WARNING: This text is addressed to electrical engineering professionals.Electricity is very dangerous and can kill you. If you decide to follow the steps below, it's on your own responsibility and i'm not responsible for and damage that may be caused to you by following these steps.
In order to convert your mechanical relay temperature controller to an improved SSR temp. controller, follow these steps:
Open the controller by removing the front side of the sticker, and pushing in the little bumps that keep the front panel in place.
Here is the controller taken outside of its box.
Here you can see the two relays. The right relay is used for cooling and the left one is for heating.
If you look on the bottom of the PCB, you will see the weldings of the relays. Pins 1 and 2 are connected to the coil of the relay, and pins 3, 4 are connected to the switch.
Use a soldering iron to carefully remove the relays.
This is the bottom side after the relays were removed.
The relay is triggered by a 14V voltage in pins 1 and 2. Connect pin 1 to pin 3, and pin 2 to pin 4.
This way, we tunnel the 14V directly to the connections 7 and 8 of the controller.
Here you can see the wiring of the heating relay. Now, when the controller triggers the relay, it actually will set a 14V voltage in connections 7 and 8 of the controller.
Here is a photo of the top of the PCB with the relays removed.
Just FYI, this is the controller's power supply.
Now it's time to put everything together. Gently put the controller back into its box and push to hear the click.
Use a voltmeter to check your work. When the controller turns the cooling element on, you should have 14V on pins 7 and 8.
Check the heating element similarly by measuring the voltage on pins 5 and 6.
Change the markings on the controller's label.
Now connect the 14V pins to an SSR. I recommend using a 40A SSR.
A SSR relay has 4 pins. Pins 3,4 are the "input" or "trigger" pins. Wire pin 3 of the SSR to pin 7
of the controller. Wire pin 4 of the SSR to pin 8 of the controller.
The brown wires in the photo are the 14V wires.
This is the complete wiring diagram (the text in the purple square means "Fermentation Fridge").
And this is the modified, improved controller, which is very reliable and extremely cheap.