TheSamba.com :: View topic - Will my fridge work better if the cooling fan is always on?

Sun Aug 28, 2016 7:19 pm

Before I rig this up, will my fridge be colder if I add a switch to keep the cooling fan always on?

Also, if I put some computer case fans in there, should I add a fan to both the lower and upper heatsinks, or just the lower one?

Mon Aug 29, 2016 10:18 am

My stock fan started squeaking on a road trip far from home. It was annoying. Not having ever pulled a fridge, I though I could get some WD 40 on the fan bearing. I took the vent from the side of the cabinet. Could not even see the fan.

Next idea was to remove one of the plastic service ports from the side of the van. Within a minute of removing the service port, the fan stopped running. I still could not see the fan. Reinstalled the service port and within a couple minutes the fan was running again. Remove the port and fan shuts off.

From that exercise, I determined it was more important to get the heat out from behind the fridge to improve it's function. When I got home, I pulled the fridge and added a computer fan to the bottom coils. Copying another member's idea, I made a shroud to direct all the flow across the fins. I connected it to the stock thermal switch, but added a toggle I could manually operate it.

I then cut apart the city water supply port and added a computer fan to it. It is also connected the toggle I installed. The toggle is actually a two way switch, Middle is fan runs off of temp switch as stock, switch down bottom fridge fan only, switch up, bottom fan and exhaust fan.

When it is hot and I am driving, I will run the fridge fan continuously. Camped, I open the cover on the service port and run both fans. My wife says the fridge is working better since adding the fans. Not scientific, but she used to say, "the fridge does not feel cold". So I call that an improvement.

Mon Aug 29, 2016 11:21 am

the fan is most useful to be on when the compressor is running, remember it cycles on and off via the thermostat. having a fan blowing on the hot cools when nothing hot is passing thru them (ie compessor off) should not improve the fridges ability to cool. now if the stock fan is undersized, such that the hot coil is not disapating heat well, then a more powerful fan (improved cooling air flow) may be of benifit to you.

also a clean coil will operate much better than a dirty one lint and dust can adversely effect the cooling even in a thin layer.

good luck, keep your cool.

Mon Aug 29, 2016 11:41 am

bluebus86 wrote: the fan is most useful to be on when the compressor is running, remember it cycles on and off via the thermostat.

Remember, the Dometic installed in full-campers is not a compressor fridge; it is an absorption fridge: http://vintageservelrefrigerators.8k.com/HowItWorks.html . The Dometic's fan cycles via a thermo-switch.

As for the fan(s), many different methods are out there: one fan, two fans, exhaust fan via city water hookup, interior fridge fan, etc. Each fridge is kind of like the vans: Each has its own temperament and needs. :lol:

Potentially helpful topic: http://www.thesamba.com/vw/forum/viewtopic.php?p=7762985 .

Mon Aug 29, 2016 12:41 pm

I've probably mentioned this before - but my fan quit working about 10 or 15 years ago and I can't tell the difference.

My Dometic fridge cools fine even in desert heat.

I do have a muffin fan inside the fridge but that is just to circulate air around the contents for more even cooling.

Mon Aug 29, 2016 12:56 pm

kamzcab86 wrote: bluebus86 wrote: the fan is most useful to be on when the compressor is running, remember it cycles on and off via the thermostat.

Remember, the Dometic installed in full-campers is not a compressor fridge; it is an absorption fridge: http://vintageservelrefrigerators.8k.com/HowItWorks.html . The Dometic's fan cycles via a thermo-switch.

As for the fan(s), many different methods are out there: one fan, two fans, exhaust fan via city water hookup, interior fridge fan, etc. Each fridge is kind of like the vans: Each has its own temperament and needs. :lol:

Potentially helpful topic: http://www.thesamba.com/vw/forum/viewtopic.php?p=7762985 .

yes, I forgot not all fridges are same type, i got a 12 volt dc / 120 volt ac freon fridge in my camper van. true there is no compressor in the ammonia type systems like in many vans, but same holds, the fan should should be on only when the fridge is actually cooling, which often is not all the time. this applies regardless if a compresser or ervaporater type of fridge.

Mon Aug 29, 2016 1:35 pm

MarkWard wrote: My stock fan started squeaking on a road trip far from home. It was annoying. Not having ever pulled a fridge, I though I could get some WD 40 on the fan bearing. I took the vent from the side of the cabinet. Could not even see the fan.

Next idea was to remove one of the plastic service ports from the side of the van. Within a minute of removing the service port, the fan stopped running. I still could not see the fan. Reinstalled the service port and within a couple minutes the fan was running again. Remove the port and fan shuts off.

From that exercise, I determined it was more important to get the heat out from behind the fridge to improve it's function. When I got home, I pulled the fridge and added a computer fan to the bottom coils. Copying another member's idea, I made a shroud to direct all the flow across the fins. I connected it to the stock thermal switch, but added a toggle I could manually operate it.

I then cut apart the city water supply port and added a computer fan to it. It is also connected the toggle I installed. The toggle is actually a two way switch, Middle is fan runs off of temp switch as stock, switch down bottom fridge fan only, switch up, bottom fan and exhaust fan.

When it is hot and I am driving, I will run the fridge fan continuously. Camped, I open the cover on the service port and run both fans. My wife says the fridge is working better since adding the fans. Not scientific, but she used to say, "the fridge does not feel cold". So I call that an improvement.

Nice looking shroud for sure. Do you have the plans for that?

Mon Aug 29, 2016 5:14 pm

The rear cooling fan on the Dometic 182B is supervised by a bi-metal thermostatic switch which closes (on) when the metal fins of the condenser reaches 126°F and opens (off) at 108°F. Ideally, the fan never has to run because the condenser heat sink can be cooled adequately via convection only. However, if the outside air temperature is above ~80°F then convective air flow will be minimal and the fan will cycle on and off to keep the condenser within that temperature range. So, with the fan always running, you will get the forced air cooling you need, but you will be inputting more electrical energy than is necessary for the refrigeration process. If you find the constant on/off cycling of the fan to be annoying, then it's a good idea to install a bypass switch and let the fan run constantly, but remember that you are actually decreasing the energy efficiency of the fridge by doing so.

For a given gas/electric thermostat set-point, the interior of the fridge should be slightly cooler with the fan always on than with it cycling.

Remember that this fridge is designed to cool via convection and the fan is essentially a backup for when convective airflow is insufficient to cool the condenser.

From the Dometic Service Manual...."The importance of adequate air flow across the cooling unit cannot be emphasized too much. A minor restriction in the venting system will not create a problem on cooler days - the available air flow will still provide adequate cooling due to the lower air temperature. However, on a hot day (90°F or more) even a minor restriction will cause overheating of the cooling unit and the refrigeration process will slow down or stop."

Think about the things that will help establish convective air movement:

1. Venting air space under the fridge is free from debris and it not blocked by bags, gear, etc.
2. Interior air of the van is as cool as possible (parked in the shade)
3. Air pockets behind the fridge have been blocked off to create as much of a chimney effect as possible by keeping air flow as laminar as possible.
3. Warm air vents at the top and side of the fridge are unblocked.

Tue Aug 30, 2016 5:06 am

Interesting theory on how the stock fan assists the fridge operation. So it would appear running it in high temps continuously serves no benefit. I did leave the stock sensor and the original fan died. If you look at the bottom of the shroud there are holes to allow normal convection.

No plans, but this member has some very ingenious vanagon mods. I copied what he had done to improve his domestic. http://www.griffco.ca/interest/vw/vwmods.htm[/b]

Tue Aug 30, 2016 11:00 am

The stock Dometic refrigerator rear fan has nothing to do with its cooling system mechanism.
It is completely switched on and off thermostatically, determined by the temperature of air behind the refrigerator and the van. This fan will come on
even when fridge is not running. Best to cool using fan in water port.

Tue Aug 30, 2016 11:29 am

DLJ wrote: The stock Dometic refrigerator rear fan has nothing to do with its cooling system mechanism.
It is completely switched on and off thermostatically, determined by the temperature of air behind the refrigerator and the van. This fan will come on
even when fridge is not running. Best to cool using fan in water port.

What is the fan for?

Tue Aug 30, 2016 11:38 am

MarkWard wrote: So it would appear running it in high temps continuously serves no benefit. That's not the point I was trying to impart in my previous post. With high outdoor air temperatures, running the condenser cooling fan continuously will definitely improve the fridge's performance and allow it to push a larger temperature differential. However, it's good to understand that for lower outdoor air temperatures, the Dometic can operate effectively without any forced air cooling.

DLJ wrote: The stock Dometic refrigerator rear fan has nothing to do with its cooling system mechanism. Incorrect. The refrigerator condenser cooling fan is definitely a component of the refrigerator's cooling system mechanism.

DLJ wrote: It is completely switched on and off thermostatically, determined by the temperature of air behind the refrigerator and the van. This fan will come on even when fridge is not running. Correct. Sort of. The thermostatic switch is attached to the condenser's metal heat sink fins. When the thermostatic switch reaches 126°F it will close and the fan will operate. This occurs regardless of whether the refrigerator is actually in a cooling mode. If the van is parked in the sun on a hot day, the air temperature between the fridge and the van wall can exceed 126°F which heats the switch to 126°F and the fan operates. Adding a dollop of thermal paste between the thermostatic switch and the condenser heat sink fins will keep this from happening as readily as the thermal paste helps to thermally couple the switch to the heat sink so that the switch will operate based on the temperature of the condenser heat sink metal and not simply the temperature of the air in that space. Westfalia did not use thermal paste in the original switch application. This is a cheap and easy upgrade that improves the operation of the cooling system.

Tue Aug 30, 2016 11:40 am

On our Dometic, the temp switch for the fan is attached to one of the upper cooling fins. Granted high ambient can trigger it, but I can't imagine the Dometic engineers would have attached it to a fin if they intended it to only trigger off of ambient temp. They could have attached it to the housing instead.

As I said earlier, my wife believes the fridge is working better. That is good enough for me. Certainly not as scientific though.

Tue Aug 30, 2016 11:58 am

OK I agree that fan is part of operating mechanism if viewd as a means to
increase refrigerator efficiency. ie fans job is to reduce heat in back of fridge.
But refrigerator will work without fan, just not as well.

Tue Aug 30, 2016 3:05 pm

at ambeint temps of over 100F the heat transfer is really reduced, temps of 120 F are common in a van parked in the sun on a hot day, specially a dark painted van. so the fridge looses effeciency when it is hot, it cant tranfer the heat as well, and there fore will have to run more and it will have a limit wjere it is just to hot an ambeint to allow it to reach cold setpoint.

also a hot van does not help the fridge stay cool, they are usually not super insulated.

to improve efficncey more insualtion could be added.

also use window shades in the sun to keep van cool.

also as space allows, fill the fridge with frozen water in plastic jug(s). this will go a long way to conserving your propane and help keep thing cooler specially when weather is super hot.

also many RVers know that since these ammonia type fridges are very slow to cool things, that it is best to only add already cold food to the fridge, adding a six pack of warm drinks can cause the fridge to increase in temp a considerable amount, it will take a long time for the temp in the whole fridge to recover and to cool the warm drinks. so always only add cold or froozen food, dont ask your rv fridge to do the work of cooling warm stuff down, rather think of it as an ice box that has limited capacity too cool things.

the evaporative fridge performs completely different than a house hold compressor type fridge. house hold types using freon or freon replacements have a much more efficient cycle for cooling than an rv type ammonia fridge. if you understand their behavior and practicing only adding cold food, by helping out in hot weather by adding an ice block, and taking steps to keep van cool, you will be able to get more cold goodness out of your rv fridge. they have advantages in that they sip energy unlike a compressor fridge, but they have limiitation in both cooling capacity (they are slow to cool) and they rapidly loose efficiency in hot weather, just when you need them most.

Tue Aug 30, 2016 5:14 pm

bluebus86 wrote: also a hot van does not help the fridge stay cool, they are usually not super insulated.

to improve efficncey more insualtion could be added.

also use window shades in the sun to keep van cool...

This helps too (secured with magnets):

I try to park pointing south (easy to do on the Pacific) as that gets best exposure for my solar panel and also subjects the fridge to sun only in the morning. Also gives you a great ocean view.