99 Grandprix automatic climate control (Airconditioner) issues, failing AC after periods of time..

I have a 99 GT grandprix with the computer controlled/set climate
control system.

After about 1 hour on the road the AC fails to output air from the
vents.. if you turn it down to say 60, you can hear the motor running
hard, but no air comes out... The same thing occurs if you
immediately switch to "heat".

If you unpress Auto and leave it on manual, air comes out just fine as
far as I can tell.. with no loss of output over time.

It would be nice for the automatic setting to actually work...

Anyone run into this and know of a possible solution?

Cheers

We just went through a similar situation with a 98 Buick, although possibly
not exactly the same.

The Buick started intermittently failing to put cold air out through the
vents,
but the blower motor was running strong. Finally intermittent became
permanent.

The vacuum module which controls the diverters was not able to overcome
the resistance of the mechanical diverters. They were lubricated and freed
up,
and now the system works pretty much as factory.

IF the freeup job hadnt held, we would have had to replace the vacuum
module,
and that costs several hundred dollars. This is not an uncommon problem
with
GM. The POS HVAC computer is another rather common failure.


"markm75" > wrote in message
ps.com...
> I have a 99 GT grandprix with the computer controlled/set climate
> control system.
>
> After about 1 hour on the road the AC fails to output air from the
> vents.. if you turn it down to say 60, you can hear the motor running
> hard, but no air comes out... The same thing occurs if you
> immediately switch to "heat".
>
> If you unpress Auto and leave it on manual, air comes out just fine as
> far as I can tell.. with no loss of output over time.
>
> It would be nice for the automatic setting to actually work...
>
> Anyone run into this and know of a possible solution?
>
> Cheers
>

On Jun 11, 11:38 am, > wrote:
> We just went through a similar situation with a 98 Buick, although possibly
> not exactly the same.
>
> The Buick started intermittently failing to put cold air out through the
> vents,
> but the blower motor was running strong. Finally intermittent became
> permanent.
>
> The vacuum module which controls the diverters was not able to overcome
> the resistance of the mechanical diverters. They were lubricated and freed
> up,
> and now the system works pretty much as factory.
>
> IF the freeup job hadnt held, we would have had to replace the vacuum
> module,
> and that costs several hundred dollars. This is not an uncommon problem
> with
> GM. The POS HVAC computer is another rather common failure.
>
> "markm75" > wrote in message
>
> ps.com...
>
>
>
> > I have a 99 GT grandprix with the computer controlled/set climate
> > control system.
>
> > After about 1 hour on the road the AC fails to output air from the
> > vents.. if you turn it down to say 60, you can hear the motor running
> > hard, but no air comes out... The same thing occurs if you
> > immediately switch to "heat".
>
> > If you unpress Auto and leave it on manual, air comes out just fine as
> > far as I can tell.. with no loss of output over time.
>
> > It would be nice for the automatic setting to actually work...
>
> > Anyone run into this and know of a possible solution?
>
> > Cheers- Hide quoted text -
>
> - Show quoted text -

Interesting tidbit.. thanks...

But in my case, as it works fine on manual.. would this still indicate
an Vacuum issue.. I would think it may be more along the lines of the
"headunit" or computer itself, which I think I can find a used
replacement fairly cheaply?

Cheers

> Interesting tidbit.. thanks...
>
> But in my case, as it works fine on manual.. would this still indicate
> an Vacuum issue.. I would think it may be more along the lines of the
> "headunit" or computer itself, which I think I can find a used
> replacement fairly cheaply?
>
> Cheers

We had the computer replaced a couple of years ago. Ran about $600 new.

Always possibilities at junkyards, if you are careful. If you go to the
wrecking
yard and find a car with a good (?) vacuum module in it, you might want to
pick it up. They are not encased, so do not tolerate rain, exposure, well.

Good luck...Too damn hot here to be without a proper AC.

On Jun 11, 2:49 pm, > wrote:
> > Interesting tidbit.. thanks...
>
> > But in my case, as it works fine on manual.. would this still indicate
> > an Vacuum issue.. I would think it may be more along the lines of the
> > "headunit" or computer itself, which I think I can find a used
> > replacement fairly cheaply?
>
> > Cheers
>
> We had the computer replaced a couple of years ago. Ran about $600 new.
>
> Always possibilities at junkyards, if you are careful. If you go to the
> wrecking
> yard and find a car with a good (?) vacuum module in it, you might want to
> pick it up. They are not encased, so do not tolerate rain, exposure, well.
>
> Good luck...Too damn hot here to be without a proper AC.

Thanks...

I did see the climate control computer on ebay used once for around
$100, however now I can only find this one:

http://cgi.ebay.com/ebaymotors/97-Gr...30093392QQrdZ1

Roughly $300. This states 1997 GrandPrix, but i think from 97 till
2003? the AC controller unit is the same as in my 99?

On Mon, 11 Jun 2007 07:36:41 -0700, markm75 > wrote:

>I have a 99 GT grandprix with the computer controlled/set climate
>control system.
>
>After about 1 hour on the road the AC fails to output air from the
>vents.. if you turn it down to say 60, you can hear the motor running
>hard, but no air comes out... The same thing occurs if you
>immediately switch to "heat".
>
>If you unpress Auto and leave it on manual, air comes out just fine as
>far as I can tell.. with no loss of output over time.
>
>It would be nice for the automatic setting to actually work...
>
>Anyone run into this and know of a possible solution?
>
>Cheers

How long doe it take for the air to start coming back out again? I
have seen several cars where the low pressure switch failed on the
a/c. After a while on the hwy the evap would freeze over and you
loose air flow. Turn off the compressor for a few minutes and it
would thaw out and then you could start the cycle again. Low pressure
switch is very cheap and you don't have to drain the system to replace
it on most cars (make sure your car is one of those "most" before
unscrewing the switch).

Steve B.

On Jun 11, 7:00 pm, Steve B. > wrote:
> On Mon, 11 Jun 2007 07:36:41 -0700, markm75 > wrote:
> >I have a 99 GT grandprix with the computer controlled/set climate
> >control system.
>
> >After about 1 hour on the road the AC fails to output air from the
> >vents.. if you turn it down to say 60, you can hear the motor running
> >hard, but no air comes out... The same thing occurs if you
> >immediately switch to "heat".
>
> >If you unpress Auto and leave it on manual, air comes out just fine as
> >far as I can tell.. with no loss of output over time.
>
> >It would be nice for the automatic setting to actually work...
>
> >Anyone run into this and know of a possible solution?
>
> >Cheers
>
> How long doe it take for the air to start coming back out again? I
> have seen several cars where the low pressure switch failed on the
> a/c. After a while on the hwy the evap would freeze over and you
> loose air flow. Turn off the compressor for a few minutes and it
> would thaw out and then you could start the cycle again. Low pressure
> switch is very cheap and you don't have to drain the system to replace
> it on most cars (make sure your car is one of those "most" before
> unscrewing the switch).
>
> Steve B.- Hide quoted text -
>
> - Show quoted text -

Thanks for the tip..

It seems to be about 3-5 minutes for it to come back out full force
again, however, I can switch to "manual" mode and have somewhat decent
a/c flowing this way, even after it stops coming out, would that still
indicate a low pressure switch?