-- Sun Direction on the side of your Coach Ect.
When mine is not in use at anytime during the summer- My A/C is on keeping the inside @ 72 to 74 deg - This significantly helps the Refer keep cool.

Skip426 · 05-30-2018, 08:27 AM

It may be time to check the clearance , between the back of the fridge ( cooling unit ) and the wall of the RV.
Too much clearance will allow air to go up between the vents , without going across the cooling unit's fins.
Some manufacturers only installed a baffle at the bottom vent , but the max clearance of 1" should be maintained , most of the way up the vent cavity.

jmck1737 · 05-30-2018, 10:09 AM

Quote:

Originally Posted by YC1

I just love typing out a nice long response and then it goes away.

Check your vent tube/s. If they are cracked this will cause the issue. Be sure they have not been modified or a end lug removed if designed that way.

Thanks for the responses. I went back out and looked and did not see any cracks. No large amount of yellow powder either. Just turned it to Gas only to see if that would help. Electric got it down to 49 degrees running over night with temps in the low 70's but high humidity. AC on in the coach around 76 degrees.

YC1 · 05-31-2018, 08:18 AM

Pull the top vent out of the side and look down to perhaps find a couple of fans installed there. Use your phone to take pictures or a mirror.

If you find a fan or two and they are not running you need to chase the wires to the device that turns them on and off. It might have tabs on it and could be clamped to the cooling unit some place. Finding that device check to see if it has 12 volts on each side. If not, just jump across it and the fans should run if not defective.

If the fans are defective you can get to them by pulling the refer out several inches versus pulling it all the way out. That can be a trick finding hidden screws covered in dust in the back.

If you find the fans are bad be sure to install new vent tubing at the same time. The stuff they install becomes very brittle.

Old-Biscuit · 05-31-2018, 12:44 PM

OP Stated:
I am still battling the issue of taking a long time to cool the refrigerator section and having it get to and stay at 34 -37 degrees. if we open the door the temperature will shoot up and take hours to get back down if it does.

The freezer works great and will get it down to 0 degrees within 24 hours of startup.

Classic example of obstruction/blockage in cooling unit between LOW temp evap (freezer) and HIGH temp evap (food compartment)
Hot ammonia vapor is being condensed into cool Liquid ammonia in Condenser section (finned section at top of fridge).
That requires sufficient airflow/draft....which you have

The condensed liquid ammonia gets very cold when it mixes with the hydrogen gas.......it then absorbs heat from freezer via the LOW temp evap.

Then is has to absorb heat from food compartment (HIGH temp evap)
Until freezer section gets down to 10*F or lower the cold liquid ammonia can not absorb much heat from food compartment due to all the heat it had to absorb from freezer.
Your freezer is getting very cold (good) but food compartment temps take long time to cool down/recover .....

To test if 'cooling unit' is problem or if thermistor is you need to force cool the fridge
Unplug the thermistor leads from P2 connector on lower circuit board
Run fridge on electric for at least 12 hrs. W/O thermistor the fridge will 'cool' continuously (not turn electric elements off)
Temp in food compartment should get very cold ---possibly even freeze items

If it does.......replace thermistor (Snip-The-Tip is a convenient way but not a clue all)

If it doesn't then cooling unit has blockage which will only gets worst over time

jmck1737 · 05-31-2018, 02:08 PM

Quote:

Originally Posted by Old-Biscuit

OP Stated:
I am still battling the issue of taking a long time to cool the refrigerator section and having it get to and stay at 34 -37 degrees. if we open the door the temperature will shoot up and take hours to get back down if it does.

The freezer works great and will get it down to 0 degrees within 24 hours of startup.

Classic example of obstruction/blockage in cooling unit between LOW temp evap (freezer) and HIGH temp evap (food compartment)
Hot ammonia vapor is being condensed into cool Liquid ammonia in Condenser section (finned section at top of fridge).
That requires sufficient airflow/draft....which you have

The condensed liquid ammonia gets very cold when it mixes with the hydrogen gas.......it then absorbs heat from freezer via the LOW temp evap.

Then is has to absorb heat from food compartment (HIGH temp evap)
Until freezer section gets down to 10*F or lower the cold liquid ammonia can not absorb much heat from food compartment due to all the heat it had to absorb from freezer.
Your freezer is getting very cold (good) but food compartment temps take long time to cool down/recover .....

To test if 'cooling unit' is problem or if thermistor is you need to force cool the fridge
Unplug the thermistor leads from P2 connector on lower circuit board
Run fridge on electric for at least 12 hrs. W/O thermistor the fridge will 'cool' continuously (not turn electric elements off)
Temp in food compartment should get very cold ---possibly even freeze items

If it does.......replace thermistor (Snip-The-Tip is a convenient way but not a clue all)

If it doesn't then cooling unit has blockage which will only gets worst over time

Old Biscuit,

That is excellent info and I appreciate it. I definitely learned something. I will do that and test the thermistor. I had no idea how to test the unit other than what I have already done with voltage, fire, etc.

If it passes I would assume the blockage issue means new cooling unit or would the burp test (taking unit out and rolling it upside down and back a few times) I have seen on the web a possibility? I ran over night last night and only got down to around 43 degrees. We have a camping trip planned for this weekend so I may use that as a test.

jmck1737 · 05-31-2018, 02:12 PM

Quote:

Originally Posted by YC1

Pull the top vent out of the side and look down to perhaps find a couple of fans installed there. Use your phone to take pictures or a mirror.

If you find the fans are bad be sure to install new vent tubing at the same time. The stuff they install becomes very brittle.

YC1

Thanks for the replay and info. I have already changed the 2 DC fans I had in the top to 2 DC fans that moved almost twice the air as the old ones. I also have a fan in the bottom blowing up onto the coils.

I think Old Biscuit may have provided my next logical step. I am learning a lot about evaporative refrigeration whether I wanted to or not.

Old-Biscuit · 05-31-2018, 03:06 PM

Quote:

Originally Posted by jmck1737

Old Biscuit,

That is excellent info and I appreciate it. I definitely learned something. I will do that and test the thermistor. I had no idea how to test the unit other than what I have already done with voltage, fire, etc.

If it passes I would assume the blockage issue means new cooling unit or would the burp test (taking unit out and rolling it upside down and back a few times) I have seen on the web a possibility? I ran over night last night and only got down to around 43 degrees. We have a camping trip planned for this weekend so I may use that as a test.

Burping/flip-flopping fridge is a band-aid attempt at best

The sodium chromate in the cooling solution (anti-rust inhibitor) crystallizes from being overheated.......lack of coolant flow/off level operation, inadequate airflow/draft etc.
The crystals plate out on inside of tubing 9section between the two evap coolers) or in perk tube (boiler section)
The plating out is permanent....crystals will not go back into solution.

Burping/flipping etc might dislodge some of the crystals but they will just cause an obstruction elsewhere.

Force cool and determine if cooling unit or thermistor.

jmck1737 · 05-31-2018, 03:30 PM

Ok. couldn't wait to try Old Biscuits thermisor test. So out to the MH, shut down AC and DC power, unhook the P2 connector, power back on, and frig running on AC power. We shall see in the morning if this works and my fingers are crossed as the snip a tip is a much easier and less expensive fix.

jmck1737 · 05-31-2018, 03:32 PM

Quote:

Originally Posted by Old-Biscuit

Burping/flip-flopping fridge is a band-aid attempt at best
Burping/flipping etc might dislodge some of the crystals but they will just cause an obstruction elsewhere.

Force cool and determine if cooling unit or thermistor.

Thanks for the helpful info. Doing the thermistor test now so should know something tomorrow morning. will post results.

AbdRahim · 05-31-2018, 04:08 PM

Dealer told me the best these do is 38*F or so. Today was a cool day. This morning it was 34*. Now 37* - opened it a few times to prepare dinner.

jmck1737 · 06-01-2018, 04:14 AM

I guess I did not get lucky with the problem being the easier to repair thermistor. Went out to check and it was 50 degrees in fridge and 13 in freezer after running 12 hours with thermistor disconnected. Guess I order a cooling unit today. I could live with 34-38 degrees but not 40's and 50.