Converting Mechanical Thermostat With Digital Temperature Controller

Window type aircon could be a durable household product, but the thermostat not function properly as times go by, when I found the controller I thought it could be replaced the mechanical thermostat. My idea is not breaking the aircon, just replace the thermostat.

This device has a thermal sensor to detect the temperature change, first select the desired lower bound temperature (i.e. 24 C), if the ambient temperature higher the preset, the on board relay triggered and switch on the compressor, when the detected temperature goes the lower bound the the compressor switch off automatically, once the temperature goes up the higher bound (presetable), the compressor works again, so the aircon only function depended on the detected temperature change.

The controller needs additional power, I bought a small power adapter (12V ??mA), break it and connect main line lead to the AC power plug of the aircon. The controller has an on board relay to drive the on-off of external applicants, it told the rating up the 10A, but I need the control the aircon compressor runs on AC, and not want AC runs on the circuit board, to play safe, I bought another relay which could hold 16A current suitable of 0.75HP aircon, so the AC is completely isolated (check on the schematic).

I connected thick wires to the contacts point of the relay, soldered a copper tab to plug into the thermostat connector lug, wrap up the relay and ready to stuff into the aircon.

With the aircon panel removed, pull out half of the inner unit, this could be the hardest work in this instructable (some model type may not need to do so), pull out the auto swing connector, dismount the power box in lower right side, open the box and remove the thermostat switch. stuff the relay into the power box and reconnect the tab and lug, run the wires through the hole, the sensor lead, the power lead and the relay lead, fixed the electronic sensor in front of the condenser, closed the box the fall back the AC, connected and fixed the controller over the hole of the thermostat and ready test.

The controller has three setting button, SET, + and - , push once the set button preset the lower bound temperature, means that when lower temperature reached, it will cut off the compressor, there are other hidden settings needed to push the SET button several seconds, the display changed from P0 to P6, press + or - to P1, press SET to select. default setting is 2 degress (Celius) deviation, which means that the lower and upper bound temperature deviation is 2 degree (you can only preset the lower bound), press + or - to change, I changed 1 degree, press SET to accept.

The next setting not so important but is good to use, change to P5 and press SET, this set the delayed start in 0-10 min, means that when aircon power on the compressor starts after the delayed min, if other than 0 min, only fan worked, I set 1 min, the compressor will switch on after 1 min, this only effect on power up but not the switch control function.

To return the factory default setting, press + and - both and power on the controller.

As the controller has digital readout, I can easily note the current air temperature, and give a better control over the mechanical thermostat, most of the time the thermostat hang up in the dawn and need to adjust it again and again. The next thing to note is how the electric fee be affected, as I have not break down the aircon for modification, everything can be fall back.