So I had a New issue arise yesterday on my way to the Flying Field which
is about 40 miles away... as I was speeding up to get onto the express
way.. the AC ( Air coming out of the Vent ) dropped... almost like went away.
now I know that the vent controls are controlled with vacuum.. but the air
coming out of the vent if like my truck.... is controlled by electric rheostat
why would the vent pressure which is electric dissipate during excelleration ?

 

Did it came back when you achieved speed? And when it faded, did it go to defrost? If so, it is definitely vacuum related. Astro's suffer from a lack of vacuum. This fade happened every time I floored it, and going up most long hills on the highway, in my '00 Astro. It is a design flaw in Astro's that can't be fixed. I sure as hell don't miss that. But it shows a possible leak in this situation. Not easy to track down.

 

as far as it going to defrost.. I wouldnt know that.. the speed of the fan went away...
as if the fan motor was disconnected.. then reconnected... its strange .....
if the fan motor just went to defrost.. you would hear that change.. but it didnt do that
it just stopped working... so im curious to know if vacuum some how controls the motor speed too ?
I dont know its weird...

 

I know there has been some vacuum issues in the past because there are repairs
that you can see under the dash on the passenger side....
I think its at a junction box... were all the lines connect.

 

Usually, fan speed is a function of a resistor block, which should be energized by the same controls the switch the vacuum. I seriously doubt they'd make a separate vacuum switch to energize the fan.

But if the fan is truly cutting off, I'd look at the resistor block. My Astro had a fan issue, where the plug that connected to the resistor melted, scorched, and corroded. It seemed that the high speed setting caused the high current to overheat it. The resistor block is mounted so it is "cooled" by the intake of air into the HVAC ducting, under the hood.

Because of this issue, I rarely use high speed on the fan.

 

Blower motors can go bad too. I had one that occasionally needed a whack with a hammer to get started. (Bushing seized)

When a blower motor stalls, it will stress the resistors which Stan mentioned and eventually burn em out. They are very easy to access. Right under the windshield on the passanger side. Just two screws to loosen and out they come. Check for scorching.

You might want to mention what you drive.

 

mountainmanjoe REALLY... ( LOOK ) at my Avitar Picture.

 

I saw the thumbnail of a red extended van.

If you want to make it easier for people to help you, they need the year, model, and engine. Pretty standard procedure no?

 

I agree with that statement ... ( too A degree ).....
example....
Engine CODE.. is not going to make a difference in this case...
Extended or Short version is not going to make a difference either...
The Year... depatable... too seeing that I have posted many times in
this forum and the van has been around for 17yrs.. ( lmao )
Model.. not going to make a hill of beans when talking about a
Express..Van... with an erratic blower motor when excellerating
so I really dont think that statement applies here.

I have a GMC Sierra...... Pickup.... and I wouldnt be posting about a problem with that here in the Van forum..
I could easily go over there were I have a thread as well....
MY THOUGHTS..... I would have posted an entirely new thread so MORE PEOPLE would be able to see it
rather than just posting on the same thread I have started.... so I guess in your case.. I should have posted on
my original thread so you would have known that I was talking about my van.
regardless... its all based on someone else thinks.and you know what I say about that...
you cant please everyone all the time.. I really didnt think I needed an introduction while talking about an issue
I was having... Since having my VAN... and been junk yarding for said VAN.... I have noticed that regardless
of MAKE MODEL and YEAR... they really didnt change that much.. and honestly I think that is SAD.. for a manufacturer.
IMOP.... But I will say this.... in the area that I live in and you might have to read my profile... for that one....
I sure see ALOT... of Chevy or GMC vans...
Gear change.
I am very aware of the resistor in the heater or AC box... but I just cant understand how it would do the symptoms I had
described... electrical.. either its working or its not.. but while under heavy excelleration how in the world.. does it drop the
speed of the blower motor ?
that too me sounds electrical but vacuum operated somehow.. just strange ... so if you know how its wired and operates
with out a dought or if someone has run across this issue ... cause its strange...it sure would save me alot of time in
diagnoising. the problem...

 

Think of it this way Ron. If it is indeed scorched and melted, the inertia from acceleration might pull the connector from making contact. stopping the electricity momentarily. My Astro did this when the plug was going bad. I've not seen the resistor itself go bad too often, unless the fan motor goes bad. In my case, the motor wasn't totally gone, it just drew too much current on high, and melted the plug. But it spun until I traded it.