On my 98 Ranger 2.5L I checked my vacuum lines under the hood going to the vacuum reserve ball I couldn't find any breaks. The only line that broke a long time ago was the gray line coming out of the evap box to the heater control valve, which I had to trim and fix with a small diameter hose. Under all acceleration conditions except idling in park the air from the vents defaults to the defrost door. Now I know the blend door could be dead but is there a way to get to it without removing the steering column and entire dash frame? Can you get to it at all if you remove the control head and radio? Or maybe can you get to it if you remove the glovebox? Maybe a vacuum line is broken inside that I can't see. I don't know but it's getting annoying not having ice cold air blow at you when it's 95 degrees and 80% humidity. There's definitely something wrong.

 

Yours is not a blend door issue; it's a vacuum leak. You need to do some vacuum line investigating.

https://www.ford-trucks.com/forums/7...s-on-feet.html

 

I went through the links you posted about the vacuum. I checked my vacuum amplifier ball today as suggested by the link you had posted. I couldn't even get the vacuum pump to go to 15 in/ most I could get to was 10 in/ and it dropped rapidly. I thought it was maybe because the vacuum pump hose was letting it leak out so I changed to the absolute smallest diameter I could get 23/64" and it still wouldn't make it to 15 in/. I still thought it was the vacuum pump hose leaking so I took it off plugged the end and it wasn't. It held. Should I still try another hose? I'm not sure I can find a hose any smaller.

 

Did you pull the climate control module from the dash and check the vacuum line connections back there? Were you able to follow the main supply line from the ball up to the dash and verify its integrity?

Sounds like you tested the reservoir correctly. The failure of the reservoir ("ball") to hold any vacuum at all seems to indicate a bad check valve.

 

I had a similar vacuum leak just after having my alternator replaced. One of the lines feeding into the cannister looped around the back and underside of the alternator and when the tech replaced it, evidently rerouted the line, which came in contact with the exhaust manifold. I noticed a black shiney spot on the manifold which led me to the melted through vacuum line. Once I spliced that, I got the full range of settings through the heater control.

I was preparing to pull the radio, the dash panels to gain access to the controller thinking it could be at the root of the issue, but I was glad to find the melted line and cut my work down by several fold. I exhaustively explored the gray vacuum line that runs through the firewall prior to that, but everything was o.k. there.

My guess: vacuum line issue. Good luck with your diagnosis!!

Kevin

 

The only line I know that broke was the gray line connecting to the heater control valve when I replaced the valve a few years ago. I spliced it with small vacuum hose. I didn't follow any lines into the interior behind the dash because I don't have enough time in the day between having a day off and the next day at work where I can have everything put back together. I could probably pull the radio and control head out and look and see what I can behind there. But I would assume the lines behind the dash should be pretty well insulated from the outside engine temps and so forth. I would assume the problem is under the hood. I went and rechecked the vacuum amplifier ball and couldn't get it to hold a vacuum at all. Is it possible that I can disconnect the lines there, remove the vacuum ball and take it to a shop to verify I'm doing it correct? I wasn't sure which one was the outlet but assumed it was the one going into the interior since the other line is receiving vacuum from the engine. But anyways I tried both fitting just in case and couldn't get a vacuum anywhere. Can you disconnect the hose and put a vacuum fitting in the hose end and apply vacuum to the lines and see if it holds in whatever setting is having the problem?

 

If you disconnect the vac feed line at vac canister and don't feel vac ,check the line where it connects to throttle body or intake manifold. The line might appear intact but must have a hole somewhere along it's length allowing vac to leak.

 

I just checked that. I got feel pretty good vacuum from the hose. I also took out the radio, control head, and glovebox and the vacuum lines from the box to the switch and from the firewall to the vacuum motor all looked just as good as the day they were new. I pushed open on the door to see if I might able to hear any vacuum leaking but nothing. I don't know if that would tell you anything anyway. Is that all the vacuum lines there is? The grey and the black from outside appear to be plastic as these in the interior appear to be silicone. I just need to verify for sure if that vacuum ball is working. I don't trust the vacuum pump enough or the hoses I have. But all I know is it's pretty bad everytime you accelerate it defaults to the defrost vents no matter weather you're going up a grade or not. I think the black wire pulls vacuum from the engine so it's got to be there or the check valve not working at all. I didn't see any signs of breakage on any of the lines. You do get access to see all the vacuum hoses once you drop the glovebox. It might even be possible to change the blend door actuator too with just the glovebox down.

 

If you have a straight vac tee try joining the two lines from vac ball to eliminate it to help rule it out. If no improvement would suspect the vac connection at actuator. Would be particularly suspicious of those hard plastic vac lines as they get brittle and crack enough to leak but may look intact on inspection. You know you have a good vac source at main vac connection so somewhere downstream there is a definite leak. Should be able to hear a hiss at the source of the problem.

 

Well I replaced the vacuum resevoir today with a new one from Ford. It was definitely bad. I heard the check valve rolling around inside the old ball. I went for a short drive and it didn't seem to cure the problem. It still goes to defrost under a load. I tried switching from Max A/C to just A/C mode and it seems that it is ok in A/C mode. However, it's not conclusive because I didn't drive it enough in areas where it was put under a load. I'd love to check the plastic line going through the bottom of the evaporator case under the hood but I can't figure out how to get at them once they go through the firewall. I don't know if you have to take the whole case apart just to see the lines. I'll know more tomorrow when I drive it all day.

 

Are you saying that it only defaults to defrost in MAX A/C mode?

If so, then you need to look at that gray vacuum line (heater control valve) again. And also the white vacuum line (outside recirc door valve) that it tees into.

https://www.ford-trucks.com/forums/a...ntid=517&stc=1

 

Yeah when I drove it today I had it on the regular A/C mode and it didn't default at all, kept the cold air blowing on me all the time. I switched back to the max A/C to check it again and it is defaulting back to defrost so it looks like it only does it on that setting. I know the gray line to the heater valve is the one I repaired with a rubber vacuum line because Ford said you can't get the plastic lines anymore. However, how can I follow it all the way in to the cab because I can't see it anymore when it goes under the evaporator case in the engine compartment. Is that white hose the one accessible when you pop down the glove box?

 

I did some more looking around at the vacuum lines and under the a/c box behind the glove box. I drove home with the glovebox off so I could see what was going on. Well I noticed the door there that you can plainly see and the vacuum motor it goes to didn't move at all in any mode while driving. When I got home I got down close to that vacuum motor and operated it with engine and a/c on and the arm on that motor barely was even moving, almost not even noticeable. I had to use an LED flashlight to see it move. But the door didn't move at all in any position I tried. Does that tell you anything more? I could not pinpoint a vacuum leak from any hose. When is that door suppose to be open? It's the only door you can plainly see when you drop the glovebox. I think it's the recirc door.

 

The recirc door is only supposed to close when MAX/AC mode is chosen.

If it doesn't close in MAX/AC, then that would support the theory that there is a leak in the white and/or gray vacuum line. Alternatively, the recirc door valve could be bad (and leaking vacuum).

 

The recirculate door should only move when you select the Max AC position. It should move and stay in that spot as long as MAX setting is used. Of course it recirculates the air in the cabin and shuts off air intake from outside. It doesn't have any control over where the air exits (floor, dash vents, defrost). That function is controlled by another vac motor. I don't have a diagram to tell you where that vac motor is located. I would assume that the default to defrost would occur in any setting on the HVAC with a leak. Don't understand why your's is doing this only in the MAX setting. Have you inspected the actual HVAC control in dash to see if there is a vac leak at the back where the lines attach?

( Didn't mean to duplicate the advice and didn't see previous post showing the diagram. Rockledge has you covered with helpful information as always)