It's not entirely true that relays either work or don't. As relay contacts age they become "dirty", so that when the contacts close, sometimes they carry current, sometimes they don't carry current. But swapping the relays is a good test.
Do both fans run when the A/C is on ?
Did both fans run when you swapped the relays ?
Which relays did you swap ?
You can check the compressor with the engine running and A/C on by connecting a wire from the slot in the picture below, to the +ve terminal on the battery.
but DO NOT LEAVE IT LIKE THIS FOR MORE THAN 30 SECONDS, DEFINITELY NO MORE THAN A MINUTE AT THE MOST, AND DO NOT REPEAT AGAIN FOR ANOTHER MINUTE. IF YOU LEAVE IT LIKE THIS WITH THE ENGINE RUNNING YOU MAY OVER PRESSURISE THE SYSTEM. (there is a safety pressure valve in the compressor, but do not rely on it operating)
The other source of the problem could be the pressure switch, the contacts in that might also be intermittent
again, DO NOT LEAVE IT LIKE THIS FOR MORE THAN 30 SECONDS, DEFINITELY NO MORE THAN A MINUTE AT THE MOST, AND DO NOT REPEAT AGAIN FOR ANOTHER MINUTE. IF YOU LEAVE IT LIKE THIS WITH THE ENGINE RUNNING YOU MAY OVER PRESSURISE THE SYSTEM. (there is a safety pressure valve in the compressor, but do not rely on it operating)
edit: when you do either test, also make sure that the temperature is set to "Lo"