No or little vacuum at the A/C control

[Fordfam93]

Hello all,

I have searched High and low (even under the rug) but I cant find any information under any search that will help me here.

I have a '99 Explorer XLT that cant hold vacuum at the A/C control. I have been wrenching since I could hold a tool, worked as a mechanic for several years. However this one baffles me.

Soo... Heres what im incountering,

Have only owned this truck for a few months, and im finding all its (what you would say its "hick-ups" but the big thing right now is the vacuum supply to the A/C controls. We got the truck in late winter and everything worked fine at the time, but as the temps outside got warmer, the air conditioning system got worse.

At first start up everything is fine untill you apply a load then the A/C controls would defult to defrost untill normal load was restord. That was OK at the time as I figured the A/C condensor and/or radiator was dirty and needed to be cleaned. After inspection of this, I found it clean. Again as time went on and temps got warmer, it got more and more on the decline. Now it tends to stay in this default stat of defrost. I can clearly hear a vacuum leak however the engine runs fine. It almost seamed as though the barometeric pressure and humidity changed the way it operated ( I know this is not the case ). I can clearly hear a vacuum leak around the mid section of the dash area and the same area under the hood (behind the engine, close to the fire wall).

I have looked around to try and find the source oof the leak, but with no luck. I have read other posts about the 4X4 (AWD) not ingaging, and possibly of the same (vacuum leak) problem, but the AWD works fine. looked for diagrams, pictures, anything pertaining to this, and have come up empty.

ANY suggestions, links diagrams (Better then Google) would be helpful!

Thanks you all for your time, and look forward to being of some help to someone in need here as well!

 

[bobflood]

Where the air comes out (defrost, panel or floor) has nothing to do with the "refrigerant" part of the HVAC system (condenser, radiator, compressor, etc). There is a small vacuum line that runs off the intake manifold to a vacuum reservoir (a softball sized plastic ball inside the right front fender liner). I think there is a vacuum check valve around or built in to the reservoir. The vacuum reservoir in turn has a vacuum line that goes thru the firewall into the back of the HVAC control panel. I'm pretty sure that the lines from intake to reservoir to back of banel are black. There are three colored vacuum lines that go from the back of the panel to the various vacuum actuators that control the airflow. The system defaults to defrost when vacuum is lost. Based on your sounds, look for the line where is goes thru the firewall first, but the break could be anywhere. Good luck.