park release works...also vac source is good..can find no leaks...while driving it will just switch to defrost..and later go back to ac vents..so i am thinkin what tells it to switch..back n forth..with out commands from ac control head?(I think the partial vacuum setup was still used in the 1999s......)
Check the vacuum line from the passenger end of the intake manifold to the firewall and into the cabin/HVAC stack.
Does your parking brake auto release work? If not, it's a vacuum leak somewhere.
yes i get that..just sitting in park it will do it...gonna check the vac res..under the fender..so far i found no vac prob...till tomoro...thanx muchyou - the MODE is vacuum controlled -
and when you loose vacuum DEFROST is the default position -
long hard acceleration dumps vacuum -
coasting/deceleration develops the highest vacuum -