How do i know the capacity of my air con model wsh-128BA

You shouldn't need the manual. There should be an aluminum label on the A/C unit somewhere that says:
VAC: 220
Amps: 16.5 (or some other number)
There will be other numbers as well indicating cooling capacity. You don't need those.
A technician will know what the wattage is based on the two numbers discussed above.

What is the make and model of your aircon

No make or model is visible in your post

You need R134-a refrigerant with PAG oil for your HVAC system (part number F7AZ-19589-DA) . The capacity is as follows:

With auxiliary climate control:

64 oz R134-a refrigerant
13 oz PAG oil

Without auxiliary climate control:

44 oz R134-a refrigerant
9 oz PAG oil

An air conditioner is an appliance that draws a fair amount of current. It would have to be a large generator to run an air con. Does the generator run smaller appliances like a jug for instance. If it does this means that it is working okay, it just can't handle the capacity of an air con.

Lift up air filter cover should find emergency/manual mode botton there.

Capacity which normaly known as Horse Power
or RA rating

The voltage input
Ampere ratings
voltage phase ex. (single phase or three phase)

Type: Split type

since it is split type there are several classification(wall mounted, foor mounted or ceiling mounted)

hi.you should have a sticker under the indoor unit head unit or on the side.

model no
capacity of a/c
need to solve yr problem