A/C troubles

A few weeks ago I got a new stereo installed in my 91 XJ and since then my ac blows thru the defrost when I am accelerating but goes back to normal when I am coasting... I know this is a vacuum issue but where? It happens on Max, normal and bi level...

Any help will be greatly appreciated!!!
John

P.S. I'm new to the site and wanted to say Howdy y'all!!!

a vac line popped off. take it back where you got the stereo installed and tell them to fix it.

I do know that there is one vacuum line running into the firewall but I can't see where it goes too... I have taken the stereo out and tried to look in to see if I can see that vacuum line but no dice...

well if it's not leaking there go rent a vacume pressure guage form crapy tire and see if it holds a vacume. Mine does that as well I just let off the gas and it goes back to normal

There is a vacuum line plug on the top of the heater controls. Think it´s four vacuum lines. I´ve popped it off twice now (installing a radio) and had it pop off once on it´s own