Yeah, getting the manual would be a smart move. I’m looking at one that’s described as an HVAC drive; is one VFD much like another, for our purposes?
Myfordman (Bob) has written an extensive article on VFD's which will likely answer the questions you have.
Induction motor information here
https://drive.google.com/file/d/0B_GZrXNsNxTlQzd6aldlQjJtUDQ/view?usp=sharing
What are you planning on running?
I use cheap ones for a TS and bandsaw.
Some of the fancier ones offer more protection for the motor and the VFD
These things don't like it if the motor bogs down, I learned that the hard way, by being a numpty using a damaged blade.
Luckily my motor was alright, got too hot though, could smell it!
I bought another hundred quid one and was sorted.
I won't be taking the peas again like that.
Some VFD's have parts so you can use a braking resistor for emergency stops.
Some are more suited for spindle work and have all sorts of options, ports, and a big list of parameters for controls by computer.
Some have a fan that runs constantly, although you (probably) could modify any of them
to "shut up" with a little temperature activated switch.
Nice to have on a bandsaw that's plugged in a lot of the time.
3 wire control, (separate start and stop switch) and the cheapo units.
A while back I helping another fella (and myself) with a Far Eastern unit for a TS
He had a similar issue with his start and stop, like I had...
(I just swapped the front panel with the old one on mine)
Seems like a few of the ports for the switches can be faulty.
I was informed on SMC that you can allocate/change a function of these ports
if you wanted emergency stop (if your VFD actually had the components inside for it to work)
Or in this case, changing the function of one of them, so three wire control is possible.
(which is a much safer than a simple toggle switch, i.e "two wire control")
You can do things like make a kick paddle
That could be any of the three little micro ports for a separate start and stop button.
Which would be your start (FOR) which goes into a common (labeled RST on my VFD)
and from that to the stop (DCM)
I couldn't get three wire control to work with the new one, but I have yet to try seeing if I could have a go allocating functions to the ports.
There are much less ports on the new one, and I'm not even sure if it has those parameters available.
This noisy Huanyang was put on the tablesaw, and has a nice eerie hum to it.
The replacement I've hooked up a toggle switch to instead, but I've kept the emergency stops.
This isn't good practice, deffo confusing for someone else not aware!
as I can start the machine by de-latching the push button, as the manual start is always flipped on...
I like having the button under the big table, so got used to using it.
One more thing to beware of is that some sellers are passing off micro sized units with photos of the regular sized units.
I can't imagine them working TBH, how teeny they are.
Get dimensions first, before buying if choosing these.
And lastly be aware that these hold a lethal charge well after being unplugged
Wait until all the juice has drained from the caps before going near those main
input/output terminals, that could take some time.
And make sure that you understand parameters before hitting start.
Many of these are factory preset for high speed spindles which would cook your induction motor.
Bob's write up will answer all about parameters.
the best read up I've ever came across, thanks to him it has opened up a world of machines, which wouldn't be feesable for me otherwise.
Just my 2 cents on the cheap options.
All the best
Tom