I have a residential refrigerator in the motorhome. I was thinking of putting a switch on the defrost heater so it could be turned off for the times we are overnight parking while traveling to save some battery power. Has anyone done this or have an opinion pro or con? Thanks.dreamer.

Defrost heaters do not run that much. In the OLD refer mechanical control's, the defrost heaters were on a mechanical timer. In the newer electronic control refers, I would bet it is on a temp sensor control instead of a timer, but you need to find out. The purpose of the defrost heaters is to remove the ice buildup from the evaporator/s. The ice restricts the air flow thru the evap fins and causes a loss of cooling in the refer. So, if you turn the Heaters OFF, you may cause a faster ice build up and that would cause the refer to run LONGER to maintain your temp. So, it would be a trade off on power consumption----either the defrost heater would run or the compressor would run longer due to the defrost heater not removing the ice build up. Doug

It is like regeneration mode on modern diesels. You don't want it to click uphill. I think the best way would be program the controlled to not go into defrost at those days. Household refrigerators have never been intended for it, but I would start with giving manufacturer a call and ask for engineer. They might want to charge you for advise, or maybe hoping for more buyers will provide free help.Doug is right that putting just a switch you will fool the computer with hard to predict consequences.

i have not done anything to minebut several other members haveaccording to the wiring diagram mine is a motorized timer, since we full time i just left it alone, i don't know how often it cyclessomeone once posted 10 minutes every 10 hoursIDK, but i;ve never been much concerned about, and we dry camp 95 percent of the timeright now the fridge is empty and turned off, the RV is at the diesel shopdespite CPU technologyNOT everything has a CPU chip in it

MrWizard wrote:i have not done anything to minebut several other members haveaccording to the wiring diagram mine is a motorized timer, since we full time i just left it alone, i don't know how often it cyclessomeone once posted 10 minutes every 10 hoursIDK, but i;ve never been much concerned about, and we dry camp 95 percent of the timeright now the fridge is empty and turned off, the RV is at the diesel shopdespite CPU technologyNOT everything has a CPU chip in itTypical defrost cycle 10 minutes per 10 hrs of COMPRESSOR ON TIME is what I measured with my 10 cu ft fridge..And yes, I HAVE rewired mine with a DPDT toggle switch to allow me to temporarily disable the defrost timer. The defrost heater on mine draws 250W.. I only have one pair of 6V GC batteries so I wanted to make sure that would be plenty of capacity for overnighting without shore power.OP does need to be aware, SOME fridges use mechanical timers and some fridges use an electronic timer, mine uses a mechanical timer so I cannot guarantee if bypassing is possible with electronic timer.You will have to study the wiring diagram (which should be glued to the back of the fridge) in order to determine how to connect a disable switch. I had to use a DPDT switch because of how the timer contacts work on mine, somehow the timer motor connected real oddly on mine, hence the extra pole on the switch.I only disable while traveling, you MUST re-enable the timer at the earliest chance you get. Otherwise you will risk major ice buildup in the coils.. I would say you could go perhaps two to three days without the defrost enabled, after that the build up will make the compressor run longer and longer. You could go longer in dry climates but in high humidity areas like at the beach you will get build up very fast.On edit.. Added in electrical diagram of my fridge, before and after mod..Note, I had to add a jumper to the contacts of the DPDT switch..

My Maytag has a Vacation Mode, which decreases the defrost cycles. I use this when we dry camp overnight.

Has anyone put a switch on a refrigerator defrost heater?

15 Replies

Gdetrailer
Explorer III
May 15, 2016
fairway2002 wrote:
just a FYI Defrost Cycle does also take care of you frost free option

Sort of.

So called "frost free" fridges are not really "frost free"..

Instead they should be called "automatic defrost" fridges.

Manual defrost fridges typically have the cooling coils exposed to the inside of the fridge.

"Frost free" fridges HIDE the coiling coils behind a false wall in the back of the freezer. The fridge and freezer air is circulated by a small fan located at the coils in the freezer.

These coils will build up frost and eventually the frost turns to ice from the on/off cycles of the compressor. As ice builds you get less cooling resulting in longer compressor on times.

Hence the need for a defrost cycle..

To make the defrost cycle faster the coils are equipped with a small 200W-250W heating element. When defrost cycle is on, the compressor is turned off and the heating element is turned on.

Defrost cycle only happens when the fridge T stat calls for cooling AND the timer has timed out the 10hrs or so of compressor run time.

By adding a switch to disable the defrost cycle I am reducing the chance of the defrost heater using up extra battery capacity while I am traveling and or overnighting. This allows me to run with only one pair of GC batteries instead of two pairs and not having to worry about running out of battery when overnighting due to an unexpected defrost cycle. A significant savings in weight and cost.

I have also tested how long I can allow the defrost cycle to be turned off before the ice builds up too much.. Typically 5 to 6 days, any more than that the compressor will start running longer and things in the freezer like ice cream get too soft.

It will not cause any harm by TEMPORARILY disabling the defrost cycle for a few days.

I simply turn off the defrost when I disconnect from shore power, I leave it off while I am driving and even when stopping overnight without shore power.. Once I get to my destination with shore power I turn the defrost back on..

The main thing is to remember to switch the defrost back on.
Gdetrailer
Explorer III
May 15, 2016
dreamer wrote:
Thanks for all of the responses. A big thank you to Gdetrailer for the wiring diagram. I'm nearing the departure date for our Alaska trip and may wait to try to add a switch until our return. Thanks again!

dreamer.

You are welcome!

You will need to check the diagram on your fridge since it could be a bit different from mine depending on the timer switching action.
Gdetrailer
Explorer III
May 15, 2016
MrWizard wrote:
look close
the jumper he put on the switch, keeps power to the compressor available

Correct.

Made the drawing and forgot to annotate and highlight the needed jumper.

Thanks MrWizard for clarifying it!
fairway2002
Explorer
May 15, 2016
just a FYI Defrost Cycle does also take care of you frost free option
dreamer
Explorer
May 15, 2016
Thanks for all of the responses. A big thank you to Gdetrailer for the wiring diagram. I'm nearing the departure date for our Alaska trip and may wait to try to add a switch until our return. Thanks again!

dreamer.
MrWizard
Moderator
May 15, 2016
look close
the jumper he put on the switch, keeps power to the compressor available
Kayteg1
Explorer II
May 15, 2016
Gdetrailer wrote:

It doesn't take a rocket scientist to figure out the wiring and how it works..

Maybe yes, maybe not.
From what I see on Gdetrailer drawing, his switch disconnects everything but light in the fridge.
I hope this is just bad scale on drawing and the first contact can switch over to the 2nd prong.
Gdetrailer
Explorer III
May 14, 2016
wa8yxm wrote:
I would recommend against it, though it woudl be very easy to do I will recommend against it... here is why:

On my last Residential Fridge (IN my last Residence) said heater failed.

MAJOR REPAIR.. Had to call the appliance fix it guy, Had to find parts he did not have in stock, he replaced the heater, and a fan and some other stuff,

Of course the thing was not working right when it failed.

I do not like paying professionasls for repasir at over 100/hr.

Absolutely puzzled at your response.

Not sure how you can link your bad heater to someone adding a simple switch that merely allows one to temporarily turn the heater off.

It doesn't take a rocket scientist to figure out the wiring and how it works.

Adding a switch in no way, shape or form can damage or blow out the heating element..
dougrainer
Nomad
May 13, 2016
wa8yxm wrote:
I would recommend against it, though it woudl be very easy to do I will recommend against it... here is why:

On my last Residential Fridge (IN my last Residence) said heater failed.

MAJOR REPAIR.. Had to call the appliance fix it guy, Had to find parts he did not have in stock, he replaced the heater, and a fan and some other stuff,

Of course the thing was not working right when it failed.

I do not like paying professionasls for repasir at over 100/hr.

WHY is this story related to adding a switch???????????????????????? Doug
wa8yxm
Explorer III
May 13, 2016
I would recommend against it, though it woudl be very easy to do I will recommend against it... here is why:

On my last Residential Fridge (IN my last Residence) said heater failed.

MAJOR REPAIR.. Had to call the appliance fix it guy, Had to find parts he did not have in stock, he replaced the heater, and a fan and some other stuff,

Of course the thing was not working right when it failed.

I do not like paying professionasls for repasir at over 100/hr.