2004 MB fridge not performing well on propane while driving

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2004 MB fridge not performing well on propane while driving

April 28, 2021, 02:05:24 pm

I have been puzzled by the poor performance of the Dometic fridge while on long trips. Many years ago I installed a wireless thermometer sensor inside the fridge chamber to monitor the cooling performance. When the LD is stationary, the fridge temperature range is 32 to 36 F with either electric or propane which is in the normal range. However, the fridge does not cool when the LD is in motion on propane, the fridge temperature can rise to 48 F after a 5 to 6 hour trip! I checked the flame and it seemed to operate fine and accumulate tank appeared warm. There is no leak. The fridge has been this way since we bought it in 2011. In 2014, I put in a 600W solar system with a 440ah LiFePO4 battery pack so I use an inverter during sunny days we are on road and the fridge works well! This puzzled me even more. I installed another remote thermometer in the backside heater to check the performance of the propane burner after cleaning it. The outside temperature of the heater chamber appeared the same with either electric or propane operation, both at about 158F, but the darn propane mode just refuse to cool the fridge! Anyone with an insight on this strange behavior. BTW, both remote thermometers are mounted on the instrument panel so I can see the temperatures while driving and they and their performance are night and day.

Re: 2004 MB fridge not performing well on propane while driving

Reply #1 – April 28, 2021, 02:19:27 pm

'Frig warming up on the road

It’s suspected to be related to how air flows over the fridge vent while driving. See the link above for more. Muffin fans in the vent stack fixed the problem for me.

Rich

Re: 2004 MB fridge not performing well on propane while driving

Reply #2 – April 28, 2021, 02:30:10 pm

I’ll start with the simple things you likely already checked.
Is there enough room for the fridge to have good air circulation? The warm air goes up and the cold air goes down due to relative density. There are no stock fans to push the air around.
Has the sensor that sits on the fins moved down over the years? The holder on my fridge cracked. When I got a new one I was amazed how much cooler it stayed. Turns out when loading I accidentally moved the sensor.
Are you driving or facing west for most of the day? Sun beating on the compartment could be an issue for an older fridge. When in camp try to get that side away from the direct sun. If that is not possible consider getting a couple large blue ice (Igloo or some such brand) things used in ice cooler. Keep one in the freezer and the other in the refrigerator. Swap as needed.
John

Re: 2004 MB fridge not performing well on propane while driving

Reply #3 – April 28, 2021, 03:30:00 pm

To diagnose the issue, I would try to duplicate the driving conditions that might cause the issue. Start by placing a fan outside the fridge outside access door, blowing from front to back, and check temps over a few hours. If that is not the issue, it may be the airflow past the roof vent, so try the test up there. if that test is also negative, you will need 2 fans for the logical next step. Then, if airflow appears to NOT be the issue, a voltmeter monitoring the 12V to the fridge while driving might reveal something. A temp rise that large indicates the fridge has little cold food, a door seal leak, or is completely off most of the time.

Steve

ps. Note airflow past the door or vent will cause low pressure zones in the combustion chamber. If the pressure is lower at the base of the stack than at the top, the disruption may prevent the flame from heating the coils. Just the natural convection due to the heating will allow proper airflow when not moving.

Re: 2004 MB fridge not performing well on propane while driving

Reply #4 – April 28, 2021, 06:11:02 pm

Quote from: John DaCrema - April 28, 2021, 02:30:10 pm

I’ll start with the simple things you likely already checked.
Is there enough room for the fridge to have good air circulation? The warm air goes up and the cold air goes down due to relative density. There are no stock fans to push the air around.
Has the sensor that sits on the fins moved down over the years? The holder on my fridge cracked. When I got a new one I was amazed how much cooler it stayed. Turns out when loading I accidentally moved the sensor.
Are you driving or facing west for most of the day? Sun beating on the compartment could be an issue for an older fridge. When in camp try to get that side away from the direct sun. If that is not possible consider getting a couple large blue ice (Igloo or some such brand) things used in ice cooler. Keep one in the freezer and the other in the refrigerator. Swap as needed.
John

"Has the sensor that sits on the fins moved down over the years? The holder on my fridge cracked. When I got a new one I was amazed how much cooler it stayed. Turns out when loading I accidentally moved the sensor." The thermistor.

Re: 2004 MB fridge not performing well on propane while driving

Reply #5 – April 28, 2021, 06:17:00 pm

"When the LD is stationary, the fridge temperature range is 32 to 36 F with either electric or propane... However, the fridge does not cool [on propane] when the LD is in motion."

Well, there you go! Apparently the fridge is working normally except while under motion. That leads me to believe air flow up the flue behind the fridge is not as it should be while driving. As was said some folks have determined that muffin fan/s in the stack is helpful. Can't say why this would be true for some but not for others. You might take a drive to Oz and ask the Wizard!

Or you could do a search on this board for similar problems, I recall that this is not the first complaint of this nature.

Re: 2004 MB fridge not performing well on propane while driving

Reply #6 – April 28, 2021, 06:20:53 pm

"The thermistor."

Ah yes, the thermistor... that thingy clamped to the last fin in the fridge box. Slide it up for cooler operation or down for less. ? I think that's the way it works.

But because the Op says it works normal while stationary I'd rule that out.

Re: 2004 MB fridge not performing well on propane while driving

Reply #7 – April 28, 2021, 07:15:13 pm

Quote from: Steve - April 28, 2021, 03:30:00 pm

To diagnose the issue, I would try to duplicate the driving conditions that might cause the issue. Start by placing a fan outside the fridge outside access door, blowing from front to back, and check temps over a few hours. If that is not the issue, it may be the airflow past the roof vent, so try the test up there. if that test is also negative, you will need 2 fans for the logical next step. Then, if airflow appears to NOT be the issue, a voltmeter monitoring the 12V to the fridge while driving might reveal something. A temp rise that large indicates the fridge has little cold food, a door seal leak, or is completely off most of the time.

Steve

ps. Note airflow past the door or vent will cause low pressure zones in the combustion chamber. If the pressure is lower at the base of the stack than at the top, the disruption may prevent the flame from heating the coils. Just the natural convection due to the heating will allow proper airflow when not moving.

Thank you Steve. I have investigated on the air flow pass the vent door. Initially the heater temperature was significantly lower when the fridge operates on propane while driving, only around 98-110F vs 150F in the solar electric mode. I have since blocked two out of three vent slot groups on that door, leaving only the front slots open. Now the heater temperatures are almost the same for either propane or solar electric while driving but the fridge performance is still so bad. We drove from Orlando FL to Bryon GA during day time, fridge was in 32-36F range. Then when we drove from Byron GA to Cartersville GA in the evening in the propane mode, fridge temperature rose to 42F while heater temperature remained both at about 150F same as when the LD is parked. I have cleaned the the propane burner but I suspect there are somethings inside the propane burner block the heat transfer into the ammonia solution. I do not know how to fix this one or can it be fixed? The electric heating element seems does not have this issue as heat transfer appear to be efficient, any insight?

Re: 2004 MB fridge not performing well on propane while driving

Reply #8 – April 28, 2021, 07:30:36 pm

Quote from: Lazy Bones - April 28, 2021, 06:17:00 pm

"When the LD is stationary, the fridge temperature range is 32 to 36 F with either electric or propane... However, the fridge does not cool [on propane] when the LD is in motion."

Well, there you go! Apparently the fridge is working normally except while under motion. That leads me to believe air flow up the flue behind the fridge is not as it should be while driving. As was said some folks have determined that muffin fan/s in the stack is helpful. Can't say why this would be true for some but not for others. You might take a drive to Oz and ask the Wizard!

Or you could do a search on this board for similar problems, I recall that this is not the first complaint of this nature.

Thank you Steve S. I suspect over cooling and insufficient heat from propane burner initially. I have since partly blocked the front edge of the fridge roof vent, partially blocked side vents on the fridge door. But the problem is still there, only during driving. I think the propane burner does not transfer sufficient amount heat into the ammonia solution when the LD is in motion. I did not want to completely block the side door vents as it will cause other problems. Anyone has experience replacing the propane burner heat absorption unit?

Re: 2004 MB fridge not performing well on propane while driving

Reply #9 – April 28, 2021, 07:55:02 pm

The fridge depends on a chimney effect for cooling. You need air entering at the bottom of the stack, flowing up and over the cooling unit, and entering out the vent at the top.

On a MB unit, something about the placement of the vent and highway speeds interferes with this flow.

One fix that many of us have used is to add small fans to maintain chimney air flow while driving. Somewhere in the archives is talk about adding a air dam along the leading edge of the fridge vent in an attempt to disrupt the highway air flows and let the chimney effect work.

Blocking air flow up the chimney is counterproductive. You need to encourage air flow for cooling to work well.

Rich

Re: 2004 MB fridge not performing well on propane while driving

Reply #10 – April 28, 2021, 08:24:41 pm

Quote from: rich - April 28, 2021, 07:55:02 pm

The fridge depends on a chimney effect for cooling. You need air entering at the bottom of the stack, flowing up and over the cooling unit, and entering out the vent at the top.

On a MB unit, something about the placement of the vent and highway speeds interferes with this flow.

One fix that many of us have used is to add small fans to maintain chimney air flow while driving. Somewhere in the archives is talk about adding a air dam along the leading edge of the fridge vent in an attempt to disrupt the highway air flows and let the chimney effect work.

Blocking air flow up the chimney is counterproductive. You need to encourage air flow for cooling to work well.

Rich

Thanks for you suggestion, I thought the same initially, I put two small 12v dc fans between the cooling coils on the back of the fridge but they did not solve the problem in the propane mode. In fact they made the heater performance worse indicated by the low 95F heater temperature, insufficient to boil ammonia off from the solution. Managing correct amount of cooling air flow seems to be much more critical for propane than solar electric mode while driving. I still do not have a solution. The fridge works fine as long as the battery can support the electric heater at any highway speed but when the battery voltage is low and I have to switch to propane, the problem starts...

Re: 2004 MB fridge not performing well on propane while driving

Reply #11 – April 28, 2021, 08:39:46 pm

I have not experienced your problem when we drove using propane, but now I too run the fridge through an inverter while driving. However, mine is dedicated to this function and essentially runs off the alternator, with an automatic transfer switch from shorepower to inverter. The inverter only powers up when there is output from the alternator. This way, I don't have to worry about forgetting and drawing down any batteries.

Steve

Re: 2004 MB fridge not performing well on propane while driving

Reply #12 – April 28, 2021, 08:46:18 pm

If you're convinced that the propane burner isn't generating enough heat, the common things to check would include the propane pressure coming from the regulator, the air/fuel mixture at the burner, and the burner orifice which sometimes gets gummed up (search for proper cleaning instructions since changing the orifice size even slightly can compound your problems).

It's also possible that your 2004 fridge is just nearing the end of it's life and doesn't cool as well as it did before (because the ammonia solution doesn't flow as freely through the passages inside the cooling unit anymore).

Since you only have problems while driving, and many other MB owners have experienced similar issues, it's at least worth considering that your issue could still have a similar cause to that of the others.

Rich

Re: 2004 MB fridge not performing well on propane while driving

Reply #13 – April 28, 2021, 09:03:38 pm

With the robust solar and battery capacity you have, you might consider a 12 V / 120 V compressor fridge such as a Vitrifrigo DP-150. I've had this type of fridge in several rigs, and have never had a problem with them not cooling while underway.

They don't use a lot of power (about 5 amps, compared with 30+ amps when running your present fridge from an inverter). They're not affected by being off-level. They don't catch fire. And of course they use no propane at all. :-) It's nice to have a refrigerator that's entirely powered by the sun.

Re: 2004 MB fridge not performing well on propane while driving

Reply #14 – April 28, 2021, 09:08:08 pm

"It's also possible that your 2004 fridge is just nearing the end of it's life and doesn't cool as well as it did before..."

Rich may be onto something here. Is your fridge the original, now 17 years old? My 30'IB is also a 2004 and I long ago (2-3 yrs) replaced my fridge. But my ammonia line ruptured when it went. Sniff around and try to detect an odor of rotten eggs.

Re: 2004 MB fridge not performing well on propane while driving

Reply #15 – April 28, 2021, 09:11:57 pm

Quote from: Steve - April 28, 2021, 08:39:46 pm

I have not experienced your problem when we drove using propane, but now I too run the fridge through an inverter while driving. However, mine is dedicated to this function and essentially runs off the alternator, with an automatic transfer switch from shorepower to inverter. The inverter only powers up when there is output from the alternator. This way, I don't have to worry about forgetting and drawing down any batteries.

Steve

I really like your solution! Will try to see if I can do the same, your rig must have a more powerful alternator. The fridge heater is rated as 400w, hope our 2004 MB's E450 can support, may have to bypass the diod.

Re: 2004 MB fridge not performing well on propane while driving

Reply #16 – April 28, 2021, 09:18:23 pm

Quote from: Lazy Bones - April 28, 2021, 09:08:08 pm

"It's also possible that your 2004 fridge is just nearing the end of it's life and doesn't cool as well as it did before..."

Rich may be onto something here. Is your fridge the original, now 17 years old? My 30'IB is also a 2004 and I long ago (2-3 yrs) replaced my fridge. But my ammonia line ruptured when it went. Sniff around and try to detect an odor of rotten eggs.

Thank you Steve S. Our fridge is the original, what puzzles me is the fact it performed really well when parked in both electric or propane mode, works fine with solar electric when driving, only refuse to work with propane when driving. BTW, I was crazy enough to put a camera near the burner to make sure I can see the flame when driving. The flame was on all the time as temperature rise during the whole trip. One explanation could be the propane heater is too old and somehow block the heat into the ammonia solution.

Re: 2004 MB fridge not performing well on propane while driving

Reply #17 – April 28, 2021, 10:37:19 pm

"One explanation could be the propane heater is too old and somehow block the heat into the ammonia solution."

This seems unlikely since it works on LP when stopped.

"the fridge has been this way since we bought it in 2011".

Did it come from a place that was well above sea level, Denver for example? Maybe the fuel\air mixture was adjusted for operation there, which would not be ideal for lower altitudes. It (the burner) might be just efficient enough when stopped, but not when under way, and other forces at work. You mentioned a camera on the flame when under way. Is it a strong blue flame, or is it 'lazy' with some yellow in it?

Just a thought. Good luck!

Bill

Re: 2004 MB fridge not performing well on propane while driving

Reply #18 – April 28, 2021, 11:10:15 pm

Quote from: cli288 - April 28, 2021, 09:11:57 pm

I really like your solution! Will try to see if I can do the same, your rig must have a more powerful alternator. The fridge heater is rated as 400w, hope our 2004 MB's E450 can support, may have to bypass the diod.

The 130A alternator can produce up to 1500W, plenty for all systems. The inverter I use is about 850W, but since it only powers the fridge, about 450W is the draw when the fridge cycles on.

Steve

Re: 2004 MB fridge not performing well on propane while driving

Reply #19 – April 29, 2021, 05:29:55 am

Quote from: krmugn - April 28, 2021, 10:37:19 pm

"One explanation could be the propane heater is too old and somehow block the heat into the ammonia solution."

This seems unlikely since it works on LP when stopped.

"the fridge has been this way since we bought it in 2011".

Did it come from a place that was well above sea level, Denver for example? Maybe the fuel\air mixture was adjusted for operation there, which would not be ideal for lower altitudes. It (the burner) might be just efficient enough when stopped, but not when under way, and other forces at work. You mentioned a camera on the flame when under way. Is it a strong blue flame, or is it 'lazy' with some yellow in it?

Just a thought. Good luck!

Bill

Bill, you hit the nail on the head! The unit came from Mr and Mrs John and Mary White who were the original owners and members of the Yahoo group. The were based in the Boston area. The flame, is blue not yellow but I feel a bit lazy, I am not sure how to adjust the flame air to fuel ratio. I think the flame is just sufficient to heat up when the LD is stationary but when too much air flow through the heater chamber, it sucks out too much heat. The flame is burning all the time but never seem to be enough at highway speed. The electric heater element is sealed, thus not affected. Any idea on how to adjust propane air to fuel ratio? Being an automotive engineer in my pre-retirement life I know how to adjust air/fuel ratio in a car but do not know where is the propane adjustment valve in the burner. Thanks for you insightful input!

Re: 2004 MB fridge not performing well on propane while driving

Reply #20 – April 29, 2021, 05:42:54 am

Quote from: Steve - April 28, 2021, 11:10:15 pm

The 130A alternator can produce up to 1500W, plenty for all systems. The inverter I use is about 850W, but since it only powers the fridge, about 450W is the draw when the fridge cycles on.

Steve

Thanks again Steve. I will try a couple of things to follow your way, first is to bypass the diod and get the alternator directly to a dedicated inverter to power the fridge while driving. Our current 2kw pure sine wave Magnum inverter has too much parasitic loss to operate this way (4.5 amps just to keep it on).

Re: 2004 MB fridge not performing well on propane while driving

Reply #21 – April 29, 2021, 01:41:11 pm

"I am not sure how to adjust the flame air to fuel ratio."

I remember trying to do this on my propane fridge when camping at 10,000', but I never could figure out a way. (The problem turned out to be a bad thermistor, but that's a different story.) On a water heater it's easy--just slide the slotted sleeve. But on a fridge...? I'd be interested to know how this is done.

Re: 2004 MB fridge not performing well on propane while driving

Reply #22 – April 29, 2021, 02:40:02 pm

Hi cli228; This is a common issue with the MidBath. I'm sure it is related to air turbulence right at the refrigerator vent cap. Along with general ageing there could be a build up of rust inside the chimney, and on the spiral deflector inside. Instructions say to clean it every now and then. A 'drive time' inverter would be good here, since you have so much solar. RonB

Re: 2004 MB fridge not performing well on propane while driving

Reply #23 – April 29, 2021, 03:39:03 pm

Quote from: RonB - April 29, 2021, 02:40:02 pm

Hi cli228; This is a common issue with the MidBath. I'm sure it is related to air turbulence right at the refrigerator vent cap. Along with general ageing there could be a build up of rust inside the chimney, and on the spiral deflector inside. Instructions say to clean it every now and then. A 'drive time' inverter would be good here, since you have so much solar. RonB

Thank you Ron B. Now I get a clear picture of what to do, basically pursue a dedicated run time inverter to power the fridge during highway travel. I did clean the burner with compressed air but did not know what else to do (afraid of too much mechanical cleaning would cause a leak). I did seal the front edge of the top vent to reduce the suction turbulence but it seemed w/o much effect. Thanks to everyone's input and I will share my progress once the dedicated inverter is installed and wired up.

Re: 2004 MB fridge not performing well on propane while driving

Reply #24 – April 29, 2021, 05:18:29 pm

Quote from: Andy Baird - April 28, 2021, 09:03:38 pm

With the robust solar and battery capacity you have, you might consider a 12 V / 120 V compressor fridge such as a Vitrifrigo DP-150. I've had this type of fridge in several rigs, and have never had a problem with them not cooling while underway.

They don't use a lot of power (about 5 amps, compared with 30+ amps when running your present fridge from an inverter). They're not affected by being off-level. They don't catch fire. And of course they use no propane at all. :-) It's nice to have a refrigerator that's entirely powered by the sun.

Thank you Andy. We have a long term plan to change to a compressor fridge once the current one is too old to fix. What deter us is the replacement process, have to take out the fridge from the dining area window. It will be a very messy procedure. Currently we have no motivation to make this jump yet.

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