Rotom is Electric/Ghost and drops its Sub type (ghost)
Mujahid was right Mower is Electric/Grass, Heat is Electric/Fire, Fridge is Electric/Ice, Fan is Electric/Flying and wash is Electric/Water.
In an attempt to explain why it loses its ghost typing:
Rotom the Electric/Ghost Pokemon is made of plasma that has the ability to possess random objects. When it possesses those objects, it looses its ghostly form and gains a physical one.
So when it possesses the Lawn Mower and becomes Mower Rotom, it now has a physical body as well as a new attack, so it replaces the secondary type (Ghost) with a new secondary typing.
Personally I love this. It should have been done the first time, but better late than never I say.
Good news! Now it loses it's Earthquake weakness... the frost forme will be more popular now.
I thought Rotom had Levitate ability even in form change...so it never had weakness to Ground based attacks. If it didn't, then no, it doesn't lose weakness to Earthquake. Heat Rotom is now x4. Washer Rotom is still x2. Fridge Rotom is still x2. Only Mower Rotom and Fan Rotom lose Ground weakness. The former being x1 and the latter being x0.