A/C TRIPPED BREAKER

check amp draw either bad compressor or fan motor

If it trips the circuit breaker as soon as you turn the FAN on, suspect either a bad fan motor or a failed fan motor start capacitor. If you are able to turn the fan on but the circuit breaker trips as soon as the COMPRESSOR starts, it is possible that the compressor is seized.
If, on the other hand, the unit is tripping a GFCI (Ground Fault Circuit Interrupter) breaker or GFCI utility outlet, it is possible that neutral and hot are reversed at the outlet into which the trailer is plugged (happened to me this year at an RV park).

Want to install split unit aircon in my caravan but see it only has a 16amp breaker, would this be able to run fridge, kettle and aircon at the same time?

I would check thermostat first. Remove compressor wire from thermostat and see if that cures starting by itself.

Check the condensor unit. May be dusty. Clean it. If still problem replace capacitor.

since the fan doesn't run - the compressor heats up and pulls excessive amps and trips the breaker.
99 out of 100 times your fan motor will be bad.
You need to replace the motor.

you have a 'direct short' - most likely the compressor or fan motor.
you could isolate it to one or the other by (be sure all power is off) disconnecting one of them and turning the unit back on.
For example if the fan motor is shorted and you disconnect it - the breaker will hold and not trip and the compressor will come on - which will tell you that you need to replace the fan motor.
If you do this and it still trips the breaker then reconnect the fan motor and disconnect the compressor and try that.
If the breaker holds and the fan motor runs then you know the compressor is shorted.
Note: the fan motor can be replaced with not a lot of trouble depending on how mechanically inclined you are - but the compressor will take a qualified serviceperson.

The breaker tripping when you turn the unit on indicates a 'direct short' and 99 out of a 100 times the short will be either the outside fan motor or the compressor itself. Either way - you will need a qualified serviceperson to diagnose this problem correctly and make the needed repairs.
Best solution is to call AC person.
However, here's a good way you can get it down to either the fan motor or the compressor.
(1) With all power OFF - disconnect the wires to the fan motor
(2) turn on AC unit (a) if breaker trips it means the compressor is probably the shorted component. (b) if breaker DOES NOT trip and the compressor runs - it means the fan motor is shorted.
(3) If breaker tripped with the fan motor disconnected meaning the compressor is probably shorted you can then (with ALL POWER OFF) 'disconnect the wires going to the compressor' and re-connect the fan motor wires. Turn on power - and if fan motor runs (with compressor wires off) you know it's the compressor that is shorted.
After all this you will now know which of the two (compressor or fan motor) is shorted.
If it's the fan motor you can with 'limited mechanical experience' change the motor yourself, but if it's the compressor you will need to call a serviceperson because of the expertise needed to replace the compressor.

Chances are you have a bad breaker or loose wires on the breaker. What size breaker do you have on unit. Heat of the day plus full load on the unit could cause it to trip. Rus

Tripping the circuit breaker means that something is shorted out. A fan motor or the compressor, most likely. Disconnect the compressor or turn the thermostat up so high the compressor doesn't start. If the breaker still trips, the fan motor or its capacitor are the problem. If the breaker stays on, the compressor or its capacitor are causing the problem.