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? think

Stronger together