'96 850 A/C compressor over temp sensor/switch?

Where exactly is the A/C compressor over temp sensor/switch on a '96
850?

I've had the problem others have been complaining about:

A/C blows cold for 10-20 minutes but then starts blowing normal hot air.

Local Volvo mechanic said basically that it means the compressor is
going bad and that it would cost about $400 to replace it with a used
one. Since summer is almost over I told them I'd wait until next year.

However if it is just bad sensor, and is easy to by-pass, I want to give
it a try now while it is still hot. I've read lots of posts about this,
but I have no idea where this sensor is and how exactly to by pass it.

Is there anywhere on-line that has pictures of where in the engine bay
it is located and what needs to be done?

Any help would be greatly appreciated, especially from any of you who
have tried this yourselves. Did it work?

Thanks!

 

The AC system is not only used in the summer time, but quite a bit in
the winter time as well. Every time you turn on your defrost you are also
turning on the AC system. Defrost does not simply blow warm hot air on your
windshield, it blows dehumidified warm air on your windshield. An
imporoperly running AC system will drastically decrease your ability to
maintain a "fog" free windshield in the colder months.
Bypassing the switches are not a viable option either. By bypassing the
low pressure or high temp you can increadibly damage a system. You could
introduce air and water which will result in acid or you can blow out a
condensor, evap, line or any other portion of the system.
Did this tech put gauges on it? That's really the only way to tell
what's causing the premature cycling of the system. A defective compressor
will not allow it to run cold at all.

-Brian

 

Well thats the thing they basically made it sound like they know from
experience that the compressor is bad. The owner of the shop even said
something like: We've spent so much time in the past chasing this or
that with the A/C's that it is easier and cheaper in the long run
replace the compressor. It isn't the evap since it does blow cold.

 

OK, the evap gets cold, that tells us 2 things...1, that the compressor is
running and the valve plates internally should be OK (not that they are
perfect but OK). 2, that the system is not under charged. If it was under
charged it would not be getting cold at all.

That leads us to 2 common things that could cause the system to shut off;
1, High temp, could be caused by a blocked condensor, not in the
refridgerant side but where the air passes thru or a bad condensor fan motor
or controls (if it has one).
2, High ref charge which is always possible when someone that doesn't have
the proper tools or training works on an AC system.

So before you pay the yokels to give you a used compressor bring it to a
reputible repair shop and have the system check properly rather than the
"we've seen so many of these that it's got the be the compressor" answer.

It could be something as simple as a 30$ fan switch.

If your in the Boston area I can recomend an awesome mechanic who does work
on the side from his regular shop foreman job at a local stealership.

-Brian

 

I believe the issue is with the notorious compressor overtemp switch; there
have been recent threads about it. The proper fix is usually to bypass it
because it never seemed to do any good - just shut down perfectly healthy
systems.

Mike

 

Hi Mike,

I haven't seen the threads, just found the group actually. I did a few
searches and see that they have removed this switch in newer models. Most
everything I have found blames it on the gap of the clutch as opposed to
being a "defective switch"...I can see that happening...little slippage
generates a whole heck of a lot of heat which can transfer to the body of
the compressor where the switch is located.
I still stand by my previous replies though, only real way is to throw
the gauges on, not simply replace the compressor.

-Brian

 

Michael - right I remember reading about this in the previous threads.
Hence my original post asks WHERE is this overtemp switch and how
exactly do I by pass it? From the old threads it seems like it should
be easy to do, but I don't know even where in the engine bay to be
looking, and what to be looking for, and what to unplug, replug, change
etc...

That is the information I need...

-Atif

 

Brian -

If I just by pass the overtemp switch, can anything really bad happen?
As I see it in a worse case scenario the lack of a switch causes the
compressor to really go bad...but I'm looking at replacing it anyways.

I occasionally do travel to Boston so if you have the name of a person
please let me know.

You can email me at:

atif *AT* myrealbox.com


just put "VOLVO" in the subject title as I normally just delete all the
email in that account without looking at it.

If the switch was take out in later models, it can't be all that
important, can it?

-Atif

 

Hi Atif,

I sent Dave (the mech) an email with your contact info.

As far as the switch, it's on the compressor body itself. It should be the
only electrical part on the body. The clutch also has 2 wires going to it,
but you'll easily be able to differentiate between the 2. Simply follow the
sensor leads back to the connector,unplug it, fashion up a jumper, weather
proof it and your done. What damage it can cause...well if the sytem is
operating properly and it is simply a defective switch then nothing bad will
happen. If it's not whats causing your AC to cycle then it'll continue to
happen.

I'd still prefer to see gauges on it!

-Brian

 

No need for a jumper on my 94. It was wired like this:

CLUTCH--------->>------SWITCH------>>---------CAR

After disconnecting the switch, I had two connectors, male and female.
I just let them do what comes naturally, and ended up with this:


CLUTCH--------->>---------CAR

Each connector had a plastic weather cover over it. I used one of
them to protect it and keep them from becoming unplugged.

To reply, please remove one letter from each side of "@"
Spammers are VERMIN. Please kill them all.

 

OK, dig out my trusty old fits-anywhere Coolpix-950 and a trouble
light, and...

1. Overall view. The area of interest is in the circle, just below
the alternator:
http://webpages.charter.net/dwarner2/Overview.jpg

2. The switch connectors are plugged together and set in the clip to
the right to keep them out of the way. The clutch to harness
connector pair fits in the clip to the left.
http://webpages.charter.net/dwarner2/Connectors.jpg
It's a VERY tight fit down here.

3. A shot of the back end of the compressor. The switch itself is not
visible, since it's near the bottom. This is just to show the switch
wires and sleeve that covers them. Shot from the upper right of the
compressor, looking down:
http://webpages.charter.net/dwarner2/BackEnd.jpg



To reply, please remove one letter from each side of "@"
Spammers are VERMIN. Please kill them all.

 

A/C blows cold for 10-20 minutes but then starts blowing normal hot air.

Crap. Quite likely, if it's very hot there it could be the clutch gap
which is too large. You just need to remove the clutch pulley and
remove the right number of shims to get it back to the right spacing.

Mine measured 1.2mm gap when it should be 0.3 to 0.6mm max. Works a
treat now.

The only thing is that to get to this, I found I had to remove the
engine ECU and box, the power steering pump, the alternator, all the
bracketry etc.

David.

 

Michael - right I remember reading about this in the previous threads.

The actual switch is at the bottom, behind the compressor, don't be
mistaken by the object with wires that is on the top at the front.

David.

 

Many thanks, Doug, for the pictures of the switch connections.

I just went out and disconnected mine. You were right, it is TERRIBLY
difficult to get to and I scraped up my forearms pretty well. I'll get back
to the group and let y'all know if it fixes the
turning-off-after-ten-minutes-problem.

As to the suggestions of hooking up pressure gauges and other fancy
diagnostic equipment, it doesn't seem necessary to me. It's obvious that
the clutch is not engaged when the system stops working after ten minutes.
I know it's not the controller or the sensor because the fan keeps running
full tilt.

Now maybe it is the clutch adjustment that's CAUSING the overheating that's
causing the overtemp switch to open, in which case I'll probably burn out
the compressor in the months to come, but I'm willing to take a chance on
the easy fix for now, rather than risk really breaking something in trying
to remove the compressor to adjust the clutch shims.

-----

-RL

OK, dig out my trusty old fits-anywhere Coolpix-950 and a trouble
light, and...

1. Overall view. The area of interest is in the circle, just below
the alternator:
http://webpages.charter.net/dwarner2/Overview.jpg

2. The switch connectors are plugged together and set in the clip to
the right to keep them out of the way. The clutch to harness
connector pair fits in the clip to the left.
http://webpages.charter.net/dwarner2/Connectors.jpg
It's a VERY tight fit down here.

3. A shot of the back end of the compressor. The switch itself is not
visible, since it's near the bottom. This is just to show the switch
wires and sleeve that covers them. Shot from the upper right of the
compressor, looking down:
http://webpages.charter.net/dwarner2/BackEnd.jpg



To reply, please remove one letter from each side of "@"
Spammers are VERMIN. Please kill them all.

 

I do not see any reason to put a used compressor on the vehicle. At
least install a rebuilt unit. The cost of labor, recharging the system,
etc. make the installation of a used unit which might fail the next day
seem rather foolish. For example, www.rockauto.com lists a rebuilt
compressor at about $350 for the part.

No way would I install a used compressor, assuming that it indeed need
replacement.

John

 

Now maybe it is the clutch adjustment that's CAUSING the overheating that's

Not at all. The clutch not engaging means that the AC isn't functioning
period. There's nothing that's going to overheat in that state.

David.

 

Right, I think he said "used" and meant "rebuilt" (as opposed to a brand
new one). I don't think they would actually recommend putting a used
part like that into the car. That is the sort of thing that I would
grill them about if I o.k.'d the work...

Where did you get the rebuild, does it have any warranty, etc etc...

Thanks,
-Atif

 

this doesn't sound bad....however...

This is the part that I'd be worried about since I really don't have
that much experience working on cars...

 

I'm going to try this tomorrow, thanks for the warning about the
forearms...I'll be sure wear an old long sleeve shirt or something!

 

WOW! This is *EXACTLY* what I needed! THANK YOU!

There is just NO WAY I would have been able to figure out where this
stuff is and what I should be looking for without these pictures.

I'll try this either this afternoon or Monday morning and let you all
know if it works. This weekend I've been driving around and sure enough
it works great for like 10-15 minutes and then just starts blowing warm
air. I've leaving this week for a long drive so if the A/C works the
whole drive I'll be psyched!

Thanks again!

-Atif