Hi Mikael Falkvidd, thank you for reply.
I didn't build any yet, just my garage door safety sensor not working and I am looking for some solutions.

My garage door sensor receiver not works time by time, may because of the winter cold?

I opened the receiver's box and plugged into the connector, the green led is on, disappear after few times open and close test.

Should I buy a set of new sensor or fixable? Or is it OK to exchange the mounting left right side of transmitter and receiver?