In an effort to convert a fridge freezer into something to age cheese (Electronic temp and humidity control) I'm trying to understand the following circuit diagram Fridge Freezer circuit diagram

I'm trying to work out what the "Compartment Heater" and "Compensating Thermo" are. Following the colors, the compensating thermo is inside a terminal box which is subjected to external room temperature. The back cover is not removable from the fridge without damaging the rear cover so I'm uable to find out where the Orange and Gray wires go.

It's definitely not part of the cyclic defrost system (which I plan on keeping). My intention is to cut a vent between fridge and freezer compartments and fan force the air (so the entire unit is at one temperature) and use a digital temp controller, am I right in assuming I should isolate/disconnect this heater regardless of where it is and what it does?

Edit: The cooling coil is in the freezer (fan forced) and the thermostat is in the fridge. The "Compensating Thermo" says "JP3 17" on it.

  • It's likely that the freezer already vents into the fridge, but there's a temperature controlled damper to prevent the fridge from getting too cold.
    – Tester101
    Jan 12, 2016 at 0:38
  • Yes @Tester101, freezer vents into the fridge but the electro mechanical thermostat is in the fridge. I'm still wondering where the compartment heater is and what it does
    – John
    Jan 12, 2016 at 0:47
  • I'd probably leave it intact, given that there is a separate defrost heater. This link gives a good explanation of some different types of heaters you'll find in refrigerators - other than defrost it looks like controlling condensation and making the compressor cycle shorter.
    – Comintern
    Jan 12, 2016 at 23:56

2 Answers 2


The defrost heater is clearly marked in the diagram, so it is extremely unlikely the "compartment heater" is used for defrosting. Most probably the compartment heater is for what used to be known as the "butter keeper" compartment, which maintains a slightly warmer temp than the rest of the fridge so that butter is not rock hard when you want to use it without waiting for it to soften after taking it out. The "compensating thermo" would be used to generate the right amount of heat to keep the compartment at the ideal softened butter temp regardless of what the main fridge temp is set to.

  • Hi! I edited out the part of your post that was addressing the other answer. Answers here should generally stand on their own. Please see the tour for a quick overview of how this site works and How to Answer for what we expect in an answer. Welcome to the site!
    – Niall C.
    Jun 5, 2018 at 0:16

The "compartment heater" is most probably used for defrosting the freezer section. The "compensating thermo" ,I would guess, is an exterior thermostat that will make adjustments to the appliances' interior temperature if the ambient air goes past a pre-determined setting.

If you are looking to modify the appliance so that both freezer and lower section will be equal in temperature couldn't you set the thermostat(s) to the same setting?

But I think you are correct in that the "heater" should be disconnected or removed for a steady temperature setting.

Not the answer you're looking for? Browse other questions tagged or ask your own question.