Pressure test shows no leak, but coolant reservoir is empty. Where is it going?

What is your question?

My 2010 Focus got a new heater core, thermostat, and water pump 2 months ago. It had been blowing heat on the driver's side, but cold air on the passenger side. Now there is an odor coming through the vents when the heat is on. The coolant reservoir is empty so I figured the odor was antifreeze. The dealership pressure tested it for 3 hours and tells me no leaks. They said they also smell odor but aren't sure it is antifreeze, say it may be exhaust. How do you explain the empty coolant reservoir if there are no leaks? leaks? when the heat is on.

What makes this problem better or worse?

The odor in the car is noticeable when the heat is on.

How long has your 2010 Ford Focus had this problem?

At least a few weeks.