2004 Astro - a/c stops blowing on hard acceleration

[justice]

This just crept up on me, but I really noticed it on two long drives to Oklahoma. If I needed to accelerate harder than normal, like going up a long hill, My a/c would quit blowing through the a/c vents. It would come back after I let off the gas and let the RPM's come down.

Now, to add to the issue, when I start my van in the morning, the air is blowing out of the lower vent and the defrost vent. and after a little bit it will change and come out the front vents (where it is set and supposed to be coming out) My mechanic checked it out but could not duplicate the issue, but now it seems to be taking longer for the vents to switch after starting the van.

I know someone on here has dealt with this before, hook me up!

[Kidhauler]

The vents are vacuum controlled you might have a leak in the system. There is a vacuum ball that is supposed to hold vacuum to help keep suction to the vents in the case of prolonged or hard acceleration. However if your on the gas long enough that will run out. If it changes the vents every time you pull out to pass then you have a leak it could even be a crack in the ball.

Hope this helps good luck

[photo_van]

A common problem that is talked about on here somewhere? Under heater maybe?

There are some vacuum lines that go to a solenoid on the passenger side engine compartment (near the heater). I can't remember exactly what they do, but on two vans I've worked on with this symptom, those lines were completely disintegrated. Short lines, easy to replace and fixed the problem.

There is also a longer line (of hard plastic) that goes from that same area and travels over the top of the engine and attaches to a port on the drivers side. I have heard that that line can be symptomatic as well.

Hope that helps.

[LiftedAWDAstro]

Look through the diverter valve vacuum line thread. I bet this will resolve the problem.

[blacknome]

pretty common problem which comes up moreso in winter

As mentioned the vacuum lines tend to rot out. When you open the hood and look to the left , mounted to the heater box you will see the vacuum lines. The main vacuum line runs over and to the back of the motor ( when it rots the system loses all vacuum and you notice that you only have default defrost setting ). Under brisk acceleration an engine drops in vacuum ( hence the vacuum reserve ball ). Because the vent doors are vacuum controlled they will not operate with a leak in the system under acceleration but at idle the engine may produce enough vacuum to compensate for a small leak or cracked line.

Look at that main line, follow it back to the where its getting manifold vacuum, and then where it splits on the heater box, the heater control valve and the lines to the vacuum ball. If the line is soft and chalky then do yourself a favour and replace them all. Mine had cracked at the vacuum ball ( may need to remove the inner wheelwell on the PS to get to it ) and was showing the same symptoms.

[justice]

well, I looked under the hood today and saw a pretty badly cracked vaccum line at the heater bypass valve. So tomorrow I'm going to stop by the parts house, get a new valve and some vaccume line and hope replacing that small section will solve the issue. the line that goes over the engine looks ok except for the end, i'll probably trim the bad section off and reattach that line. The smaller hard plastic line looks ok.

[justice]

and success! Replaced the check valve (just because) and the really really bad piece of tubing from the check valve to the firewall. And I trimmed the ends off the the other lines. Now when I start the van the air comes out of the dash vents right away!

Strangely, only Advance Auto parts carried the A/C Delco check valves. Oreillys, only had Dorman, AutoZone and Napa didn't even list the parts (going by their websites)

I did get enough tubing to replace the other lines should they need it, but the other lines were in much better shape then the one I replaced.

[LiftedAWDAstro]

It's nice when it blows the air where you want it!