Failed thermostat - Greunert fridge

[Calypso52]

Our fridge is a champ. Runs a fridge and separate freezer. Cold plates.
The thermostat has failed on the fridge side. All is normal on the freezer side. For the past few days, I have had to turn the analog knob higher to get it to turn on. Today, nothing. Stuck my head down in there and it looks like the copper (wire? thin tube?) runs from the dial to an item that connects to the coolant line. Some how the mechanism expands and contracts with temperature and allows the coolant to flow. (Obviously I know nothing about fridges.)

Question 1. I assume if if look long enough I can find a replacement part, yes? This may be a 30 year old fridge.

Question 2. Can this part be unscrewed from the connection and replaced by me without all the coolant leaking out? If no, then do I need to get a fridge tech to capture all the coolant before swapping this out?

Thanks for the help folks!

[Pitchondesign]

Originally Posted by Calypso52

Our fridge is a champ. Runs a fridge and separate freezer. Cold plates.
The thermostat has failed on the fridge side. All is normal on the freezer side. For the past few days, I have had to turn the analog knob higher to get it to turn on. Today, nothing. Stuck my head down in there and it looks like the copper (wire? thin tube?) runs from the dial to an item that connects to the coolant line. Some how the mechanism expands and contracts with temperature and allows the coolant to flow. (Obviously I know nothing about fridges.)

Question 1. I assume if if look long enough I can find a replacement part, yes? This may be a 30 year old fridge.

Question 2. Can this part be unscrewed from the connection and replaced by me without all the coolant leaking out? If no, then do I need to get a fridge tech to capture all the coolant before swapping this out?

Thanks for the help folks!

I have three Grunert systems on my boat, about 20 years old, but much the same as yours. There are three "connections" off the analogue thermostat. There are two wires, which are 12v control wires which go to the compressor controller. The other connection is a semi rigid copper line which goes to a sense bulb. The sense bulb is attached to the outside of the refrigerant line. When replacing the thermostat, there is no need to remove the refrigerant from the system. When you buy a new assembly, you will get a new rotary thermostat, the two wires, and the semi rigid copper line with the bulb. You want the entire assembly. The thermostat assembly is still available from Grunert. Its an easy DIY. Grunert systems can last a very long time.

[Uncle Bob]

Originally Posted by Pitchondesign

I have three Grunert systems on my boat, about 20 years old, but much the same as yours. There are three "connections" off the analogue thermostat. There are two wires, which are 12v control wires which go to the compressor controller. The other connection is a semi rigid copper line which goes to a sense bulb. The sense bulb is attached to the outside of the refrigerant line. When replacing the thermostat, there is no need to remove the refrigerant from the system. When you buy a new assembly, you will get a new rotary thermostat, the two wires, and the semi rigid copper line with the bulb. You want the entire assembly. The thermostat assembly is still available from Grunert. Its an easy DIY. Grunert systems can last a very long time.

This , or replace it with a digital one that allows a greater range of adjustment, readily available and inexpensive via fleabay.

[sailormed]

Uncle Bob: "This , or replace it with a digital one that allows a greater range of adjustment, readily available and inexpensive via fleabay."

Look for an STC-1000 Digital Temperature Controller, couple of $ only.

[Calypso52]

Great, thanks for the advice guys. I'll have at it!

[Pitchondesign]

If you buy an aftermarket digital thermostat, you will need to get clean 12vdc from somewhere. The 12vdc coming from the controller is really half wave AC. The 12v power supply in the controller is old school transformer with diodes. It works fine with anaolgue components but not with digital. So, the aftermarket digital thermostats do provide better regulation of temperature, they won't play with Grunert controller as is. It is possible to put a few capacitors in the Grunert 12vdc supply so it better approximates a clean voltage, but this requires some electrical knowledge. I have done this on my units and it works and is reliable. I'm not on my boat, so I don't have the specifics.

Or, you could bring clean 12vdc to the digital controller from somewhere on the boat for power, and leave the controller as it. Once again, this requires some electrical knowledge.

Have fun.

[Calypso52]

Thanks for that distinction. Guess I'll stick with analog. Has worked fine all these years.

[Calypso52]

One more question if I may. Will ANY of the "Universal" analog thermostats on Ebay work or does it have to be the $90 Gruenert thermostat?

[Calypso52]

Oh never mind, those are all 110v

[Coolerking]

Assuming you have the eutectic plates, You need a tstat that is designed for an absorbsion system, and is also in the correct range for the plate you are using.
It works by sensing when the plate is 100% frozen, which is usually 15 degrees lower than the target internal temp of the box its cooling.
The plates should have a thin tube attached to one side which is where you slide the sensing tube from the tstat.

[Calypso52]

And this is not urgent as I can just clip the two leads together to bypass the tstat. All is good!