Howdy everyone! So I've been driving my 99 ranger 2.5 now for 2 weeks now. Overall I am very impressed and happy with it. Everything seems to be near perfect and in top shape on this truck and I feel like it'll have no problem paying me back.

I've recently noticed, however, that whenever I start up a hill with the climate control on, it shifts from whatever I set it to, to the defrost vents. It returns to the vents I set it to after I crest the hill, and doesn't change vents if I don't drive over hills. I live in a hilly area so that's not convenient. And with summer around the corner, I want this solved.

I thought it might be an actuator going bad because I know that's a down side on a lot of FoMoCo vehicles. But I've never seen it be caused by a hill, so I don't wanna throw parts at it without y'all's oppinion.

Thanks in advance

 

Maybe a vacuum leak in the control system. When we climb a hill we have to open the throttle & intake vacuum drops. So does it act out if you downshift to keep vacuum up????
If so, inspect the AC control system rubber vacuum lines & connections for a dry rotted, cracked line or connection, or loose connection from a soft hose. If they look ok, hook up your mighty vac, pull a vacuum on the AC control vacuum feed line at its firewall connection & see if it'll hold a vacuum. If it won't, light up your favorite smoke & blow a big puff into the system vacuum feed line & look for leak signs.
Some thoughts for pondering, let us know what you find.

 

Either the vacuum reservoir is defective or the check valve is defective. The reservoir may have the check valve built-in, or you may have a separate check valve between the engine manifold and the rest of the vacuum lines.
As you climb a hill, the manifold vacuum drops, allowing the "mode" vacuum motor/actuator to move by spring load to its default, defrost mode.
You can buy a check valve and put it in the vacuum line leading from the intake, or find the orignal or the reservoir itself.
tom

 

Thanks. I'll give these things a look when I get off work today.

 

So I looked under the hood there's a dry rotted and cracked hose from the valve cover to the intake manifold that I'm sure needs replacing. But is this the one that should fix my problem?

 

Not likely as any hose to the valve cover would not be connected to the vacuum lines that operate the mode flap.
I think if you follow vacuum lines from the manifold, you will find a distribution manifold on the firewall. It would be a spot for all the 'other' vacuum lines to get vacuum, such as the power brake booster, cruise control, parking brake release, and HVAC.
The reservoir will be connected to a line that connects to the brake booster, if equipped, so provide one or two power brake assisted stops if the engine dies. The check valve would be between the manifold and the various vacuum operated devices.
tom

 

^+1 on tomw's ideas


This hose sounds like part of the PCV plumbing & if bad needs to be replaced without delay, as if leaking will corrupt fuel trim, crank case purging & is letting in unfiltered air. I don't know how it might affect what is going on with the A/C vacuum control system. Have you checked the system out as suggested?

 

im in with the same thing. but mine does it at highway speeds. I can let off the gas and increase vac and the ac will change back from defrost to vents. Been needing to deal with it.

 

So where do I put my cigar for this thing to smoke it.

And I'm assuming the check valve is good or the vents would always blow through the defrost. Is that safe to assume?

 

Quote:"And I'm assuming the check valve is good or the vents would always blow through the defrost."

I would not make that assumption, actually the opposite. If the check valve was functioning to keep the vacuum from being dissipated(leaking down) when manifold vacuum fell(high load - low vacuum, idle - high vacuum) while driving at highway speeds, the mode would not change. The check valve leaks, some, and possibly other vacuum lines are causing the vacuum in the HVAC to drop to the level in the manifold, which is less vacuum at higher rpms and under load.
If you pulled a vacuum at idle, and shut down the engine, the check valve should keep that vacuum in the reservoir for some time. If the vacuum lines on the reservoir side of the check valve leak, the vacuum will drop no matter what the check valve does.
The vents would not blow through defrost when the engine is at idle as the manifold vacuum is high, and overcomes the leaks. If the mode slowly flips from A/C or floor to defrost when you accelerate, say onto a freeway, then the check valve is likely leaking, or the vacuum lines/stuff have slow leaks. If the mode switch will not work at all after engine shutdown, then the reservoir is not holding any vacuum due to a check valve dumping the vacuum, or, if it takes time, the vacuum lines/stuff are leaking.
You can isolate and plug to determine which is the case.
tom

 

At this point I wouldn't make any assumptions. With the engine off, disconnect the vacuum feed line from the intake manifold & blow smoke into it & look for leaking lines or fittings.
Did this problem begin suddenly after some event, or slowly over time????
If suddenly, say after a repair, or some maintenance, or the like, go to that area & check vacuum lines, fittings, controls. Good suspects are dry rotted under hood vacuum lines, plastic fittings, control actuators that have rubber vacuum diaphragms, like the brake booster, fuel pulse damper, the in cabin actuators on the heater/ac ducting doors, the firewall mounted vacuum routing manifold, where a number of vacuum lines sprout from. More thoughts for consideration, let us know how it goes.

 

where is the check valve located? I read through, but didnt see mention of a location?

I know my reservoir is on the pass side under the intake box

(mine is a 2004)

 

I've had the truck for a year so and only been driving it for the last 2 weeks. So I haven't a clue what the last 7 owners before my brother have done to it. I know he's recharged the refrigerant but I'm pretty sure that's all he's done to the truck other than tires and a fuel pump. The auto trans shifts really hard but that's a different post.

The vents change instantly to defrost when the truck shuts down or starts a hill. However, I was checking some vacuum lines the other day, and the moment I touched them, I got a hand full of rubber flakes and my hands looked like they would if you wiped them on all 4 tires.

 

Looking in two EVTM manuals, the reservoir does not seem to be connected to the power brake booster in either. That my have been an older 'feature' that is no longer done.
The common thing about the check valve that is that it was connected to the reservoir, and then to the HVAC tube leading to the passenger compartment AND to the line leading to the manifold on the firewall. IOW, it has 3 connections, and is 'in line' between the reservoir and the cab. Back when the reservoir could have been mistaken for a HI-C juice can, but now they are blow molded, and some are spherical, just a plastic ball with vacuum line attached.
To find the check valve, follow the reservoir line, the HVAC line or the line between the reservoir and the 'tree' manifold on the firewall. If you are not successful, take some pictures...
tom

 

Ok, in a quick look around, I found a check valve between the intake and the reservoir (mine is the round one). Check valve when sucked on one way allows air through and when the other way will stick to my tongue.

So I guess next step is to pick up some cigs and blow the system with smoke?