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GMC truck A/C not cooling in town



 
 
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  #1  
Old July 21st 05, 04:52 PM
canmoe
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Default GMC truck A/C not cooling in town

I have a 96 GMC seira with a 350 vortec,the A/C cools fine at morning
startup or on the hwy,but when I go slow or am in town stop and go the A/C
stops blowing cooled air,I have charged it and its not low,I know the air
is flowing under the hood,I have cleaned it,can someone PLEASE help.
it is hot outside,Thank You!

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  #2  
Old July 21st 05, 05:55 PM
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canmoe wrote:
> I have a 96 GMC seira with a 350 vortec,the A/C cools fine at morning
> startup or on the hwy,but when I go slow or am in town stop and go the A/C
> stops blowing cooled air,I have charged it and its not low,I know the air
> is flowing under the hood,I have cleaned it,can someone PLEASE help.
> it is hot outside,Thank You!


In my experiance the A/c looses efficiency whenever the airflow through
the radiator (for lack of the right word) is reduced as in city
driving.

In my vehicle the radiator fan switches on to boost airflow.

  #3  
Old July 21st 05, 05:59 PM
Steve B.
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On Thu, 21 Jul 2005 11:52:11 -0400, "canmoe" >
wrote:

>I have a 96 GMC seira with a 350 vortec,the A/C cools fine at morning
>startup or on the hwy,but when I go slow or am in town stop and go the A/C
>stops blowing cooled air,I have charged it and its not low,I know the air
>is flowing under the hood,I have cleaned it,can someone PLEASE help.
>it is hot outside,Thank You!



Does your truck have electric or mecahnical fans? If electric make
sure they both are working and if mechanical make sure the fan clutch
is in good shape.

Also if you can check the high and low side pressures while it is in
"not cooling good" mode we can offer a little better advice.

Steve B.
  #4  
Old July 22nd 05, 06:31 PM
Ad absurdum per aspera
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Here are a few checks you can perform without getting out your gauge
set.* My experience has been that a/c is something GM did well in this
class of vehicle, and when functioning properly it should make things
good and cold.


1. Under circumstances when you think it should be cooling but isn't,
is the compressor clutch engaged? If you can't tell from behind the
wheel, find a parking spot where you can safely leave the engine
running and pop the hood and take a look. Some cars (dunno about this
one) have demand cutoffs that temporarily disengage the a/c compressor
when you accelerate, which you do a lot more often around town.

2. Does it give more satisfactory results on the MAX a/c setting? MAX
closes the air-circulation intakes, so you are recirculating the cabin
air and making it cooler and cooler rather than admitting hot outside
air.

3. What does your engine temperature gauge look like when this is
going on -- nominal, or getting pretty hot?

4. Is the temperature changer knob or slider all the way over to
"Cool"... and is the heater core aware of that fact? Unless they
changed it (along with several other things) between my '95 and your
'96, make sure the cable linkage between the two hasn't gotten slack
enough to be giving you heat...


Best of luck,
--Joe

* Though presumably you have a gauge set if you've been recharging
your own a/c... most cars have an overpressure cutoff switch in the
circuit, which presumably could be tripping under some circumstances if
you put too much in.

One of the widely available consumer-grade brands of gauge,
Interdynamics if memory serves, comes with a handy guide for
interpreting the high-and low-side reading and needle behavior and
other easily observed data.

  #5  
Old July 23rd 05, 10:18 PM
Comboverfish
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canmoe wrote:
> I have a 96 GMC seira with a 350 vortec,the A/C cools fine at morning
> startup or on the hwy,but when I go slow or am in town stop and go the A/C
> stops blowing cooled air,I have charged it and its not low,I know the air
> is flowing under the hood,I have cleaned it,can someone PLEASE help.
> it is hot outside,Thank You!


The airflow issues others mentioned are very likely. Make sure the fan
clutch gets stiffer as radiator temps increase. On a really hot day
sitting still it should practically lock up, causing that roaring sound
you are probably accustomed to. Other than that...

The blower speed switches are good for intermittant failure on your GM.
When your problem occurs, look at the A/C button and make sure the
light on it is lit. If the A/C button is depressed and the blower knob
is set to anything but "Off", then you probably have a bad blower
switch if the A/C indicator light is off.

It's actually more common for the blower switch to cause A/C compressor
engagement when in the "Off" position, but any problem is possible with
this GM switch.

Toyota MDT in MO

 




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