AC control knob

[akatagyourit]

Whelp I'm back folks.
Been tinkering with the truck and getting stuff done and fixed. Still having ac issues. I checked and replaced all the broken or possible problematic lines in the engine compartment to the firewall ports. Inside the cab I have max ac, it works, but once I get going to highway speeds it will cut off and go to defrost or just lose all vacuum to the canister to provide defrost. If I put it on AC or Vents only, it goes to only defrost no matter if I'm idling or driving. Now when I put it on AC or Defrost I can hear a vacuum leak in the dash. I pulled the ac control panel out and started the truck up and the selector for vents, ac, max ac etc has a loud hissing noise but I can not pinpoint the location unfortunately, possibly the switch itself? I went junkyard shopping and got some new vacuum lines and such to check and make sure those didn't go bad and 3 sets still provides the same noise and location. I'm thinking its possibly the switch or something is incorrectly setup at this point. I did try a junkyard switch and had the same results so maybe someone can help me out. Attached are the pictures of the location and the item i'm hearing the leak from.

Front Panel

Backside of panel, the closest switch is where I hear the hissing/leak coming from when on vents or ac, barely noticable on max ac.

Switch removed from panel

 

[RonD]

The vent positions are control by vacuum "motors" like a solenoid but uses vacuum instead of electricity.

You have a broken vacuum line or leaking "motor".

Defrost vent is default position, so OFF or low/no vacuum = defrost vent

AC or MAX AC difference is only a vacuum "motor" vent door, AC pulls in fresh air from outside, MAX AC closed the fresh air vent and pulls already cooled air from inside the cab, recirculates cab air.

This is the general layout of the vacuum motors: http://www.ford-trucks.com/forums/attachment.php?attachmentid=517&stc=1

If you can hear the leak then it should be possible to track it down.

 

[akatagyourit]

The vent positions are control by vacuum "motors" like a solenoid but uses vacuum instead of electricity.

You have a broken vacuum line or leaking "motor".

Defrost vent is default position, so OFF or low/no vacuum = defrost vent

AC or MAX AC difference is only a vacuum "motor" vent door, AC pulls in fresh air from outside, MAX AC closed the fresh air vent and pulls already cooled air from inside the cab, recirculates cab air.

This is the general layout of the vacuum motors: http://www.ford-trucks.com/forums/attachment.php?attachmentid=517&stc=1

If you can hear the leak then it should be possible to track it down.

Yup and i've looked that diagram over numerous times. Like I said I get air out the vents on max ac only. On AC and vents I get nothing, only defrost and floor. It does sound like a vacuum leak on the back side of this switch. I'm kinda at a loss for what to look for now as the red line controls location flow and works for max ac, but when put on ac and vent it doesn't. Guess the next trick is to disconnect each color from the canister and see if its getting vacuum when it shouldn't then?

 

[RonD]

Each line on the back of control switch should be air tight, so get a vacuum hose that fits onto that size hose then remove each one put vacuum hose on it and suck on it.
If it doesn't hold vacuum then that's the line you need to trace.
You should also hear the vacuum motor moving, and vent doors changing, when sucking on a line, if it is working

The Black line from engine bay is the source so won't hold vacuum, but you already know that one is working.

 

[akatagyourit]

Each line on the back of control switch should be air tight, so get a vacuum hose that fits onto that size hose then remove each one put vacuum hose on it and suck on it.
If it doesn't hold vacuum then that's the line you need to trace.
You should also hear the vacuum motor moving, and vent doors changing, when sucking on a line, if it is working

The Black line from engine bay is the source so won't hold vacuum, but you already know that one is working.

You sir are a genious and probably just solved it all. The white line is the source line from the vacuum ball or at least thats the way it was when I bought this vehicle or I screwed it up when I was replacing the gray line to the heater bypass valve i'm assuming it is? Anyways fixed that and all the vent controls work fine now so thats great, but back to problem 1 of the recirc line wasn't working. Very little vacuum on the line. Plugged the bypass valve part and did a hand vacuum pump test from the selector switch on the white line and manually plugging the port on the recirc valve was able to hand pump to 25 inHG, plugged the recirc valve back up and ran the line out to the engine compartment and manually plugged the heater valve and pumped samething. Hooked vacuum pump up to heater valve, can't hold a vacuum to save its life. I'm assuming the diaphram on it is bad. Soooo when the car is on max ac it provides vacuum to this device to prevent hot coolant to the heater core? If thats correct then i'll need to replace it, but I temporarily plugged the hose to it with a cap and left it disconnected. Everything working fine now.

Ron thank you for that line regarding the black line, otherwise i'd be chasing this issue forever........ next up, clutch and slave replacement.

 

[RonD]

Good work

Thanks for the thanks and updating the thread as to the fix