DIY: Digital thermostat. Cooling down excessive fridge’s heat.


Digital thermostat switch relay 12V
XH-W1209

Programmable digital thermostat XH-W1209 and 12V (6x6cm, rated 0.25A, consumes 0.15A) cooler fan to chill down the heat from fridge radiator at it back.

DISADVANTAGE: noisy (unless replaced with low RPM and bigger installed flat at the back);

Independent relay. Programmable on-off-on, delay settings, calibration 0.1°C, range settings, display settings.

Thermo-sensor placed at the back of the radiator. Set to temperature working range: 8°C. Once temperature reached 40°C - fan is ON and when temperature drops to 32°C - fan is OFF.

Little simple system, to speed up fridge cooling, in order to save some energy and move out excessive heat.

Schematic connection

12VDC, connected ground together with fan, common positive to relay, relay output back to the fan.

Observations: radiator size is approx 50x90cm (little compressor fridge with freezer). Fridge back is ~4cm off the wall. When ambient temperature is 22°C, to cool down from 40°C to 32°C takes ~80sec. of working fan.; fridge will heat back to 40°C in ~120sec.

XH-W1209 seven programmable settings:

P0 (Heating or Cooling) – to set the controller operating mode, C-cooling, H-heating. Setting the cooling temperature control (C) will activate the relay when the temperature drops to the setpoint. If you set the heating temperature regulator (H) the relay will be activated when the temperature rises to the set point.
P1 (Hysteresis) – Sets how much the threshold temperature must be exceeded before intervening; for example if you set P1 to 1 ° C and the desired temperature to 20 ° C, the relay will be deactivated at 21 ° C (20 ° C + 1 ° C). The relay reactivates when the temperature drops to 20 ° C.
P2 (Upper temperature limit) – You can set a maximum temperature limit, lower than +110 degrees.
P3 (Lower Temperature Limit) – You can set a lower temperature limit above -50 degrees.
P4 (Calibration) – If you don’t have a certified thermometer, leave the value at 0C. Calibration allows you to adjust the temperature in 0.1 increments
P5 (Intervention delay) – In this step, the intervention delay of the relay is set. If you set 1 minute the relay is activated up to one minute after reaching the set temperature.
P6 (High temperature alarm) – Initially not active, if this alarm is activated the display will no longer show the current temperature but only the characters — when the set threshold is exceeded.