ac doin crazy stuff

[cobradude360]

ok i hav a 92 merc grand marquis ls and when i hav tha ac on and hit about 45mph the vaulves in the dash that controll were the air comes out of goes craz it will be coming out the defroster onthop the dash then on the floor then back to the reg vents it also does it when traveling through mountains were the throttle is going up and down which changes air flow so yea the trip to kentuckey was fun with the air on so if ne 1 can help that would b great thans for the help in advanced

[Samurai0]

Hmmm,

You say the vacuum valves that control the airflow, all open up at the same time?

[cobradude360]

no what they do is alternat but there never open at the same time like the top dash defrosters will b on for as long as 5 min the the floor vents will b open for 5 sec then the middle dash vents will stay open till the throttle plat moves but there never open all at the same time

[fredjacksonsan]

Funky. Sounds like it might be a control module of some sort. I'm not an under dash guy, but seems there'd be something to tell the vents to open/close and when. I'd check to see if your local parts guy has heard of the problem, maybe he can point you in the right direction - or to a FoMoCo mechanic that knows.

[Samurai0]

Not sure about how the porting of the vents are controlled within a '92 mgm, but in an '87 everything is mechanical vacuum ductwork.
And looks new to this day.

My guess is that you have Automatic Climate Control, and the cabin temperature sensor may be shutting the airflow off prematurely.

[corey6135]

I have an 89 mgm and I just found that I had two broken vac lines under the hood. the man that sold it to me said the air did not work and I had a neighbor who helped me trace the lines and we put new connectors on them and YEAH BABY...ICE COLD AIR!!