Weird Occurrence with vents

Hey all, I'm new, and I searched for a thread with the answer to my problem, but didn't find one... here is my issue:

When I have either the Normal A/c on or just vent selected,

1) is it normal for the air to come out of the top vents in the dash (near the windshield) when i accelerate? (usually this happens around 3000 rpm or after 65/70 mph)

2) If it isn't, then what could possibly be causing the problem?

Any help would be appreciated... i just got my 95 black lt 4 door 4wd blazer and i love it, but that bugs me!

No, not normal, you have a vacuum leak, trace the vacuum lines going to the vacuum ball in the engine bay.

Driver's side firewall corner.

You know what. I am going to start answering more questions. I think I have learned everything I need to know about Blazers now. I will tell people "check for a vaccum leak". :rofl:

Just joking, seriously though I got the same problem with mine. I never really cared much about it though because it always goes back to the vents a few seconds later. I may go check it out since I am goin to go stare at my Blazer some more in a bit.

RedLT,

You would be amazed as to how much vacuum controlls this engine.

No, not normal, you have a vacuum leak, trace the vacuum lines going to the vacuum ball in the engine bay.

Driver's side firewall corner.


Thanks for the information, I'll check that now, because it's been really bugging me. Nice car btw. looks like i want mine to look

RedLT,

You would be amazed as to how much vacuum controlls this engine.

Nothing amazes me except how Barney is still popular among kids. I know to well how much a vaccum leak can mess with a car though. I had that problem once before and I ended up selling the car because I couldn't figure out what was wrong with it. I don't know much about cars really. I can fix most minor problems like changing a starter or something but when it comes to knowing what an EGR is I am stumped.

Your truck's a '95 with the CPI, RedLT? Easy to find it. Take a peek between the tensioner's idler wheel, the underside of where your air intake leads to the plenum, and just above the pulley of your water pump. See that black, round, plastic thing with the 4 wires in a connecter sticking out straight back at you? That's your EGR. I have had mine off several times to clean it as the truck went through a phase of "couging up a lunger" - twice it got stuck completely open or shut, each time it was because of a chunk of carbon in it. She's quieted down after having to come off three times total. I am waiting for it to stay clear for a while and then I will give it a fresh gasket I have sitting in the back of the truck. I was lucky and able to salvage the new gasket put on it after the first time it came off two more times, but it's good to be sure and have it put back on every time with a fresh gasket. My reluctance is only because of the wait time involved in getting the right one shipped in, they're cheap - but nobody *stocks* them. Not here anyway. :)

Thanks for the information, I'll check that now, because it's been really bugging me. Nice car btw. looks like i want mine to look

Good luck and thanks.

okay, well i changed the vacuum lines, which were very badly deteriorated, but the problem still happens... my mechanic (who was nice and didn't charge me to do an inspection) said it might be one of the vacuum valves, and will check for free. he said the fix might cost about $40.

Although this might be another problem... sometimes there is a buzzing noise coming from the windshield defroster vents... it happens occasionally, and isn't electronic or anything... is this the same problem or different, y'think?

Did you check the connection going to the vacuum ball?

Did you check the connection going to the vacuum ball?

yeah, that was the first thing that I changed... the rubber was disintegrating on the hose, so i just replaced the whole hose set... i mean, at 9 cents an inch, how can you go wrong? cost me less than $5, so it doesn't bother me that it didn't fix it, but i would like to fix it. Vacuum ball connection is secure and tight though, with the new hose.

sometimes there is a buzzing noise coming from the windshield defroster vents... it happens occasionally, and isn't electronic or anything... is this the same problem or different, y'think?

I get that same buzzing noise when it switches from my vents to my defroster. If issues this small bug you then I want to buy your Blazer when you get tired of it. Someone who breaks there back to fix a problem so small must really take care of there truck. I treat mine like a baby but I don't usually sweat the small stuff like that.

how much would a vac leak affect the gas mileage? i know it would effect the idle. right now mine at idle sounds like it has a cam in it. i don't know if its from the cat taking a dump or vac leak. i do have the same prob with the vents though. everything looks good also.

Does it rev up and down constantly?

nope. just idles like theres a cam in it.

Where's the vacuum ball located on a 98 Blazer Vortec?

Would air blowing through the vents while moving (with all controls off) be a vaccum issue?

I get that same buzzing noise when it switches from my vents to my defroster. If issues this small bug you then I want to buy your Blazer when you get tired of it. Someone who breaks there back to fix a problem so small must really take care of there truck. I treat mine like a baby but I don't usually sweat the small stuff like that.

hahaha, it's not a must-fix, and it doesn't bug me like the vents switching does, but i really do baby mine. About the buzzing noise, though, it's not when i switch from anything, and i was just curious about it.

Where's the vacuum ball located on a 98 Blazer Vortec?

Would air blowing through the vents while moving (with all controls off) be a vaccum issue?

Look in the engine bay in the driver's side back corner.

Would it be under anything; like the ABS?
I peered around over there (with a flashlight; at night... might help to look in the daylight) and couldnt see much.

Would air constantly blowing through the vents (only when moving) be a vacuum related issue? Or another door-related issue like the fresh air/recycle door?

I think these problems are related to the sounds I was hearing when these things started happening. Two sounds I heard from under the dash at any random time were (dont here them now):
1.) A metallic "ka-pling"
2.) A low purring type noise that lasted for about 3 seconds; probably vacuum related.
I dont here these sounds anymore. I only heard them when this stuff started happening.

The ka-ping is a normal noise and is the dash flexing when the temperature changes.

The air coming out the vents when it is turned off is a sign that you have a vacuum leak in the HVAC system that is not allowing the controls to turn the ventilation system off.

What part would allow air flow to come in if the control cant close it?

There isn't enough vacuum for the controls to close the airflow door.

how much would a vac leak affect the gas mileage? i know it would effect the idle. right now mine at idle sounds like it has a cam in it. i don't know if its from the cat taking a dump or vac leak. i do have the same prob with the vents though. everything looks good also.

last week my vac line broke off the upper intake and i lost 2mpg on that tank of gas. vac has a great affect on the cpi 4.3

darn right it does.

You know what else hurts economy, huge 18 inch wheels and 255 width tires.

darn right it does.

You know what else hurts economy, huge 18 inch wheels and 255 width tires.

Amen.

A vacuum leak could effect 2 or 3 mpg if bad enough to effect the idle like that and it can make the engine run lean too which will make it run hot . The buzzing sound, could it be a leaf in the blower? When you open the throttle to accelerate , the vacuum strength decreases which causes your vents to change . Mine does not have a vac ball anymore(but I want one) and my vents are constantly changing as I drive . I have a leak on my valve inside the dash and I need a new one . But am not bothered by it enough to tear the dash apart to get it out far enough to do the job . Mine does not effect the engine since I converted to a carb .Rob