Every year I read a lot of posts about clogged cooling unit tubes. Every year when my 18 year old Norcold 682IM is above 40 degrees in the refer compartment I wonder if it is getting clogged. It was 90 degrees the other day and I was shooting the tubes and boiler in the back with my HF IR temp gun looking for cold spots, thinking that this would be a blocked section. Is this a way to check for blocked sections of tubing? I don't know what temps the tubes or boiler section should be at for optimal cooling. Also I was thinking if you knew what the optimal temps should be at for various sections of the refer cooling unit I would think that by taking temperature readings at certain reference points this would be a better way to level the unit assuming that the lowest temp is the best condition, and once you find the lowest reading then set a bubble leveler inside the MH to match this lowest temperature reading. Any thoughts?

If the tubes are blocked it is a permanent condition and leveling is too late.Good Luck, Mike

Some have had success by turning the refer upside dowm for several hours, which may free the blockage. Its worth a try.

harold1946 wrote:Some have had success by turning the refer upside dowm for several hours, which may free the blockage. Its worth a try.X2I was referring to permanent as reguards to leveling not helping as this condition is caused by operating out of level.

You can check for a blockage by feeling the coolant tubing when the fridge is on. The tubing should be warm to hot. If the tubing suddenly turns cold your blockage is at that point. You can try taping that point "gently" with a piece of wood. This often works. As someone else mention you can also remove the fridge and tune it upside down for a day or two but that is a lot of work. Try lightly taping as I mention above first.Use the diagram below to see what areas should be cool and hot. The coolant cools as it flows back to the absorber tank.Good luck and repost on your progress. -Tom, W3TLN

popeyemth wrote:harold1946 wrote:Some have had success by turning the refer upside dowm for several hours, which may free the blockage. Its worth a try.X2I was referring to permanent as reguards to leveling not helping as this condition is caused by operating out of level.An "out of level" condition normally does not cause a blockage. A blockage is mostly caused by inadequate airflow. A blockage can be cured by turning upside down as someone mentioned above. There is no greater "out of level" condition that turning the fridge "upside down". -Tom, W3TLN

How to check a refer cooling unit for blockage | Good Sam Community

18 Replies

Gjac
Explorer III
Jul 15, 2014
Chris Bryant wrote:
The best solution to this problem- something the OEM's *should* put in, IMHO, is the ARP refrigerator control, which monitors boiler temperature and reacts quickly to prevent overheating. You will find a bunch of data on that site about the issue.

There are 2 other issues internal to a cooling unit- the Hydrogen can leak out over time (a long time though), due to slightly porous welds (and Hydrogen is a small molecule), and when the sodium chromate overheats, it releases nitrogen. The nitrogen will fill up the lower part of the unit, and is often the cause of cold freezer/warm refrigerator, as the nitrogen displaces the hydrogen in the fresh food compartment.
I looked at the ARP web site. This would seem to answer the second question I had if I understand it correctly. What I was trying to figure out is with a simple HF IR gun which many on here have could we shoot the same spot on the flue where it looks like the ARP temp sensor is installed and develop a tolerance for of level? Sort of a manual ARP system? I think the answer is yes. Although the ARP not only records the temps but shuts it down when it gets too hot.
sjholt
Explorer
Jul 15, 2014
In my 19 year old Norcold 683, all I get when the weather is over 90 degrees is 5 degrees in freezer and 40 degrees in the fridge with the setting on 5 or max.
If it cools down outside overnight then in the morning the temps will get down to
2 and 36 on max. I think your unit is working normally for an old Norcold. when the temps run 80-85 during the day and cools down to 60 at night, the temps run 0 and 35 with the setting on 3.5.
Over 40 years and three different vehicles, the temps run about the same.
Chris_Bryant
Explorer II
Jul 15, 2014
The best solution to this problem- something the OEM's *should* put in, IMHO, is the ARP refrigerator control, which monitors boiler temperature and reacts quickly to prevent overheating. You will find a bunch of data on that site about the issue.

There are 2 other issues internal to a cooling unit- the Hydrogen can leak out over time (a long time though), due to slightly porous welds (and Hydrogen is a small molecule), and when the sodium chromate overheats, it releases nitrogen. The nitrogen will fill up the lower part of the unit, and is often the cause of cold freezer/warm refrigerator, as the nitrogen displaces the hydrogen in the fresh food compartment.
dougrainer
Nomad
Jul 15, 2014
The temp measurement will be at the burner flue as that is the area that heats up(overheats) when you have a partial or blocked cooling unit. The normal temp of a Norcold 1200(dual 120 elements at 450 watts total is around 350 degrees. SO, a Dometic 2 door or Norcold 2 door uses a 325 watt element, so I will guess that temp in the 325 degree range. The Norcold recall box is set to trip at over 700 degrees. So, you have a variable of over 350 degrees before the recall trips. Doug
Gjac
Explorer III
Jul 14, 2014
dougrainer wrote:
Gjac wrote:
I understand that this blockage is a slow build up over time and understand how to check to see if the refer is totally blocked. What I was trying to figure out is if temperature measurement could alert us if the cooling unit is starting to have blockage. I would think the blocked areas would be cooler than the rest of the tubing. I check my radiator this way to look for blockage and it shows cold where radiator starts to develop blockage.

Yes, you can use a temp measurement, but it has been so long, I do not have the variables or temp normal measurements. It is just as easy to do the 120 element hot wire test. IMO, all cooling units will have a small blockage over the years due to the occasional running off level. NOBODY, always runs the refer within spec all the time. Doug
Thanks for the further understanding Doug. I'm not sure anyone understood my second question but would also appreciate any incite you have. You and Chris and others have posted many times about refers running hotter when off level so my thought was if you can establish a ref point maybe several inches above the flue and take some temp readings over time and various out of level angles I would think that at the lowest temp reading this would be the best condition, as you move off this condition and the temps begin to rise this would be the acceptable out of level tolerance that the refer can safely operate at. Do you know if the refer Mfg's have done something like this to establish the out of level tolerance.
dougrainer
Nomad
Jul 14, 2014
Gjac wrote:
I understand that this blockage is a slow build up over time and understand how to check to see if the refer is totally blocked. What I was trying to figure out is if temperature measurement could alert us if the cooling unit is starting to have blockage. I would think the blocked areas would be cooler than the rest of the tubing. I check my radiator this way to look for blockage and it shows cold where radiator starts to develop blockage.

Yes, you can use a temp measurement, but it has been so long, I do not have the variables or temp normal measurements. It is just as easy to do the 120 element hot wire test. IMO, all cooling units will have a small blockage over the years due to the occasional running off level. NOBODY, always runs the refer within spec all the time. Doug
Gjac
Explorer III
Jul 14, 2014
I understand that this blockage is a slow build up over time and understand how to check to see if the refer is totally blocked. What I was trying to figure out is if temperature measurement could alert us if the cooling unit is starting to have blockage. I would think the blocked areas would be cooler than the rest of the tubing. I check my radiator this way to look for blockage and it shows cold where radiator starts to develop blockage.
dougrainer
Nomad
Jul 13, 2014
The ONLY way to verify cooling operation is to wire the 120 element direct for 24 hours and make sure all rear ventilation is open and clear and IF installed the rear fan/s are running. IF you do NOT get below 10 degrees in the freezer and 36 to 40 in the refer, your cooling unit is defective. makes no difference if block or a slight leaker. The CAUSE of a blocked cooling unit is---RUNNING OFF LEVEL. The blockage is "welded" to the inside of an upper tube and CANNOT be fixed by burping(turning the refer upside down). Burping will restore some cooling, but as the Ammonia gets blocked again you lose all cooling. Burping does NOT restore the complete COLD operation but will cool, but usually not below 40 to 45 degrees until the Ammonia blocks up again. Blocked Ventilation will "COOK" a cooling unit in less than 24 hours and render it completely inoperable. This is different from the standard blockage. Doug
Old-Biscuit
Explorer III
Jul 13, 2014
popeyemth wrote:
It's my understanding that operating out of level causes inadequate airflow .

NO.......

Operating out of level interrupts the proper gravity flow of the coolant inside the tubes.
When the flow is interrupted overheating can occur. When overheating occurs the rust inhibitor in the coolant crystallizes and and begins plating out on the inside of the tubes......like plaque in an artery.
When it plates out it disrupts the proper gravity flow which causes overheating..more plating..more etc. etc.
This plating out is permanent, unrepairable (turning up side down/banging on the tubing is a band aid fix that doesn't 'fix' anything)....damage is accumulative until cooling dies.

AS for measuring temps....
Way to many variables.
Airflow, ambient air temp, humidity level, freezer temp, food section temp, flue temp, flue cleanliness, heat transfer etc. etc.
marcsbigfoot20b
Explorer
Jul 13, 2014
I had the problem.

I replaced the cooling unit as turning upside down is already half the job anyhow.

The New Amish cooling unit so outperforms the stock one, it isn't even funny.