Dash AC 98 Roadtrek cycles to hot air

[Kinch]

Dash AC 98 Roadtrek cycles to hot air after driving for a bit

Hi all, I’m having an issue where the AC is working fine (refrigerant is topped off) and the clutch is engaging, cold air is blowing but when I’ve been driving for 5 minutes or so, the dash air switches to only windshield vents and starts to blow hot air.

I’m leaning towards one of the high/low or condenser sensors but I wanted to put the question out there before I start replacing things

Thanks in advance

[rowiebowie]

Probably a vacuum leak or bad blend door actuator. And yes, auto makers were still using vacuum tubes in '2011 on my Chevy Express chassis. How I know is I was tracing where a small tube went under my hood (can't even remember why now). The next time I drove my van I had intermittent loss of dash a/c. When I got home I retraced the tube since that was the only thing I'd done under the hood recently. Well, the tube had come off the vacuum reservoir nipple. It came off so easily, I hadn't even felt it. No clamp, just pushes back into place. So I did and a/c functioned normally.

[Kinch]

Thanks, will check later today

[booster]

Originally Posted by Kinch

Dash AC 98 Roadtrek cycles to hot air after driving for a bit

Hi all, I’m having an issue where the AC is working fine (refrigerant is topped off) and the clutch is engaging, cold air is blowing but when I’ve been driving for 5 minutes or so, the dash air switches to only windshield vents and starts to blow hot air.

I’m leaning towards one of the high/low or condenser sensors but I wanted to put the question out there before I start replacing things

Thanks in advance

It sounds like you might have two things going on, both related to dampers and controls.



Many vehicles put AC dried air to the windshield and heated air to the vents when in defrost, but if the setting of the temp is on the coldest, they both should be cold. That the vent air is hot would seem to indicate the temperature blend damper is also moving or leaking hot enough to warm the air to vents.


If the air that switches to the windshield only is also hot, it would likely be that the AC is shutting off, but also dampers are moving. If the condenser high or low switches are turning of the air, I am pretty sure the compressor would stop, so if it doesn't stop when all this happens the AC is probably still running, although it will cycle off more of the time if the dampers switch to warm air.



I would not do anything with the switches until I confirmed the compressor going off when it happens. If it doesn't go off, then it is time to be checking the heater control and dampers.


The Dodges seem to have most of the trouble with the blend damper giving issues of heat all the time, or most of the time. There is currently one being looked at on a Roadtrek forum, also, and from what other Dodge owners mentioned there, it is pretty common.

[Kinch]

More great info thanks. I’ll have to get a bit more familiar with some of what you’re referring to and start tracking stuff down this week, will post any results..
Thank you

[JDBrown]

This is 100% a vacuum leak issue. The vent doors and the hot water through the heater hose are both vacuum controlled on these Dodge vans. I've been contending with it this week myself (I've got a 1999 Roadtrek 190 Versatile on the Dodge chassis). In my case, it switches from cold to hot and from dash vents to defroster vents when the van is under heavy load (long acceleration and/or long uphill), which is when the engine naturally pulls less vacuum.

The first thing to test is the check valve. You'll need to remove the doghouse and look for the bundle of little multicolored vacuum hoses under the dash on the driver's side. There's a one-way check valve on the black hose. You'll need to pull it off and try blowing through it. Air should pass through one way but be blocked the other way. Make sure you note which way it goes so you don't put it back on backwards. If the check valve is bad, replace it (they're cheap) and re-test. If it's good, put it back on and start looking for cracked vacuum hoses.

If you look under the hood, you'll see a little white vacuum hose coming through the firewall on the driver's side. It runs behind the isolator, and ends at a valve in the heater hose. On my RT, this hose was all full of little cracks--small enough that I didn't see them originally. Since I couldn't find a direct replacement for the original Dodge hose, I bought some 1/8" ID hose on Amazon, cut off the old hose near where it enters the firewall and near where it enters the heater hose valve, and then shoved the new hose onto the stubs of old hose.

The little testing I've been able to do since replacing that hose has been promising, and I haven't found any other vacuum leaks, but I decided to also install a 12V vacuum pump just in case. The idea is for the pump to assist when the engine isn't pulling enough vacuum to overcome whatever small leaks are in the system. I only went ahead and installed the 12V pump because I'm leaving on a multiple-months-long trip this week and I'm not 100% certain that I don't have any other undiscovered vacuum leaks. It was a bit more involved than I originally expected, because it turns out you need a vacuum switch as well (to turn the pump on and off), and I had to tap into a hot wire controlled by the ignition and install an inline fuse. But between the two fixes, I should have nice cold air throughout the trip.

[Kinch]

Fantastic, very promising.

I have the work grind for the next 4 days but will be working on it immediately after and will post results.

Thanks again ✊

[peppster66]

We have a 97 Dodge Roadtrek, and have had the exact same issue with ours, JDBrown was 100% correct about it being a vacuum isssue, all our vent doors run off of the vacuum pressure from our engines, the default is always the defrost way, find your vacuum leak and it will solve your problem.i went one step further and added a second vacuum ball just before the firewall and it fixed my problem, I’ll add a few pics to show what I did,,, good luck, it is fixable,,,

[Kinch]

Thanks peppster.
This is all new to me, checked around for a vaccume ball but will have to order it as my local auto guys are pretty basic.

[Kinch]

I feel like you all have me on the right track but the problem persists.
I pulled both check valves and they both appear to be fine (allow air flow one way and not the other).
I did notice a connector in the vacuum tube cluster that seemed loose but after reconnecting it tightly, same issue.

[Kinch]

I traced all lines and they seem to be without cracks. When I remove the check valve under the dash and put my finger over the tube going towards the engine end of the firewall I can feel suction.
One part I’m curious about is the one pictured.

[booster]

Originally Posted by Kinch

I feel like you all have me on the right track but the problem persists.
I pulled both check valves and they both appear to be fine (allow air flow one way and not the other).
I did notice a connector in the vacuum tube cluster that seemed loose but after reconnecting it tightly, same issue.

Buy yourself one of the cheap hand pump vacuum testers at most auto parts stores. You can pump up the vacuum by hand and see if it leaks down.

[Kinch]

Good idea. Will try tomorrow

[JDBrown]

Originally Posted by Kinch

I traced all lines and they seem to be without cracks. When I remove the check valve under the dash and put my finger over the tube going towards the engine end of the firewall I can feel suction.
One part I’m curious about is the one pictured.

The part in your photo is a vacuum-controlled heater hose valve. Suction in this hose closes the valve, blocking hot water and giving you cool air at the vents. Loss of suction in this hose allows the valve to open, allowing hot water to flow into the heater core and giving you hot air at the vents.

[Kinch]

Seems like it could be the culprit then if the rest of the lines and check valves are good which is looking more the case
Gonna try the vaccum tester tonight but will try to find that part either way just to get to the bottom of this

[booster]

Originally Posted by Kinch

Seems like it could be the culprit then if the rest of the lines and check valves are good which is looking more the case
Gonna try the vaccum tester tonight but will try to find that part either way just to get to the bottom of this

Hopefully, with the tester you will be able to remove the hoses one at a time at the control or use and adapter to test them through the mulithose connector if it has it that way. Then you can start to narrow things down a lot.

[jmai]

I had a similar situation with my 2001 Dodge Roadtrek. This is a well documented problem with the Dodge vans of that era.My problem was a loose hose at the ball shaped vacuum reservoir.

Many times the problem lies in the three knob heater control unit.

It looses a vacuum on the back of the unit. There is a vacuum line attached to the back of the unit. As you turn the heater distribution knob, it re-directs the vacuum to different ports and hoses, which in turn open doors to re-direct the heat (floor, dash, defrost etc). I read one post where the guy took the unit apart, lubed the vacuum ports and re-assembled it. Definitely a last ditch effort. Unfortunately, the part is fairly expensive so I would first check all the lines, check valve, vacuum reservoir, heater control and (I think) a cruise control unit. Try to find a diagram of the vacuum lines for your chassis and go from there.

If they all check out then consider the heater control unit on the dash.

[jmai]

Originally Posted by Kinch

Dash AC 98 Roadtrek cycles to hot air after driving for a bit

Hi all, I’m having an issue where the AC is working fine (refrigerant is topped off) and the clutch is engaging, cold air is blowing but when I’ve been driving for 5 minutes or so, the dash air switches to only windshield vents and starts to blow hot air.

I’m leaning towards one of the high/low or condenser sensors but I wanted to put the question out there before I start replacing things

Thanks in advance

Just re-read your post. The vacuum problem with the AC usually manifests itself when the engine is under a heavy load like passing, full throttle or going up a hill. Once the heavy load is off the engine, the AC air distribution usually returns to normal if the vacuum is fine.

You stated that after 5 minutes, you have no AC. Does it ever return? Where is the air distribution after 5 minutes? Try lifting your foot off the throttle and see if things change.

[Kinch]

Once the air switches to dash heat it stays like that until I’ve had the engine off for a while.

I’ll stack that on the list of things to check once I’ve check with vacuum tester, etc

[Kinch]

So I picked up a basic vaccum tester, when I test the line cluster shown in the pic, the black line going to the check valve then to firewall gets 10psi pressure. None of the others register but I'm presuming that they are to route the vaccum once different slots on the knob are selected?

I replaced the heater valve, by the way but that didn't fix the issue.

The other pic (sorry about the poor visibility), is that the vaccum reservoir?
Don't know how I'll get to that if so, looks like I may have to remove the headlight.

**I'll be removing the distribution knob next and will try lubing connections