Fresh air infiltration while in Recirculate Mode

[164inTexas]

Hi
I'm working on a 1995 Alfa 164 LS. I think the problem is that I'm getting external air (fresh air) into the HVAC system when it should be in recicrculating (RECIRC) mode.

I'm looking for some way to test that the airpath through the HVAC system is sealed when the system is set to RECIRC.

When I suspect vaccum leaks / false air in the intake of a car engine I use my smoke testing machine. Unfortunately it uses baby oil to produce its smoke, and that has a disintive aroma, so I can't see using it in a HVAC system.

Is there some kind of perfume free smoke test, that you can use on a car HVAC sytem?

Unlike most Italian cars, the 164 produces reallly good AC, when the system is working. The HVAC system in the 164 shares many parts with the SAAB 9000. I've replaced the heater blend doors with new NOS doors, and the CIRC/RECIRC flap seems to seal tightly, but still I think I'm getting external air into the system.

All assistance welcomed

[ice-n-tropics]

My city water department tests for leaks in the city sewer system with oil mist which has no smell.
Japaneese cars first designed HVAC with 100% recirculation instead of the 15% to 25% outside air (OSA) blend used by the big 3 in the MAX mode. My Ford uses some OSA to prevent gas fumes and has a recall to increase OSA which I've ignored. Alfa historically uses 100% recir before 1990 from my experience.
hotrodac

[GM Tech]

Can't you see the recirc door move? or hear the difference when you command it to move either way? I have also used light weight plastic wrap to see if it clings to recirc screen/filter when it should.....have had a few lack of air flow issues with plastic wraps clinging to the recirc entrance....