I drive a 93 Bronco and have started having problem with the AC vents inside the cab. When the AC is turn to Max AC after a few minutes air stops blowing out of the vents, If I turn the swith to normal it starts blowing again. I can still hear the fan motor running and the compressor is also working. Unit is on R12.
I have also replaced the vacume control switch, did not fix problem. Looking for help....

 

kind of sounds like the vacuum switch under the dash thats causing your problems. Lay down on the passenger side ans flip the AC switch around to different positions and see how it moves.

 

Thanks will give it a try

 

Change the vacuum switch under to right side and all seem to be working again.

 

I have that Max A/C problem; it cuts off and no air blows out the ven for a few seconds when I accelerate from say 45-65; and then after I settle it I can hear the Max AC "engage" and then the air blows out the vents?

Dutch

 

Dutch I'm still having some what of a problem, will look into vacuum problems on monday and will advise. Larry

 

There is a vacuum canister under the hood that stores vacuum for the AC functions when the engine vacuum is low. Some times they rust or start leaking, causing these sorts of problems.

 

Mine was doing the same thing. The vacuum line just inside the firewall near the heater hoses on the passenger side was rotted. I cut the hole short and replaced the boot from Pep boys I think. Works great now. I think my lines were white in color. Good luck.

 

Must be something in the air, mine started doing this Friday night! I'll check these tips out, see if I can find the problem, and report back as well.

 

Well it now time to check out all vacuum lines starting at the engine. I'll still having the same problem. I also have a complete set of shop manuals and will research it also. Will continue to post if I find something..Larry

 

It looks like I might have found the problem with mine. After researching the manual I found that the Outside Air/ Recirulation Vacuum motor was not working. This is a small
vacuum motor located under the hood right above the heater core. What I found was that the vacuum hose was laying on the fan motor and the bottom side was bad. I went to local parts store and got a short piece of vacuum hose (small inside hole) and used it as a splice and cut the bad section out. The bad section was on the bottom side of the hose and by luck I found it. As of right now all looks and works good in driveway. Will drive to Palm Springs in morning, this will be the true test.
Will post if things change...Larry

 

Must be an epidemic! I have the same problems. Basically, the blower only goes to the defrost vents, A/C or not, but it has flirted with Dutch's symptoms, too.

Here's what I know: Some of the vacuum tubing appears at an engine compartment thru connector near the firewall, behind the air intake snout. There are three lines there: a black/red to/from the vacuum reservoir, which buffers lots of the vacuum system. The third, small black tube comes directly from the intake vacuum connection (ie, the reservoir doesn't affect the A/C-heater controls). Right after the 3-way connector it goes to a thru connector and then disappears down behind the blower. It reappears inside the passenger compartment, where it joins a white tube at a 2-way thru connector. On the other side of that connector it becomes a softer plastic tube and heads, I think, to the vacuum switch in the heater controls. The suck at the 1-way thru connector inside the engine compartment seems strong (when I put my tongue on it). Inside, however, the suck is noticeably weaker. I suspect there's something in the line before it passes through the firewall, because you can suck on the line (disconnected, inside the engine compartment) but you can't blow (the 2-way inside the passenger compartment is disconnected).

So what's behind the firewall in the small black line, could it be faulty, and how the heck do you get at it?

 

The Black line is the main vacuum source for the vacuum switch control on the dash, the white line goes to the out side vacuum control motor which is by the heater core. Under the passager side you will fine a blue line and this controls the passage of air going thru the vents. In the 0ff position and Max AC the vacuum motor by the heater cord must in the positioned so that outside air cannot pass into the evaporator case. I found that this white line was bad on my unit. Their are two other vacuum line leaving the control on the dash, they are Red and Yellow. These to go to the vacuum motor which control the floor/defrost vent. I have a great Diagram which I can scan and post if someone can tell me how. At the present time my problem may be fixed. It did work fine on Friday going to Palm Springs. I will continue to review and help if I can. Larry

 

A problem I once encountered was the vents would be blowing great and then nothing, if you let off the gas for a second it would start blowing again. The problem was the vacuum reservoir was leaking and thus no vacuum so the vacuum motor that controlled the A/C outlet ducts would divert the air to the heater ducts. This problem was especially bad when pulling a long grade where you didn't let off the throttle for a long time. You can see the old Bronco along with my other Fords at
www.michellesfords.com

Michelle

 

According to the diagram under the hood of my '92 E-150 the vacuum reservoir doesn't serve the "A/C" line (the black one leading to the AC/heater control unit that's puzzling me). Maybe other models are different. That's too bad, because I have had michelle's symptoms (until things got worse). I do get suck on the black line while it's inside the engine compartment.
It would be great to have a diagram, Larry, and even better to have a trouble shooting scheme. My Haynes manual is, as my granddaddy would have said, about as worthless as a handfull of sour owl *****.
I'll keep trying to track down the problem, 'cause it's too darn hot to let it go.