What I expected to be a 15 minute fix became to be an almost 2 hour one. The main reason: the problem was not really related to the safety sensors, but a bad cable which I could not identify the first time. But it was worth changing them anyways as the original safety sensors were really worn out and not installed properly using any brackets at all. This was against code and was like it since I bought the house.
I proceeded to install the new safety sensors, and after ensuring that they were working properly. I installed the brackets 17 inches above the floor. Aligned the sensors and worked perfectly until I faced a new problem.
The garage door has thick horizontal wood bars which were wider than the distance provided by the brackets for installing the safety sensors. It was causing the door to open right when the first wood bar crossed the sensors. This was a big deal as it was not allowing the system to work properly. Seems the reason why the previous owner never installed the brackets in first place.
What I ended up doing was reversing the sensors so they face backwards instead. That was the only way to make them work. This garage door opener system was installed 7 years after the house was built, so my guess is that the wrong model was chosen.
There is always a workaround. The system is working properly now.
