So I’m pretty sure this is a vacuum issue, and I’m looking for opinions on how I can reasonably fix it. So, a while back I noticed some intermittent power issues when I would hit steep grades, nothing crazy, but definitely noticeable that I was down on power. Also, the ac vents would switch to the defrost vents no matter if the ac was off or on, from what I understand that is the default setting of the system so when you lose vacuum the vents switch to that. I wasn’t in a place to test what was actually leaking but i was pretty sure it was the AC controls because I’ve had numerous leaks from that system and just fix them every time they show up, but the last time I just replace all of the 1/8" vacuum lines in the engine bay along with their fittings/joints to make sure there would be no more leaks. so i pulled over and disconnected the vacuum line that ran to the source of the AC system. Im not sure if it’s the same in all of the ram vans (I have the 5.9L Magnum) but there is a port on the passenger side that comes out and has a check valve that runs into a splitter to split the line in 2 directions, one to the cruise control and vacuum reservoir, and the other is the source line to the AC controls, so I unplugged the AC controls and capped the splitter so the cruise control system still worked, I figured this would tell me is the leak was from the AC system or elsewhere. Also, the AC lines in my van were bad (they leaked at all the crimps) so I didn’t mind not having the controls connected because I wasn’t using the AC anyway. This did fix my vacuum problem, instantly I could drive up steep grades and stay in 3ed gear and still be able to reach the top without too much speed loss.

So now that I had narrowed it down to the AC controls I started checking all my lines in the engine bay and below the dash, as well as the vacuum seal of the push button block to make sure none of that was leaking, the next step was the actuators. The only 2 I tested were the 2 accessible in the engine bay. When I pulled vacuum from the port plug under the dash of the van I narrowed the leak down to one of those 2 actuators. finally i traced it to the blend door actuator, which i was afraid of because i have tried to get one of these before (I thought I broke it in the past, but was wrong that time) and I can’t find new ones anywhere, and the only way to replace it is to disconnect the ac lines that are in the way. So, for a while I just left the AC controls disconnected.

A few weeks later (when it started getting hot lol) I decided I would like AC, and I figured if I was replacing the lines I might as well replace this actuator while I was at it. So, I had the system evacuated so I could start seeing what I needed to do. I decided, since I can’t seem to buy this actuator anywhere, I would try and find a working one from a junk yard. I found one out of a 96 B2500, but it was the same actuator. I tested it with my vacuum gun, and it tested good, held vacuum at both sides and actuated the leaver arm that operates the blend door. so, I pulled it and installed it on my van. After installing that I had some new AC lines made, I installed them, and had the AC system good to go. A few days later I started having power issues again and this time cruise control issues, so I pulled into a parts store parking lot to investigate. and when I vacuum tested the actuator again it would not hold vacuum on the side of the actuator that was towards the front of the vehicle, the back side did still hold vacuum. Also, this was tested on the actuator directly, I tested the line to the actuator independently to make sure it didn’t develop a leak somewhere. While I was troubleshooting, I noticed I did not plug my headlight back into the housing when I reinstalled everything the last time, so the light bulb sat on the vacuum reservoir and melted a hole in it. So, I was leaking vacuum from both the reservoir and the actuator, which explained why I was having cruise control issues this time. As a temporary fix while I waited on a new reservoir to get delivered to a parts store, I just capped the line that went to the reservoir to at least seal that leak, and that made cruise control operate normally again, however I can’t figure out how to fix the actuator leak. I can’t buy a new one, and I cant install another junkyard one without having my ac system evacuated so I can pull the hoses (to drain and refill the system again would probably cost about $200-$300). I added some WD40 inside the actuator to maybe lubricate the rubber seals or anything inside to maybe help it seal, and that did help a little bit, but it still leaks out. The actuator works fine, it pushes and pulls the lever that operated the blend door, but when it’s in the off or max AC positions it would definitely be leaking.

My other question is should the vents switch to the dash under any normal operating conditions? for example, with the reservoir capped, and I’m sure not having a reservoir also has something to do with this, if I’m driving up something like a 10% grade, the system only switches to the dash vents after about 40 seconds. Would this happen on any long uphill run where the engine is under high load? According to the OBDII transmitter that connects to my phone (might not be the most accurate thing in the world but it’s all I had for real time measurements lol) at idle my engine produces about 25 inhg of vacuum at idle, downhill, or general low load scenarios, driving up steep hills for a few seconds its usually around 18-20 inhg, longer uphill drives it drops to about 8-10 inhg. according to my service manual, all the tests on the AC controls should hold 8 inhg with an allowable drop of 3 inhg. so, after driving up long hill I watch the vacuum that the engine is pulling is at about 10inhg for maybe 20 seconds before the vents then switch to the dash. Is this because of the actuator or could it just be that because i didn’t have the reservoir connected it couldn’t hold the vacuum actuators in the right position? Would the vents switch anyway after running at lower vacuum pressures for a while even with the reservoir to help? Or should it switch to the dash vent under no driving circumstances?

I’m getting the new reservoir today so I’ll be able to do some more testing, but I wanted to see if anyone has ideas for making this actuator not leak anymore.

 

Without a vacuum reservoir, any time the engine is under a good load, (low vacuum) your vents are gonna switch. Also, I think the actuators are DESIGNED to 'leak' some, to facilitate switching modes.

I think the cruise control is supposed to have it's own vacuum feed..... and for the a/c controls, it should be source, check valve, T to the reservoir, then off to the control head......

 

Well, that was a long read so maybe I missed something, but as far as I can tell, you've fixed everything but now you have a hole in the reservoir. Is that the only current issue?

 

The way the feed ran was a from engine to check valve to tee, one line from the tee to another tee behind the headlight that split into cruise control and reservoir, the other line ran to the firewall junction for the AC controls then I side it has a check valve before running into the source port on the vacuum controls.

Yeah sorry for the long read lol, I try to give as much info as I can in the first post rather than slowly answer all the questions that could come up over the course of several replies lol. Basically the question is is there a way to stop the actuator for the blend door from leaking vacuum, and is there a normal operating scenario where the AC vents would default back to the dash vents?

I am installing the new reservoir today so I'll follow up with how things are behaving after that. Also as a side note for anyone who ends up needing a vacuum reservoir in the future, apparently parts stores can't order one when they look up for the ram vans, there's a doorman part number that looks identical but it actually like 4x the size of the stock reservoir. So I went to a junk yard to see if they had any versions of my van or the ram trucks to pull one from and apparently the 80s-90s Econoline vans have the same reservoir. I'm sure many of the vans from that era probably used a very similar if not the same one, but it's another place you could look if you can't find one.

 

Things are apparently different between trucks, and vans. No surprise there. If once you get your reservoir replaced, you still have vent switching issues, might consider installing a second on, somewhere near the a/c control head...... It would at least take longer at low vacuum for them to switch.