2003 Mercury Grand Marquis Q&A

2003 Mercury Grand Marquis Question: Why does the A/C change modes, from panel to defrost all on it's own?

At idle A/C blows through the panel. As I roll down the road the A/C will start blowing out the defrost all on it's own. WHY?!?!? -
Answer 1
loss of vac to controller. ck vac lines under hood for cracks or breaks. if there ok ck under dash if unable to find have ssmoke test done to determine leaks -