95 850 turbo A/C - a different kind of problem

I have a 1995 850 turbo wagon, and I have read the discussions on
various problems with the air conditioning system, but I think my
problem is different.

This just started about a month ago, when driving in high altitude,
the a/c just gave up and started blowing (essentially) outside air. I
should mention at the time that we were occasionally opening the
windows to smoke, and it just seemed like the system got overwhelmed
by the humidity.

The next day, it happened again, under similar circumstances (it was
also 90+ degrees F outside). But later that night, it worked fine as
we drove across the state 350 miles home.

Since then, it has worked fine, until a trip on a hot, humid day
again. Then, we shut it off for half an hour, and turned it on again
and it worked fine (we have an automatic climate control, and we just
set the fan speed on "high" rather than "auto" which seemed to help).
Then, when it got too cold, I turned the fan from "high" to "auto" and
the A/C gave up again immediately, though the fan continued to run. I
did just recently replace the blower motor on the fan, and it is
working fine.

It strikes me that - even though we are getting no codes from the
system - there might be a problem with a switch or relay relating to
the automatic setting, as the A/C seems to work perfectly every time I
set it on high, but not on auto. Am I on the wrong track here, or is
this something?
South Dakota Tom

 

There's a couple of things that commonly cause these symptoms on 850s.

As the compressor clutch wears, the gap gets so large that when the
compressor clicks off, there is not enough magnetic force to pull the
clutch back on when the coil is energized. This can be cured by
adjusting the air gap (simple on a bench, not so easy in the limited
space on the car) or by wiring a relay into the circuit so the clutch
will get a higher voltage. (The S/V70 is wired this way.)

There is a switch on the back of the compressor that shuts it off if it
gets too hot. This switch seems to be set to too low temperature, and
has been eliminated on new compressors as well as the later cars. It's
mounted on the back of the compressor, simply disconnect the connectors
leading to it, and plug the 2 disconnected wires that are not part of
the switch into each other.

--
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.)

 

I have this same issue. Where exactly is the compressor and this
switch?

 

If you had plenty of air flow (just warm), then this may not apply.
Another thing that can cause A/C problems in 850s (mine's a '97)
is ice formation on the evaporator coil under the dash. This is most
likely in humid weather. Cooling becomes less and less effective,
and when the ice buildup becomes severe airflow is greatly restricted.
If the A/C is switched off (disabled) the air coming out of the vents
will still be cool for a while until the ice melts, then it becomes warm.

Running the fan at a higher speed than the auto setting is programmed
to do will help forestall the problem by raising the coil temperature.
(I think the auto fan settings are too low when the cabin temperature
is near the set point, probably due to excessive concern about noise.)

 

The compressor is the lowest driven accessory on the front (relative to
the car) of the engine. The switch is mounted on the back (non drive
end), the only thing back there with wires.

--
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.)

 

In addition as refrigerant is lost from the system it appears to operate
better except that the evaporator pressure is lower, and the temperature
colder, hence a more rapid build up of ice on the the evaporator surface
that leads to a cessation of cooling.

Another possibility is that the compressor clutch coil is overheating at
high load/high temperature and dropping out.

Bob