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Old 12-07-2005, 02:01   #1 (permalink)
Baz
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Air Cond - 96 850

Hi,

I have reason to believe the air conditioner low pressure "pressostat"
switch is intermittently faulty in my 96 Volvo 850. It is a non-climate
control system. It has the correct charge (750g) and a gauge on the low
pressure side seems to point to the switch being bad. The symptom is that
sometimes the a/c will cool properly, 3deg C from the vents, with outside 33
deg, and other times the compressor will only stay on for perhaps one
second, and of course not cool at all. One instance of this, with the
pressostat plug s/c, the compressor would start and with ambient over 40deg
C, 15 deg C from the vents, and the suction line to the compressor is
sweating but not freezing. With the pressostat in circuit, compressor short
cycling. Drive 15 km, turn on and then its all working ok again.

My question is: Is there a (shrader type) valve under the pressostat switch
which allows it to be replaced without de-gassing the system? Can anyone
tell me for sure?

By the way, the evaporator has recently been replaced and this seems to be
(unfortunately) an unrelated problem.

Regards
Barry


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Old 12-07-2005, 09:01   #2 (permalink)
Mike F
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Posts: n/a
Re: Air Cond - 96 850

Baz wrote:
>
> Hi,
>
> I have reason to believe the air conditioner low pressure "pressostat"
> switch is intermittently faulty in my 96 Volvo 850. It is a non-climate
> control system. It has the correct charge (750g) and a gauge on the low
> pressure side seems to point to the switch being bad. The symptom is that
> sometimes the a/c will cool properly, 3deg C from the vents, with outside 33
> deg, and other times the compressor will only stay on for perhaps one
> second, and of course not cool at all. One instance of this, with the
> pressostat plug s/c, the compressor would start and with ambient over 40deg
> C, 15 deg C from the vents, and the suction line to the compressor is
> sweating but not freezing. With the pressostat in circuit, compressor short
> cycling. Drive 15 km, turn on and then its all working ok again.
>
> My question is: Is there a (shrader type) valve under the pressostat switch
> which allows it to be replaced without de-gassing the system? Can anyone
> tell me for sure?
>
> By the way, the evaporator has recently been replaced and this seems to be
> (unfortunately) an unrelated problem.
>
> Regards
> Barry


There is a (shrader type) valve under the pressostat switch. If you had
a pressure gauge on the low side, you should see the pressostat cutting
the compressor out in the range of 23-25 psi.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
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Old 12-07-2005, 14:01   #3 (permalink)
Baz
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Posts: n/a
Re: Air Cond - 96 850


"Mike F" <"mikef2316()"@allsttream.nett> wrote in message
news:43970C76.189AC2D4@allsttream.nett...
> Baz wrote:
> >
> > Hi,
> >
> > I have reason to believe the air conditioner low pressure "pressostat"
> > switch is intermittently faulty in my 96 Volvo 850. It is a non-climate
> > control system. It has the correct charge (750g) and a gauge on the

low
> > pressure side seems to point to the switch being bad. The symptom is

that
> > sometimes the a/c will cool properly, 3deg C from the vents, with

outside 33
> > deg, and other times the compressor will only stay on for perhaps one
> > second, and of course not cool at all. One instance of this, with the
> > pressostat plug s/c, the compressor would start and with ambient over

40deg
> > C, 15 deg C from the vents, and the suction line to the compressor is
> > sweating but not freezing. With the pressostat in circuit, compressor

short
> > cycling. Drive 15 km, turn on and then its all working ok again.
> >
> > My question is: Is there a (shrader type) valve under the pressostat

switch
> > which allows it to be replaced without de-gassing the system? Can anyone
> > tell me for sure?
> >
> > By the way, the evaporator has recently been replaced and this seems to

be
> > (unfortunately) an unrelated problem.
> >
> > Regards
> > Barry

>
> There is a (shrader type) valve under the pressostat switch. If you had
> a pressure gauge on the low side, you should see the pressostat cutting
> the compressor out in the range of 23-25 psi.
>
> --
> Mike F.
> Thornhill (near Toronto), Ont.
>
> Replace tt with t (twice!) and remove parentheses to email me directly.
> (But I check the newsgroup more often than this email address.)


Thanks , Mike, that's what I was hoping to hear. The pressostat control is
intermittent. When it works the pressure is correct. When it's playing up,
the compressor clicks in and out almost instantly. With it replaced by a
short circuit, the pressure is as expected. I still have to convince myself
it's not the connector pins having been spread and causing a bad connection
etc, but I can now replace the switch if that's needed without worrying
about opening the system, which is an additional hassle I didn't want.

Thanks,
Barry


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