Vacuum line

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rbunkley

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Joined
Mar 6, 2017
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Location
Trenton, SC
We have a 2005 Four Winds Chateau Class C. The vacuum line that controls our AC vents is leaking. When the engine is under a load the air diverts to the defroster instead of coming out the front vents. It's now getting worse. Had an estimate of $800 for just labor to fix it. Any other options?
 
Well, you could pull the radio, the HVAC controls, and glove box and have a look. Its possible a hose has simply come loose. If they are really rotten you should be able reach most of them with the daah opened up.
 
It doesn't sound unreasonable to figure it'd be a day to tear into that and trace it down, and shop rates of $100/hr are not unusual. If you're willing to do a little poking around odds are good you'll find the busted fitting or shot vacuum actuator causing the leak.

Mark B.
Albuquerque, NM
 
When the engine is under a load the air diverts to the defroster instead of coming out the front vents.
Click to expand...

That doesn't sound like a vacuum line to the AC leaking that sounds like a vacuum leak in the engine.

A vacuum line to the AC would leak all the time, not just when the engine is under load.

Why would a hose leak more when the engine is under load?

I think you may have engine problems in your future. I hope I'm wrong.
 
rbunkley said:
. The vacuum line that controls our AC vents is leaking. When the engine is under a load the air diverts to the defroster instead of coming out the front vents. It's no
Click to expand...
I don't know about your rig, but I have had that problem caused by a small ten dollar vacuum valve in my Jeep.

I would start by trying to find such a valve and also your vacuum reservoir. I agree with JayArr your problem is most likely near the engine where it can be repaired (in most cases). The hose most likely was destroyed or melted by engine heat. It's rare to have hose damage up by the vents.

But JayArr-- there is LESS vacuum under load because you're on the accelerator. Most vacuum is right at idle when the air intake is most restricted. As soon as you put pressure on the accelerator, vacuum is decreased. The least vacuum is at WOT, such as racing uphill. That is normal. So they install a vacuum reservoir to hold vacuum when going fast uphill and such because if there wasn't then there would not be enough vacuum to run the vents so they relax to the defroster position. The good news is the A/.C still works, just blows too high to feel as strongly when there is a leak in vacuum.

Problem can also be caused by a crack in the vacuum reservoir or a poor connection at the hose to it.

-Don- Reno, NV
 
DonTom said:
But JayArr-- there is LESS vacuum under load because you're on the accelerator. Most vacuum is right at idle when the air intake is most restricted. As soon as you put pressure on the accelerator, vacuum is decreased. The least vacuum is at WOT, such as racing uphill. That is normal.
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True -- we used to see this visually when the windshield wipers were run from engine vacuum. They'd slow a lot when you stepped on the gas.
 
My first thought was, "vacuum line fell off the reservoir".
When I first test drove the Jeep I now have, the heater wouldn't switch off of defrost. I opened the hood and found the line to the heater controls disconnected from the vacuum reservoir.
Fixed it before I could stop myself and then couldn't use "heater inop" as a bargaining point to lower the price.
 
How would a vacuum leak in a line get worse when the vacuum is decreased.

If you take a hose and apply 10 inches of vacuum to it and then prick a hole in the hose with a pin it will leak. Let's let this be indicative of full vacuum at idle.

If you then reduce the pressure to 5 inches of vac (to simulate WOT) it will still leak and it won't leak more, it will leak less, because the vac pressure is less.

I don't think this will be a leaky hose, leaky hoses don't act like he describes.

I hope it's something simple.
 
JayArr said:
How would a vacuum leak in a line get worse when the vacuum is decreased.
Click to expand...
Nobody is saying the leak gets worse. The vacuum gets weaker and weaker when the accelerator pedal is pressed down more, even if the hose is perfect.

Less vacuum from a small tear in a hose can cause no problems at all at idle when there is a lot of vacuum available. But there is very little vacuum available when the "pedal is to the metal" and then that same leak can cause problems. Then every drop of vacuum is needed to keep the flap down for the A/C mode, but then there isn't enough vacuum to do the job with that small vacuum leak from the hose is added in.

IOW, the hose vacuum leak gets much more critical as the accelerator pedal is pressed down. So the problem is often only noticed when going uphill.

-Don- Reno, NV
 
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"When the engine is under a load the air diverts to the defroster instead of coming out the front vents."
That is the default setting if you loose vacuum.
Bill
 
Most likely there is only one vacuum line that runs from the engine compartment thru the firewall. If there is more than one clamp one at a time until you identify the one that controls the A/C.

Mine had plastic lines but had a rubber connector that cracked and caused this problem. But if you find the leaky vacuum line and can't get to it, just get a "T" connector and splice the A/C into another good vacuum line and plug the original line.
 
JayArr said:
That doesn't sound like a vacuum line to the AC leaking that sounds like a vacuum leak in the engine.

A vacuum line to the AC would leak all the time, not just when the engine is under load.

Why would a hose leak more when the engine is under load?

I think you may have engine problems in your future. I hope I'm wrong.
Click to expand...
Engine vacuum volume is reduced the farther the throttle is opened ( ie under a load )
I have the same problem with a Jeep Wrangler
 
Fastlane Tracks said:
Engine vacuum volume is reduced the farther the throttle is opened ( ie under a load )
I have the same problem with a Jeep Wrangler
Click to expand...
Check that $6.00 valve I mentioned in message 5 above and make sure it is not in backwards. It fits in perfectly backwards on some Jeeps and that will guarantee your A/C air will blow out the defroster vent with the slightest hill.

I had the problem on a 1997 Jeep Grand Cherokee (5.2L) that I recently junked.

-Don- Reno, NV
 
I'm with Don; the lower the vacuum, the more likely the valve will drop out.
In any event, the way to locate the leak is probably to spray, lightly, any suspect areas of the vacuum system with starting fluid while watching for spikes in engine rpm. If the leak is close to the manifold, the change will be noticeable.

Ernie
 
You didn't say what brand chassis you have. I have e a 2006 Ford chassis and most of the time, the problem is a broken vaccuum reservoir, which is in an inaccessible location. That's why they want so much money to fix your problem. Go to you tube, and there a numerous videos for relocating another vaccuum tank under the dash, to fix your problem. Check the one way vaccuum valve under hood first, though. If you are handy with tools, you tube is your friend.
 
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