Well fellas, I have checked and tested everything I know to on these systems. I have no Max A/C and we need it for this Texas heat. I have normal A/C, but it's having a hard time keeping up just idling. When the Max as working, it would freeze you out! Here's rundown.

I repaired the white line last year when it went out and its been fine since. It quit working about a week ago and I have not been able to get it back. I checked that line all the way to the firewall and it seems good. I pulled the control panel and all looks ok behind it as far as connections. I followed the line under the dash as far as I can see, but it looks all good, not rotted,and very pliable. I can't imagine it just developed a hole all of the sudden when its in good shape.

Aaron mentioned a vacuum switch, but I am not 100% sure where it's located. It looks like the unit behind the control panel is not removable without breaking something. The valve under the dash quit working first and I only had defrost. I zip tied that open just to keep air coming out of the vents and not the windshield. It's the valve that the blue line goes to.

Help!! LOL Seriously, any input on this is greatly appreciate. I am at a loss from here.

 

The part I am referring to under the dash and the hood (there's two of them) is called the "blend door actuator" on Rockauto. I am wondering what the possibility is that this is bad? Anyone else had to replace these?

 

I recently installed this kit:

http://www.dieselsite.com/maxacassis...4-200373l.aspx

Now it blows so cold I sometimes have to switch to "Normal" for a while then back to "Max".
While installing it I also noticed the white vacuum line needed repair. The function of the valve that controls the blend door can be seen by switching between normal and max. The valve is at the passenger side firewall in engine compartment on mine.
Hope I'm on the right subject.

 

This is a consideration, but my Max A/C is not engaging at all. I need to get the vacuum issue resolved first. Thanks for this info though! I will definitely look into it. Seems to be a must have

 

Are you sure you're getting vacuum to the HVAC from the vac pump at all? When you don't, it "defaults" to defrost (windshield).

 

I'm not sure. That's where I am a little lost. Where do I start? Something is amiss if neither actuator is working. Does it have something to do with the unit on the driver side fender that the vacuum pump hose goes to?

 

Did you say you checked the valve near the pax side firewall? A white vac hose runs to it and that valve operates when switched from "OFF" or "MAX" to any other position.

 

yeah, that valve is good AFAIK. It seems the switch might be bad because both valves quit working at the same time which is suspect to me.

 

Seems to be a day for OBS guys to have issues. In short, I followed each line from the vacuum switch on the drivers side fender. I found the black line going to the air distribution box split in half! I did not have any replacement line, so I used a butt splice and heat shrink to repair and now both door actuators work! So, the white line has been repaired as well as the black line. The white line causes Max A/C issues while the black line causes both issues with vent AND Max A/C. Hope this helps someone down the road.

 

Actually, I think the black line is for "everything" in the HVAC, so when it goes down, that's what defaults it to defrost. Those lines are made out of brittleite unobtanium; what possessed Ford to use that material rather than real live vacuum lines (maybe in a conduit where they pass through the firewall, etc), who knows. (Guess it's the same thing that possessed them to use rag joint steering and vacuum for HVAC controls in the first place....).

 

I agree on the black line. That's what I said when it does vent as well as max just meaning it controls everything. Good lesson learned for me today. I'll eventually replace them or just fix the bad spots with better material like I did this afternoon. Thanks for your help. Your previous post got me thinking and looking more, so I found the issue.

 

Glad you got it fixed.
Do a search for AC mod. It has been discussed on here once before about how to make the max ac better. I believe it uses a valve from a ford ranger and is cheaper than the diesel site kit.

 

I'll check it out. Thanks! This sounds like something that is much needed in hotter climates.

 

Couldn't you just put a valve in the line going to the heater core, like the big trucks have?

 

Phil, I think that's what the kit consists of. I have no idea, but from looking at the one on Diesel Site, it seems that's what they do.