I've seen that other members have had the exact same problem maybe someone can help.

My A/C defaults to the defrost setting. All of the other position seem to be O.K. but when A/C is on it goes to the defrost.

I'm baffled, I've gone over every inch of my vacum hoses with alcohol to search out a leak and don't find a thing . My vacum canister maintains its vacum even after a few days of not being driven. I've replaced both check valves that are in the engine compartment' I've spryed carb cleaner over every inch of my manifold and vacum line inches at a time to see if there would be any change in RPM's but nothing happend. I've pulled my dash apart to see if the temp and position control hoses are leaking and everything seems tight.

Is there something else to check? Is there a shure fire way to seek out vacum leaks? Is there a chance that it could be the EVR (electronic vacum regulator)? For now I've wired the vent door open but that's just a short term fix.

 

It's by Ford design that the AC runs when selecting Defrost. I know that is not what you are saying, I think you are walking the dog by the tail. But perhaps I'm just confused. If there is no vacuum the system will default to defrost. Normal. Fix the broken line at the firewall and all will be good.

 

I thought that this might be the problem but I'm still getting vacuum to the control unit. When I set the air flow to locations other than MAX A/C & PNL FLOOR it seems to switch just fine. When on the PNL FLOOR location it will be on that vents and floor and when I accelerate it will switch to the DEFROST. When I have on MAX A/C it will only be on DEFROST. I wondered if it were because of a no vacuum issue but because it is switching to other places there seems to be at least some. My Vacuum Canister seems to be sound.

Could there be some thing wrong with my control panel.
I've heard of using a type (smoker??) to track down vacuum leaks?