Yes, if you expect a refund then you don't have to pay any income tax due with Form 2350 and you can write $0 or just leave blank. This is because an extension is only an extension of time to file your return, not pay your income tax due.
If you want to, you can use the TurboTax TaxCaster to help estimate if you would have any tax due. But, if you are confident that you will receive a refund, then its not necessary.
https://turbotax.intuit.com/tax-tools/calculators/taxcaster/
