International 9900 Fan turning on a lot

You could be low on freon then.

 

It could also be dirty cab air filters, reduced air flow across the evaporator will cause higher pressure.

 

Run a coat hanger up the drain tube if you're not running water out the drain

 

Was your air conditioning working properly before you added more to it? Is your air conditioning working properly since you added more?

I don't know anything about those gauges that come with the cans but I think if you put too much refrigerant into your system it will cause a higher pressure and make your fan come on more often.