thanks, i hope so, its an old fridge, do you know how can i calculate this RC circuit ?
You need to know at least the current draw of the compressor and the SSR commutating dV/dT rating. See pages 12-13 of http://www.fairchildsemi.com/an/AN/AN-3008.pdf
. Or buy an SSR with built-in snubber.
also, i have a fluorescent lamp near the arduino, when i turn it on, the lcd shows garbage for a while, should i put a capacitor in the SSR input to prevent any possible arduino switch by interference ?
A capacitor across the SSR input isn't likely to make any difference, but may overload the Arduino when the pin switches state. It would be better to find out why the lcd is showing garbage. How are you powering the Arduino and LCD? Does the problem still occur if you power it from a 9v battery connected to the barrel jack? How close does the lamp need to be to make the problem occur?