Once finding the Frozen Wrench take it to the Break room and take it to the old rusty sink with warm water inside of it set this item in the sink it will thaw out take the wrench to the Laboratory where you find two maintinence panels and a yoko zombie you take the wrench too the panel on the far right and use it the panel will open revealing a valve which you use on the door that cannot be opened in the same room. Go up the ladder you will be a whole floor higher.