Refi appraisal: does vacancy lower appraisal value?

[Stan C.]

I'm trying to refinance my duplex, they should call in in the appraisal soon. But suddenly one of the tenants moved out and one unit is currently vacant. Will the appraisal likely lower the value because of the vacancy?  

It would be best not to delay the refi process for many reasons, but if vacancy will lower the value then maybe I should wait... 

Do appraisal officers lower (partially) vacant home's values?