The A/C on our 2000 Dodge B350 isn't working correctly.

We were highway driving and the A/C was working fine for over two hours. Then suddenly no cold air -- even though the blower continued to move air into the cabin. A few minutes later the cold air returned. This happened once more time while on the trip.

The second issue: I started driving and turned on vent, NOT the A/C, and very hot air came through the vents, almost as if the temp gauge was turned to heat (it wasn't). I turned on the A/C for a few minutes, then back to vent, and the air flow, while not cool (it was hot outside), matched the outside temp.

I checked all the vacuum hoses under the hood to see if there were any visible holes or nicks, but found nothing.

Any help or advice very welcome.

 

Remove the glove box and you will find the blend door lever and actuator back there. Make sure it's not broken or otherwise moving around.

 

I have concrete experience with vacuum hoses and sometimes their holes/nicks/faults are truly invisible and won't come out of the closet until you're fully warmed up and on the road. A Mighty Vac vacuum tester sometimes won't even elecit that fault.

Like electrical wiring on occasion, sometimes you just gotta' replace the vacuum hoses one by one. Sorry. Call the waaambulance. 8((

 

tjkoko: LOL -- that's exactly NOT what I wanted to hear and just what my mechanic said. Is it a good idea to have him do a "smoke test" to see if there's a leak (or is that the "Mighty Vac vacuum tester" you mentioned)?

From your experience, does the problem sound like a leak -- or could it be a fan clutch or the actuator alloro mentioned...?

@alloro: There's lots of stuff behind the glove box. Can you be more specific about what it is I'm looking for?

 

Stevebass: the problem could be a check valve as is common among earlier models. The smoke test is not to be confused with a Mighty Vac shown at the link that follows. It's a miniature vacuum pump device:

https://www.google.com/search?q=migh...utf-8&oe=utf-8

 

Is the more than one Check Valve? Is it behind the glove box?

 

The manuals for the 1993 and '94 Ram Van don't specify the location of the check valves...pisses me off. On my 1994 there's also a vacuum reservoir (therefore another vacuum hose) located below the passenger's side headlight. This, too, isn't mentioned in my factory repair manuals. Grrrrrrrr.

 

Not to rule any of the other suggestions but first place you might check is what alloro said... behind the glove box, it's easy to pull and check to see if the blend door is operating as it should. Just squeeze the sides in to get past the stopper tabs and the door will flop open to view back there.
You'll see a small motor and wiring going to it (hard to miss) and a small rod connecting it to the vent door in the firewall. Use the control *** to switch between vents giving it time to adjust and see if it seems to work properly or not.
I've only found 2 check valves on my 99, one on the side of the intake like most of us and one that is slightly small under the dash behind the control **** in that mess of spaghetti. This one check valve under the dash (on mine) is in the same line that is connected to the heater water valve then run through firewall and then to the control **** (almost positive on that)


Along with checking the vacuum lines also check any of the rubber elbows connecting the lines to where they install. I've replaced some cracked and dry rotted ones just by following where many of the lines go.

I still haven't solved my own "wild vents" completely... mine still change occasionally going uphill but let off the pedal and they will switch back and always blows cold. One thing I did do is set the temp dial just shy a couple notches of full on cold and it definitely helps prevent the vents switching as much

 

JFloors: I turned on the A/C and slowly cycled it through all of the settings. Each setting worked as it should, but the motor with the rod didn't move. (if I looked at the correct device; image attached).

And nothing else behind the glove box moved.


Arrows pointing to small motor

 

Steve I got it wrong! if you switch the dial between cold and hot then you should see some movement of the blend door opening and closing.

just an after thought regarding the 2nd item of your original post, using the vent setting only and it blowing hot air on a hot day. I can say that mine does pretty much same thing. Morning time and about 70ish the vent will blow about that same but afternoon and over 100 here most days this time of year feels like the heat is set to high