Fridge Won't Cycle On and Off

[boatman61]

It will still run if there's nothing there to trip a switch to OFF....

[Richard Kollmann]

If compressor does not cycle off and every thing in refrigerator freezes there is a problem with thermostat, YES.

[Annie2020]

It was fine but seemed a little warmer yesterday morning
so moved the sensor closer to the box. Now it doesnt cycle anymore. Help please?

[Annie2020]

So should the sensor be further away? Surely this would make it run longer?

[Richard Kollmann]

Originally Posted by Annie2020

So should the sensor be further away? Surely this would make it run longer?

Thermostats are not the same as for controlling box temperatures in pleasure boats. All icebox conversion refrigeration thermostats must be calibrated by mechanical adjustment or on digital electronic thermostat by establishing a correction offset factor. In either case thermostat dial settings must be changed as refrigerator exterior ambient temperatures change. The control knob on conventional thermostat is numerical generally from Off then on one to ten and not in degrees temperature. A good thermostat set up on a standard day temperature would be dial setting of 3 to 4 allowing room to compensate for colder or warmer weather.

Most boat refrigerators have conventional thermostats that control when compressor runs and when it stops. These thermostats control Evaporator temperature and are not designed to control box temperature but energy efficiency because box interior heat varies. Thermostats with conventional evaporators are calibrated by the amount of thermostat sense tube in contact with evaporator. With electronic thermostats measuring box temperature requires a correction reference chart similar to a compass deviation card or rely on box calibrated thermometers.

I have always believed a good mechanical thermometer that can be calibrated to a desire temperature area of the box is best box temperature monitor.

For more info on refrigerator/freezers temperature control see TECH TIP #6 on my web site,, Kollmann Marine

[CassidyNZ]

I have a fridge unit with a ordinary ribbed evaporator that I installed with a mechanical thermostat 6 years ago. I have just installed a very similar unit as a freezer and in the process, changed to electronic control units.

Setup is simple, installation is simple, they’re inexpensive and they work a treat.

Note: I initially had one unit controlling both fridges but this limited me to having to have both units on or off so I switched to seperate controllers so that I could have the freezer off with the fridge still running.

These controllers have a defrost function (middle button LHS) if your refrigeration system supports it (mine doesn’t).

[Gtstricky]

Annie in case you were wondering... I don't understand Richard's answer either. Dang Richard can you dumb it down for us mere mortals?

[stormalong]

I have a couple of new Adler Barbour cold machine thermostats for sale.

For Sale: Adler Barber cold machine thermostats - Cruisers & Sailing Forums

[Coolerking]

If its the standard rollbond dry evaporator plate that comes preinstalled/ or came as a matched set with the condensing unit, and you have the thermostat that also came with the kit, then it is meant to be attached to a specific place on the evaporator plate.
You can find all this info online.

[Peter Mackay]

Originally Posted by CassidyNZ

I have a fridge unit with a ordinary ribbed evaporator that I installed with a mechanical thermostat 6 years ago. I have just installed a very similar unit as a freezer and in the process, changed to electronic control units.

Setup is simple, installation is simple, they’re inexpensive and they work a treat.

Note: I initially had one unit controlling both fridges but this limited me to having to have both units on or off so I switched to seperate controllers so that I could have the freezer off with the fridge still running.

These controllers have a defrost function (middle button LHS) if your refrigeration system supports it (mine doesn’t).

Great advice Cassidy, and simple. (KISS principle!)
Suggest checking cabinet for air leakage by simple placing a strong torch (Light) inside cabinet on a dark night. Note any areas light escapes and seal.
Next ditch the mechanical thermostat and replace with a digital type like Cassidy did. The digital ones are much more accurate, easy and accurate to set both cut-in and cut out temps, can be mounted remote and provide an LED temperature display so you will know what's happening in the cabinet. Look for like an Elitech STC8000 on Ebay, about $15

Thermostats of any type are simply on-off switches, temperature activated... no great mystery really.

Cheers Pete

[Richard Kollmann]

Originally Posted by Peter Mackay

Great advice Cassidy, and simple. (KISS principle!)
Suggest checking cabinet for air leakage by simple placing a strong torch (Light) inside cabinet on a dark night. Note any areas light escapes and seal.
Next ditch the mechanical thermostat and replace with a digital type like Cassidy did. The digital ones are much more accurate, easy and accurate to set both cut-in and cut out temps, can be mounted remote and provide an LED temperature display so you will know what's happening in the cabinet. Look for like an Elitech STC8000 on Ebay, about $15

Thermostats of any type are simply on-off switches, temperature activated... no great mystery really.

Cheers Pete

If you are an armchair sailor you can live with these electronic gadgets. If you are a blue water sailor who needs redundancy refrigeration reliability carry spare control devices to keep refrigeration operating.

[Peter Mackay]

Originally Posted by Richard Kollmann

If you are an armchair sailor you can live with these electronic gadgets. If you are a blue water sailor who needs redundancy refrigeration reliability carry spare control devices to keep refrigeration operating.

Wow! Psychiatry has obviously made some serious advances! Being able to determine classes of sailors by the type of thermostat used, amazing!

Seriously, mechanical thermostats, like crank handles, are a thing of the past.
Digital controllers allow accurate setting of cut out temperature and cut in temperature, provide a digital readout, have a start delay and are not subject to ambient variation, no mercury etc. Water proof models like the STC600 suit marine application.
Digital thermostats, like mechanical ones, are simply a switch and can service any refrigerator / refrigeration application, only better.

Cheers Pete

[Richard Kollmann]

Originally Posted by Peter Mackay

Wow! Psychiatry has obviously made some serious advances! Being able to determine classes of sailors by the type of thermostat used, amazing!

Seriously, mechanical thermostats, like crank handles, are a thing of the past.
Digital controllers allow accurate setting of cut out temperature and cut in temperature, provide a digital readout, have a start delay and are not subject to ambient variation, no mercury etc. Water proof models like the STC600 suit marine application.
Digital thermostats, like mechanical ones, are simply a switch and can service any refrigerator / refrigeration application, only better.

Cheers Pete

Pete, you may have something there about mental health of blue water sailors but I admire them. Yes I prefer reliable decisions based on equipment selection, Risk and Reward, for open water boats.

[slug]

Originally Posted by CassidyNZ

I have a fridge unit with a ordinary ribbed evaporator that I installed with a mechanical thermostat 6 years ago. I have just installed a very similar unit as a freezer and in the process, changed to electronic control units.

Setup is simple, installation is simple, they’re inexpensive and they work a treat.

Note: I initially had one unit controlling both fridges but this limited me to having to have both units on or off so I switched to seperate controllers so that I could have the freezer off with the fridge still running.

These controllers have a defrost function (middle button LHS) if your refrigeration system supports it (mine doesn’t).

Yup....Worthwhile installation ..

[conachair]

Originally Posted by Richard Kollmann

If you are an armchair sailor you can live with these electronic gadgets. If you are a blue water sailor who needs redundancy refrigeration reliability carry spare control devices to keep refrigeration operating.

Which is why i went over to an arduino (now esp32) as a thermostat after the mechanical broke after about 5 years, can do much, much more, costs less, easy to get spares - just get another one out of the box

JLCPCB sending a new board rather than perfboard, will allow to run at different RPM. And more than most will ever want or need, but sends all the data inculding voltage and current as signalk for logging, interesting to watch duty cycle after the beer goes in PCBs are about £20 for 5.
Will upload code & files for the PCBs if they turn up and actually work , current setup has been in for about decade with an arduino flawless so far .