My a/c quit working. the compressor is ok. the a/c main fuse is ok. electrical current is not delivered to the main fuse

Fuses blow and breakers trip out - if your compressor blows the breaker it is unusual and spells big trouble. It would have been helpful if you had mentioned whether it was the RCD (or ELCB) or the MCB that was tripping out.

The earlier version of the RCD which is the ELCB detects current escaping down the ground wire indicating a fault. The RCD compares the current entering the circuit with the returning current and will trip if the two aren't identical, again indicating a potentially serious fault.

The MCB or micro circuit breaker is a device that replaced the old fashioned fuse and is in effect a resettable fuse and like a fuse it trips with both a slow overload and a short circuit, though in the case of a slow overload they are less forgiving than a fuse.

I assume it is the MCB that is tripping out when the compressor motor starts to work harder as the air tank approaches cut off pressure?
An electric motor working hard demands far more current than a motor running free and the harder it works the more current it demands.

I speculate your problem is the circuit you have connected your compressor to is incapable of supplying enough current to power it efficiently. I think if you use a supply that is protected by at least a 15 amp MCB (preferably 20 amp) it will be ok, though it must be considered once up to pressure the motor switches off and restarts when the pressure drops - that restart under load has a huge current demand that requires a good supply with minimal volt drop so if an extension lead is being used it should be as short as possible and as heavy duty as possible...

fuses blow because the current flow is in excess of the fuse rating and that is normally from a dead short in the circuit after the fuse
I suspect that the ac compressor rely is faulty and I would start looking in that area

the clutch on the air compressor coil is proably burnt out. disconnect electrical plug at end of air compressor and supply current direct from battery to see if clutch engages, if it does not, change thecoil clutch switch.

If all fuses are ok then check wiring to fan and compressor both, if wiring is also ok and current is passed till the terminals then you have two problems, one the magnet forming coil on the compressor head is burnt, you have to replace or get it repaired. second your fan itself needs checking.

Check battery connections with a meter.

In the engine bay, there is a set of fuses by the battery. Pop open the fuse panel. There should be a set of relays. Check in your manual under "Roadside Emergenies" for the relays and you will find one for the A/C Compressor. The compressor normally checks out fine, it is a common problem that the relay goes bad. Swap the relay with a new one and you should be golden!

my first gess is the switch

Probably the electric clutch of the compressor is not working. This is the part that uses the power generated from the drive belt to drive the compressor. Normally if this is working, you would hear a sound in the engine compartment once you turn on the ac. Otherwise you may have only the AC blower spinning. If they check out OK, the thermostat may not be working. Your AC will not engage because it may be getting the wrong signal thermostat.

yes there is a fuse for your compressor check under the hood or under the dash

on the passenger side inside the wheel well there is a high current relay for the air compressor it is a silver metal relay assy 4 wire plug two smaller wire are the relay power two larger wires are compressor feed. if you jump the two larger wires and the compressor works check the smaller wires for power and ground if ok the relay is bad. usually these relays go bad due to compressor drawing high current and usually need to be replaced