My AC was charged a few months ago and works great.


What I have noticed is that the mixer/selector **** does not work on following settings...


1. MAX and AC....no difference that I can hear when switching or notice in cooling. Cools fine.


2. When I set to vent, remains coming out at floor.


Off, and AC work fine. Floor seems to be on all the time.


Since it will eventually get cold around here, I need to be able to have selector switch work correctly on all positions..


Where can I start looking or is there a likely culprit?


NOTE: I did notice that the vacuum hose near heater hoses was cracked and I repaired with a section of rubber hose (AC guy noticed this when he notice when he was servicing AC). The diaphragm or valve (near the heater hose connections) appears to work fine (opens/closes) when I suck on vacuum hose (the one I repaired), but doesn't appear to be enough vacuum to open/close the door that the diaphragm/valve operates when connected.


Does this have anything to do with my problem?


Thanks

 

I was told to replace the white vac line up by the passenger side under the hood.

 

MAX AC is just 'recirculate'...
So, the conditioned air is run through again, instead of hot humid air getting one pass through the evaporator coil.

There is a vacuum line that goes IN to the selector that may be broken.
if you don't show vacuum coming out TO the damper actuator, check first the hose that comes from the three way plastic manifold attached to the firewall on the passenger side of center.

 

This one.

 

The first one is the vacuum line I repaired.


The second one is the one I believe you are referring to, correct? If so, what do I do next?


BTW....what do I need to test vacuum lines?


When you say, vacuum to a line you mean SUCTION FROM that item, correct?


Would never be pressurized air coming out of a line going to a switch or a valve?
Thanks

 

I'm talking about the one that appears to be coming from behind the air conditioning lines and goes thru the round check valve.


Yes, I mean -suction- going to, or coming from, a line.
There should be vacuum available whenever the engine is running orif there is a reservoir with a check valve to hold vacuum.

If the engine backfires there will be a pressure wave instead of vacuum, and this can damage seals, diaphragms or blow a line off a fitting somewhere you cannot even see it.
I use my MityVac to test for proper operation and to see if a circuit will hold vacuum.

VERY jealous of how clean your trucks are down in the southwest!

 

The white line going to passenger firewall. Mine did the same thing. Get some vac line and fix. takes 5 mins

 

Thanks.....

So, am I following the the white vacuum line in pic 1 that goes from that valve to somewhere else? I believed I followed it part way and it headed over to driver's side on engine compartment. Where does that white line pick up vacuum from?

 

can someone tell me where in my pics I should look for leaks? Do I need a special vacuum tool to diagnose?

I didn't see any problems with lines under dash (see pics).
For my specific problem, is it the white vacuum line in engine compartment (pic in post above) that I should be focused on, or are there other colors that could also be the problem?







under dash to right of glove box





under dash to left of glove box





under ashtray....some sort of connector where several vacuum lines come together

 

When I had my issue and the vents would only go to defrost mode, it was a hose under the hood that was the culprit.

 

If you lose vacuum to the blend door, it will default to defrost mode. If it's stuck on floor only, I suspect you have something stuck in the blend door holding it in place.

Jason

 

I checked all the hard vacuum lines that went from the passenger side to the driverside up by the egr valve. They lay across the top of the motor and mine were broke in several spots. They were encased with split loom so they were not visible.

 

Here is the vacuum diagram for the selector ****. '92 460 F-series

 

Great diagram. Where did you find?

 

My brother is in vocational auto shop ( I used to be to but that was years ago ) so I have access to Pro Demand online and Mitchell vintage. I used All data at my school but same thing. Feel free to PM if you anything man. we're all here to help each other.