Have you ever seen this unit working properly?
Do the connections on the input side match the incoming mains voltage?
Meanwhile, am I right in saying that the fuses that blow have been F5 (the 12V supply)?
(I'm trying to relate your symptoms to the circuit diagram I have here).
It looks like there are two solid-state relays in there; have you been able to confirm that they are working OK?
Any other clues? Like, does the compressor run continuously?
No error messages?