a/c vent vacumm issues

[AWDRIVEN1999]

So, lately when I step on the gas the vents will switch from the mid vents to the defrost vents, then when I let off of the gas they will switch back to the mid vents... I'm assuming its a vacuum issue, is there any common fault areas for these? it has the auto climate control system in it.. thanks!!

 

[crunchie_frog]

I do not know about common failures. There is a vacuum line from the front of the intake manifold that snakes over to the passenger side that goes to a vacuum reservoir under the platic lining of the fender. The reservoir has a check valve that should hold the vacuum to the duct controls when accelerating. From the reservoir( looks like a toilet bowl float ball) a line goes back though the firewall and another line goes to the heater control valve. All the inspection of the hoses and reservoir are easiest done with the plastic inner fender removed. A leak in the hoses downstream of the reservoir may could cause your problems or it could be the reservoir or check valve is at fault.

 

[koda2000]

the reason this is happening is that you have a vacuum leak (and it doesn't take much of a leak to have this happen). the defrosters are the default when there is no vacuum. when you step on the gas the engine vacuum drops. your leak can be anywhere and not necessarily having anything to do with the HVAC controls. I had an Explorer that did this and it turned out it was because the PO had used a sheet metal screw to plug an unused port near the vacuum reservoir.

 

[AWDRIVEN1999]

thanks so much, I'm going to tear into this this week ans see what I find...