Is this normal?

When I have the a/c or just air blowing at the 3rd or 4th highest setting, and I put it onto 5th gear at 40mph and gas it hard, the air stops blowing after about 3-5 seconds. After I let off the gas, the air starts blowing full force again.

What's going on? Is this normal? I know the a/c compressor clutch disengages at WOT (i think), but air should still blow... any reason why my air stops blowing?

 

You have a vacuum leak. There are four doors inside the HVAC duct work that deflect the air to the appropriate vents when selected. The default position is feet and defrost. That is, when there is no vacuum (as in limp home) the vents will default to feet/defrost. Any other position selected has to be held open with vacuum. In your case (as I had too), when you stomp on it, vacuum level goes down, and the door that was being held open closes. The default door, feet/defrost, takes over. It seems too you that the blower is slowing down (as did me) but in actuallity, the blower is staying the same speed and the vents are switching to the feet and defrost position.

So what do you do to fix it? Every person probably has their own way to do it but I'm from the simple (lazy) school and quick too since we charge by the hour. I like to split the vacuum system into 2 sections. 1 in the engine compartment and the other in the cabin. Start by pulling off one of the hoses,(I think it's the bottom hose) on the check valve at the fire wall near the PCM. If you get a quick release of pressure and hear the air rushing in, chances are good the system in the engine bay is ok.

What you did was let air back into the vacuum resevoir located behind the front bumper. If there were a leak upfront somewhere you would not have heard the rush of air back in when you pulled the hose off. In that case, you will have to locate the source of the leak somewhere between the check valve and the canister.

If air does rush in when you pull the hose off, the problem is in the cabin. What I feel is the easiest thing to do is remove the hose cluster from the HVAC control **** assy and test each individual hose going to each door (called actuators).

At the control is 5 hoses, a black one provides vacuum from the engine and 4 colored ones for each actuator. Check the black one for a vacuum level near 20 PSI. I used a mityvac brake bleeder. If you rev up the engine while monitoring the black hose and the level drops off, you know the problem is back toward the engine bay. If it is ok, put the vac on each colored hose and draw a vacuum and see if it holds. The one that does not hold is the problem. I forgot the color coding but someone will give it to you if you need it.

BTW 3 of those 4 doors are a M!@#ER F!@#ER to get to. I was so lucky that my problem was the bi-level actuator hose fell off. It is the only easy one to get to.

Sorry long
Good luck
Dave

 

Dave -

Thank you, so much! For that long detailed post, it was incredibly helpful in troubleshooting my vacuum system.

You see, I've had this unexplicable powerloss, hissing, hesitation under load. I was suspecting a vacuum leak, so I redid the intake manifold, the pcv system, and all the topend hoses, but nothing helped. My brakes were loose as well.

So, following your advice, I pull off the black hose from the bottom of the check valve. I don't have a vacuum pump, so I just use my mouth to suck on it (rowr), and put my tongue over it to see if it holds vacuum, or leaks. Well, it just felt like I was sucking on an empty straw, and I heard a hissing coming from under the battery.

So, I pull off the lower pass. side splash cover from the bottom, and look at the vacuum canister. It looks fine, but.. crap! I yank on the black hose and it comes right off in my hand. It was corroded, split, and broken into two pieces from some older leaking battery acid.

I cut off the corroded parts of the hose and connected them with some teflon tape and a rubber grommet, for now.

The car runs f*cking GREAT! The car still slightly "hisses" under load, but its much less noticeable. The brakes are *MUCH* firmer, and the car feels like it has twice the torque from idle to 6k rpms.

Thank you so much Dave, you probably don't understand how glad I am to have this year-long hesitation/hissing problem off of my shoulders. I was about ready to sell the car!

If you're ever in the LA area (or Berkeley/SF area before 7/3/04), give me a buzz (or PM me) - I'd like to buy you a couple beers, or dinners, what not.

Thanks again, Dave.

- Kyung

 

Thanks Dave, I have the same problem.

 

Very common for that hose to suffer damage by the battery. It also can get cut on the metal edge as it loops down. After I replaced mine, I put some tubing around it to protect it.

You can also use the appropriate size vacuum hose to join two pieces of the hard plastic hose.

 

I would love to come to LA but alas I have a business and can't spend the time but T'm glad you got the problem fixed. Now you can help someone else with the same problem.