how AC clutch cycles? AC thermostat checking?

Thu Jul 3 21:38:49 EDT 2003

I think I figured out my problem.  I did not verify it yet but I think that
permanently open fresh air door (broken hook on vacuum servo) causing low
temperatures at vents.
Compressor cycles when fan A/C fan is not on full speed and it does not when the fan
is on full.  I believe that continuos flow of warm air through evaporator is the
problem.  I will close the door and let you know what happened.

Thank you for your responses.
Konstantin.

Eric wrote:

> I don't have a Bentley for your car.  The closest I have is for an 88
> 5000.  That car had a full charge of 38 oz (1100 g) of R12.  From what I
> have been told and what has worked well in my experience R134a should be
> charged at 80 to 85% of R12.  This would mean about 31 oz of refrigerant
> or two cans and change.  You should always charge by wieght as pressures
> are used to trouble shoot problems and can have quite a variation just
> based on ambient temperature.
>
> Again according to an 88 5000 (YMMV) the high side should be around 170
> psi and the low around 20 to 25 psi.  It sounds like you charge is just
> fine and the pressures you are reading are good.  You vent temeratures
> are higher than I would expect (but not bad), but the lower your low
> side pressures get the lower your vent temperatures get.
>
> I think Peter is on the right track with checking the air flow over the
> condensor.  Does the AC cut out like this if you are driving down the
> highway or is it just when parked or moving slowly?  How long does it
> take before it starts running again?  I would find this strange with
> your vent temperatures, but is it possible your icing up the
> evaporator?  This would make the AC thermostat keep the compressor off.
>
> Is the compressor new?  Is it possible your clutch is flaky?
>
> Has this car ever had functioning AC for you?  It might also be a bad
> connection in a harness that once things heat up gives you trouble.
> Just looking at the 86 to 88 system it is 10 times more complex than say
> a GM system of the same era.  I am sure it is nice to use, but
> unfortuantly makes it a bit tricker to troubleshoot.
>
> The short version of all that babbling above is I think your charge is
> good and your trouble lies in either cooling of the condensor or a
> electrical/sensor gremlin.
>
> I wish you the best of luck.  I have been living and breathing (not
> literally) AC systems the last month trying to get our old cars cooling
> properly.  I know what it is like.  Summer swung in pretty quick here in
> Virginia.
>
> Eric Sanborn
>
> 85 4kq (R12 - Cold, but not as strong as Suburban)
> 88 Suburban (Recent R134a Conversion - vent temps 45 degress in 5
> minutes when it is 90 outside)
> 89 CRX Si (Older R134a Conversion - Good when moving, not when stopped)
>
> Konstantin Bogach wrote:
>
> >Measured  vent temperature today - 50F.   It is too low but I saw clutch
> >cycling.  What is most important to target - amount of refregirant or pressure?
> >
> >Konstanatin.
> >
> >
> >Peter Golledge wrote:
> >
> >
> >
> >>Konstantin,
> >>
> >>>From my limited experience you should be OK with 30 PSI on the low side.
> >>Did you have
> >>the radiator shroud panel in place?   Without this in place the rad fan wont
> >>do a good job
> >>cooling the condensor which in turn means the evap wont cool real well.  I
> >>would take the
> >>car for a spin with a temp gauge in the vents.
> >>
> >>Cheers
> >>--
> >>Peter Golledge.
> >>
> >>89 200TQA (R134A converted... cool)
> >>89 Saab 900i (R134A converted friggin freezing with no Cimate control)
> >>79 930 Porsche (R12 waiting on a conversion)
> >>87 LT1Q (No room for Aircon with the V8 motor in a 5K!)
> >>
> >>----- Original Message -----
> >>From: "Konstantin Bogach" <kbogach at comcast.net>
> >>To: "Eric" <eric-audi.ql at mindspring.com>
> >>Cc: <quattro at audifans.com>
> >>Sent: Saturday, June 28, 2003 8:55 PM
> >>Subject: Re: how AC clutch cycles? AC thermostat checking?
> >>
> >>
> >>
> >>>The only misbehaviour, as I suspected, was "no cycling" after 10 min of
> >>>running.  When compressor is on low pressure is 30-32 psi, high pressure
> >>>
> >>>
> >>is
> >>
> >>
> >>>around 200psi.  The only numbers for low pressure I saw was great Peter's
> >>>Golledge post about conversion procedure.  It states 30-35 psi is a norm.
> >>>
> >>>
> >>I
> >>
> >>
> >>>got there right after third can of R-134A.
> >>>
> >>>Konstantin.
> >>>
> >>>Eric wrote:
> >>>
> >>>
> >>>
> >>>>As far as how much charge weight of refrigerant is more important than
> >>>>pressure.  Recommendations I have heard put the charge of R134a at
> >>>>around 80% of an R12 charge by weight.
> >>>>
> >>>>I have never put my manifold on my Audi (still works great with R12) as
> >>>>I don't want to mess with a good thing.  I have seen the numbers for my
> >>>>Suburban when I converted it.  Its low side pressure cycles between
> >>>>about 55-60 psi when off down to 25 psi when the compressor cycles off.
> >>>>
> >>>>Have you had guages on it when it misbehaves to see if something is
> >>>>changing before it happens?
> >>>>
> >>>>-Eric
> >>>>
> >>>>Konstantin Bogach wrote:
> >>>>
> >>>>
> >>>>
> >>>>>Hi.
> >>>>>I just finished AC conversion.  The leak I reported 2 days ago was
> >>>>>probably due to not tight connection at manifold and not tight low side
> >>>>>shreder valve.  I took 3 cans of R-134A with low side pressure at 30psi
> >>>>>and refused to take more when I tried to  raise it to 35psi.
> >>>>>
> >>>>>Now the problem (may be not):  after 10 min working at 90F outside
> >>>>>clutch does not cycle.  Does it look normal?
> >>>>>
> >>>>>I removed thermostat, hooked up DMM  and it shows 1.3 Ohm.  Shouldn't
> >>>>>
> >>>>>
> >>it
> >>
> >>
> >>>>>be short (0 Ohm)?
> >>>>>
> >>>>>Thanks.
> >>>>>Konstantin.
> >>>>>200tqa '89  (now with cool air!!!)
> >>>>>200tq '89  (will have cool air soon)
> >>>>>S4 '93  (did not nose anywhere yet, and air is cool.  Wierd!)
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >
> >
> >
> >