[Shop-talk] trucks a/c

[David Scheidt]

On Thu, May 27, 2010 at 11:45 AM, Randall <tr3driver at ca.rr.com> wrote:
>> As far as I know, the system was evacuated and refilled. I will verify
>> this. If it needs to be evacuated and refilled, what are the chances of
>> this working? Is the R134a that poor of a refrigerant that I will end
>> up SOL?
>
> As David said, since it was a R134a system originally, it should be
possible
> to get back to the original performance.
>
> Unfortunately, with so much already done, I don't think anyone is going to
be
> able to troubleshoot it by remote control. B You need to find a competent
shop
> and have them run tests to determine what the problem actually is.
>
> One area that has given me trouble in the past with GM AC is the expansion
> orifice. B Apparently some of the aftermarket parts don't flow the same as
the
> original, which causes less cooling. B Or else mine was getting clogged
from
> debris left in the system after the compressor was replaced; not sure.
B But
> that was an R12 system, I don't know offhand if the R134a systems even use
an
> orifice or not.
>

As far as I know, all GM AC systems have some sort of orifice tube.
(since they invented them, in the mid 70s, at least.)  Not many cars
still use valves.  In many cases, it's possible to put a tube with a
bigger orifice in,  and increase the cooling capacity of the system.
This is something that does get screwed up.  Most shops that do AC
work have a kit of tubes and other small parts (filters and orings),
which saves having to order them for every car that comes in.   but
kits get messed up, and the parts put in the wrong tray (or the shop
runs out of something, and the tech is too lazy to reorder!), so the
wrong tube can get installed.

My diagnostic path for a vehicle with this complaint and history would
be about this:

visually verify that the vehicle has the right compressor, condenser
and evaporator.
Verify that operating pressures are correct, and that it shuts on and
off at the right points.
evacuate and charge with proper mass of r134a
still doesn't work, then evacuate and replace filter and orifice tube.
 recharge.
Scratch head.

I don't know what the shop has done.

--
David Scheidt
dmscheidt at gmail.com