Filax 2 Transfer switch won't allow air conditioner to start

I have a 700ah lfp battery and Victron 12/3000-120/16 multiplus in my car.
I have a 200ah lfp battery and a Victron 12/500 inverter in my caravan.
I have connected an electro-mechanical transfer switch in my caravan. The 15a socket connects to the priority input and the 500va inverter connects to the alternate input. This way my caravan sockets are all live.
If I need more power than the 500va inverter can output I connect the output of the multplus to the 15a socket on my caravan. I can then run my soft start air conditioner or my 2000w jug.
Recently I replaced the transfer switch with a Victron Filax 2 transfer switch.Everything still works except for the air conditioner. The jug can draw 180ah and still works. If I plug the multiplus into the grid the air conditioner works. If I connect a cable from the multiplus to the plug of the air conditioner it works. I put the original transfer back in and the air conditioner works.

Sorry for the long question but does anyone have an idea of why the air conditioner won’t work through the Filax2?

I know that you say you have a soft start ac, but the web page and the datasheet for the Filax 2 both state

“The Filax has been designed to switch sensitive loads, such as computers or modern entertainment equipment from one AC source to another. … The Filax is not intended to supply high power household equipment like washing machines or electric motors.

It seems like you have the wrong type of transfer switch.

Thanks for your reply. It certainly looks like I have bought the wrong transfer switch. I looked mainly at the amp rating and thought I would be fine. I would liked to have installed a Multiplus but I don’t have the space to put it. Do you have any advice on what Victron device I can use instead?

The standard Victron transfer switches are 230V only, so not suitable.