New AC Compressor a drag

  • Thread starter Thread starter blurp
  • Start date Start date
B

blurp

Hi All,

To set the stage I have a 1995 850 GLT Wagon (NA) with about 190km.

Friday evening (true to form) my AC compressor clutch seized. I
happened to have the hood open and saw it throwing sparks so I was
able to shut down before the belt was damaged. I got a remanufactured
compressor on Saturday and it was installed and holding pressure etc.,
the AC is blowing ice-cold again.

Trouble is that when the clutch kicks in it drops the RPM at low
speeds. At idle it seems as though it'll stall the engine.

The engine did stall under similar circumstances a couple of times in
the past two weeks but I didn't know why. After it failed I thought it
might have been the AC clutch and I was hoping that was a sign of
impending failure and that the new compressor would solve the problem.

Could it be a problem with the AC compressor or could it be the belt
is worn and slipping (and would that stall the car)?

Any suggestions as to what I might check or if something may have been
done wrong would be greatly appreciated. It may be that this is some
sort of break-in period so if that's common I'll be relieved.

Thanks,
blurp
 
In an earlier contribution to this discussion,
blurp said:
Hi All,

To set the stage I have a 1995 850 GLT Wagon (NA) with about 190km.

Friday evening (true to form) my AC compressor clutch seized. I
happened to have the hood open and saw it throwing sparks so I was
able to shut down before the belt was damaged. I got a remanufactured
compressor on Saturday and it was installed and holding pressure etc.,
the AC is blowing ice-cold again.

Trouble is that when the clutch kicks in it drops the RPM at low
speeds. At idle it seems as though it'll stall the engine.

The engine did stall under similar circumstances a couple of times in
the past two weeks but I didn't know why. After it failed I thought it
might have been the AC clutch and I was hoping that was a sign of
impending failure and that the new compressor would solve the problem.

Could it be a problem with the AC compressor or could it be the belt
is worn and slipping (and would that stall the car)?

Any suggestions as to what I might check or if something may have been
done wrong would be greatly appreciated. It may be that this is some
sort of break-in period so if that's common I'll be relieved.

Thanks,
blurp
Click to expand...

Isn't the idle speed control supposed to work (more or less) regardless of
load? I would expect the throttle/fuelling to be adjusted automatically to
take account of the AC clutch being engaged. Doesn't this happen? Did it
happen with the old compressor? Perhaps something hasn't been connected
properly to tell the engine management system that the AC is running?
--
Cheers,
Roger
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blurp said:
Hi All,

To set the stage I have a 1995 850 GLT Wagon (NA) with about 190km.

Friday evening (true to form) my AC compressor clutch seized. I
happened to have the hood open and saw it throwing sparks so I was
able to shut down before the belt was damaged. I got a remanufactured
compressor on Saturday and it was installed and holding pressure etc.,
the AC is blowing ice-cold again.

Trouble is that when the clutch kicks in it drops the RPM at low
speeds. At idle it seems as though it'll stall the engine.

The engine did stall under similar circumstances a couple of times in
the past two weeks but I didn't know why. After it failed I thought it
might have been the AC clutch and I was hoping that was a sign of
impending failure and that the new compressor would solve the problem.

Could it be a problem with the AC compressor or could it be the belt
is worn and slipping (and would that stall the car)?

Any suggestions as to what I might check or if something may have been
done wrong would be greatly appreciated. It may be that this is some
sort of break-in period so if that's common I'll be relieved.

Thanks,
blurp
Click to expand...

Try cleaning out your idle air control valve and throttle body, and make
sure the TB stop and idle needle valve are adjusted correctly. AC load will
vary depending on ambient temp, the ECU should automatically compensate.
 
Try cleaning out your idle air control valve and throttle body, and make
sure the TB stop and idle needle valve are adjusted correctly. AC load will
vary depending on ambient temp, the ECU should automatically compensate.
Click to expand...
Thanks for the suggestion! I'll check into it this evening once I
research what/where "TB stop and idle needle valve" are.

cheers!
B
 
blurp said:
Thanks for the suggestion! I'll check into it this evening once I
research what/where "TB stop and idle needle valve" are.

cheers!
Click to expand...

TB = throttle body. The stop is a setscrew, the needle valve is a black knob
on the underside.
 
James Sweet said:
TB = throttle body. The stop is a setscrew, the needle valve is a black
knob on the underside.
Click to expand...

No knob / needle valve on an 850!!

Tim..
 
Oops, for some reason I was thinking this was a 240.
Click to expand...

Well I've been driving and monitoring the behaviour of the compressor
and the near-stalling has stopped happening. The weather has been
consistently hot and humid necessitating AC on even the shortest
drives and since yesterday the problem seems to have cleared itself
up.

Perhaps the computer has reset itself or "learned" the compressor load
to adjust to it. Or perhaps the throttle body or idle air control had
a spot of schmunge that has burned off/blown away/melted. Or perhaps
it's Volvo gremlins at work while I sleep.

If the problem comes back I will inspect more closely. I know the
engine was power-washed after the work was done... maybe it was just
something that got wet that needed to dry out.

Thanks for your quick advice (again).
blurp
 
blurp wrote:
Well I've been driving and monitoring the behaviour of the compressor
and the near-stalling has stopped happening. The weather has been
consistently hot and humid necessitating AC on even the shortest
drives and since yesterday the problem seems to have cleared itself
up.

Perhaps the computer has reset itself or "learned" the compressor load
to adjust to it. Or perhaps the throttle body or idle air control had
a spot of schmunge that has burned off/blown away/melted. Or perhaps
it's Volvo gremlins at work while I sleep.

If the problem comes back I will inspect more closely. I know the
engine was power-washed after the work was done... maybe it was just
something that got wet that needed to dry out.

Thanks for your quick advice (again).
blurp
Click to expand...

Actually, it's not out of the question that the computer has "learned"
how the engine should act. Your throttle openings (and thus air flow or
manifold pressure, whichever is measured on your engine) are different
now with the AC on. It usually takes a hundred miles or two for the
kinks to work themselves out as the ECM remaps. This is especially
likely if the weather is significantly different (hotter!) than it was
when the AC failed in the first place or if several hundred miles have
passed since it worked last.
 
blurp wrote:


Actually, it's not out of the question that the computer has "learned"
how the engine should act. Your throttle openings (and thus air flow or
manifold pressure, whichever is measured on your engine) are different
now with the AC on. It usually takes a hundred miles or two for the
kinks to work themselves out as the ECM remaps. This is especially
likely if the weather is significantly different (hotter!) than it was
when the AC failed in the first place or if several hundred miles have
passed since it worked last.
Click to expand...

Well there has been trouble-free operation except one incident a few
days ago when I was accellerating up a hill (not just idling) and the
engine started giving out like the fuel pump was failing. I flicked
off the AC switch and full power was restored and everything was fine.
I turned the AC back on a few minutes later and again no troubles
since.

Weird.

blurp
 
blurp said:
Well there has been trouble-free operation except one incident a few
days ago when I was accellerating up a hill (not just idling) and the
engine started giving out like the fuel pump was failing. I flicked
off the AC switch and full power was restored and everything was fine.
I turned the AC back on a few minutes later and again no troubles


Weird.

blurp
Click to expand...

Basically, the way this works is that there are combinations of airflow
(or manifold pressure) and temperature. Think of a grid with airflow
values across the top and temperature values up and down the left side.
In each box is a value. The value represents the starting injector
pulse width for that combination of temperature and flow (or pressure).
The initial value is adjusted using feedback from the O2 sensor(s).
The O2 sensor feedback loop is fairly fast but not instant. As the
adjustment is made to the injector pulse width, the value in the box is
changed.

This is sometimes called the "mapping" of the engine's operating
conditions by the computer.

(This is an oversimplification. In reality RPM is also considered. But
it suffices to illustrate the concept.)

With the AC on, the throttle opening (and thus the airflow or pressure)
changes. This puts you into different boxes that might not be used
during operation without the AC very often. Those boxes now contain the
wrong initial values for operation with the AC on. The computer will
adjust but it has to hit all the boxes you'll notice before the car
seems to run well.

This also happens after an ECU reset. Typically (for me, anyway) this
takes a couple of days and over a hundred miles. YMMV...but if this is
what's happening (I can't be sure at all), then it should continue to
improve and eventually run right. If it takes over a week or 300 miles,
there is most likely a real problem of some sort and not just the
computer remapping.

JRE
 
Hi All,

To set the stage I have a 1995 850 GLT Wagon (NA) with about 190km.

Friday evening (true to form) my AC compressor clutch seized. I
happened to have the hood open and saw it throwing sparks so I was
able to shut down before the belt was damaged. I got a remanufactured
compressor on Saturday and it was installed and holding pressure etc.,
the AC is blowing ice-cold again.

Trouble is that when the clutch kicks in it drops the RPM at low
speeds. At idle it seems as though it'll stall the engine.

The engine did stall under similar circumstances a couple of times in
the past two weeks but I didn't know why. After it failed I thought it
might have been the AC clutch and I was hoping that was a sign of
impending failure and that the new compressor would solve the problem.

Could it be a problem with the AC compressor or could it be the belt
is worn and slipping (and would that stall the car)?

Any suggestions as to what I might check or if something may have been
done wrong would be greatly appreciated. It may be that this is some
sort of break-in period so if that's common I'll be relieved.

Thanks,
blurp
Click to expand...

Hi Blurp,
What are the steps to replacing a A/C Compressor? My clutch is not
kicking in
and I need to replace the Compressor. I did the blower motor last
week, so now I
think I can do about anything.
Thanks,
Joseph
 
Basically, the way this works is that there are combinations of airflow
(or manifold pressure) and temperature. Think of a grid with airflow
values across the top and temperature values up and down the left side.
In each box is a value. The value represents the starting injector
pulse width for that combination of temperature and flow (or pressure).
The initial value is adjusted using feedback from the O2 sensor(s).
The O2 sensor feedback loop is fairly fast but not instant. As the
adjustment is made to the injector pulse width, the value in the box is
changed.

This is sometimes called the "mapping" of the engine's operating
conditions by the computer.

(This is an oversimplification. In reality RPM is also considered. But
it suffices to illustrate the concept.)

With the AC on, the throttle opening (and thus the airflow or pressure)
changes. This puts you into different boxes that might not be used
during operation without the AC very often. Those boxes now contain the
wrong initial values for operation with the AC on. The computer will
adjust but it has to hit all the boxes you'll notice before the car
seems to run well.

This also happens after an ECU reset. Typically (for me, anyway) this
takes a couple of days and over a hundred miles. YMMV...but if this is
what's happening (I can't be sure at all), then it should continue to
improve and eventually run right. If it takes over a week or 300 miles,
there is most likely a real problem of some sort and not just the
computer remapping.

JRE
Click to expand...


Wow, that is both fascinating and informative. It appears that what
has been happening is exactly as you describe it. Since that last
posting I have had no stalls or problems. The last time was under a
somewhat unusual load condition (a steep hill climb from a virtual
standstill) and it makes sense that the expected value in that part of
the "map" would not often be called on.

By remedying the problem by shutting off the AC, however, have I
somehow interrupted the re-mapping process by returning conditions to
match the expected value rather than allowing the computer to "learn"
the new conditions?

Like I said it seems to be running great now but my wife is a bit
hesitant to drive the car in case it starts "acting weird".

Thanks for the descriptive info!
blurp
 
Hi Blurp,
What are the steps to replacing a A/C Compressor? My clutch is not
kicking in
and I need to replace the Compressor. I did the blower motor last
week, so now I
think I can do about anything.
Thanks,
Joseph
Click to expand...

Sorry, Joseph, I didn't do the work myself. I would say, however, that
you need to be VERY cautious with this job because even a seemingly
discharged system may be hiding a very highly pressurized section
(400+psi) which can release somewhat violently as you disconnect the
compressor and spray you with oils, dyes, and refrigerants, all of
which are likely pretty toxic. You don't want to get that stuff in
your eyes.

Also, once you get it all together you need to have the proper AC
vacuuming and charging equipment (you can't just do it with a few cans
of RedTech). In all I think this may be one of the least
"do-it-yourself"-friendly jobs you can tackle.

Good luck,
blurp
 
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