Is it normal for hot or cold air to stop coming out of the vents when the engine is under load? When going up a hill air stops coming out if the vents and starts again when no longer working hard. 99 tj 4.0
Is it normal for hot or cold air to stop coming out of the vents when the engine is under load?
- Thread starter Crashmymax
- Start date
No, not normal. The blend doors of our HVAC system are vacuum operated, you most likely have a vacuum leak somewhere, maybe in one of the actuators. When the engine is under load vacuum drops in the intake manifold & the air switches momentarily to the defrost position instead of the dash vents. Have you noticed it doing that specifically?
OP
Ok maybe it is working correctly. I need to check and see if it is coming out the defrost vents. Probably a good time to go through all the vacuum lines anyway.
X2 on being a vaccum leak. Mine was doing it pretty bad, the more gas you give it, the more air goes to the defrost instead of selected vent. I found a split vaccum hose under the battery tray. I fixed that and my problem was gone.
OP
Start with the line coming off the intake manifold. Many rubber connectors there that deteriorate due to heat. You can buy the entire line as a replacement for cheap enough.
Edit - link was not working. Try searching for this:
Part no: 55037567AC
Edit - link was not working. Try searching for this:
Part no: 55037567AC
MOPAR VACUUM HOSE AND VALVE
I've been experiencing what sounds like the flapper door opening and closing as I press the gas pedal and let off, is that system behind the dash and against the firewall, and will the battery need to be removed to check out the vacuum line underneath?
That's a vacuum problem, not a flapper motor issue. There's an entire vacuum line system that needs to be looked at for leaks, not just the possibility the vacuum reservoir might be missing (or leaking).
Start the engine and spray all the various vacuum lines and fittings with something like a throttle body or carburetor cleaner. If the spray finds a leak the engine will suck the cleaner inside and cause the engine to stumble. Item #8 below is the reservoir I mentioned.
OP
Sounds like a vacuum leak. Check out that diagram Jerry posted up above, it’s not uncommon to find split lines in the engine bay.
TJScott
TJ Enthusiast
I have an 03 that does the exact same thing. I replaced the vacuum line in the engine bay. But it didn’t help. I figured it couldn’t hurt even if it wasn’t the issue. Obviously, I have more chasing down to do. I will use the diagram and check some of those areas.
I chased down a leak last year, found a split right near figure #2 in the diagram above. While I was at it I just replaced all of them with about 4 feet of bulk vacuum line from NAPA.