2002 LW300 A/C clutch

I can't seem to activate my A/C clutch. When I turn on the switch with
engine idling, there is a slight increase in RPM, which is normal, and
indicates the switch is working. I tested the relay (switched with the horn
relay) and it is working fine. The 10A fuse is not blown. Would the A/C
diode 'fuse' cause this problem? I wouldn't think so. I don't know how to
test the diode, but I found it doesn't have continuity, which I suspect is
normal. Anyone know how to check the diode? If the diode is OK, are there
any other things to check before testing the clutch itself? What is the best
way to test the clutch?

--
Dana

In terms of timetables, as quickly as possible-whatever that means."-On the
president's time frame for shoring up Social Security, Washington D.C.,
March 16, 2005

The diode is just to protect the electronics from the 'inductive kick' of
turning off the clutch electromagnet. Many digital voltmeters have a diode
test function but with most simple ohmmeters, the diode may test open.
Biggest problem is if the diode is shorted. (diodes are supposed to pass
current in one direction only)
Pull the connector at the clutch and test with an ohmmeter for continuity
first. Should be something like 10 Ohms (just off the top of my head). If
there is no continuity, the coil is open and the clutch needs to be
replaced. If there is continuity, get some jumper leads and ground one side
of the clutch coil. Connect the other lead to battery+. (engine is off for
this test). Clutch should activate and pull in the armature. If the clutch
still does not activate, the gap between armature and stator is too much and
the clutch needs to be replaced. If it does pull in, check further back in
the electronics.
Hope this helps.
Oppie (2001 LW300)

ps - I have the 00-01 shop manual if you need any diagrams.

"Dana Rohleder" > wrote in message
...
>I can't seem to activate my A/C clutch. When I turn on the switch with
>engine idling, there is a slight increase in RPM, which is normal, and
>indicates the switch is working. I tested the relay (switched with the horn
>relay) and it is working fine. The 10A fuse is not blown. Would the A/C
>diode 'fuse' cause this problem? I wouldn't think so. I don't know how to
>test the diode, but I found it doesn't have continuity, which I suspect is
>normal. Anyone know how to check the diode? If the diode is OK, are there
>any other things to check before testing the clutch itself? What is the
>best way to test the clutch?
>

Thanks! Next question, could there be something else locking it out - for
instance, the ambient temperature switch malfunctioning or the switch that
disengages the clutch on hard acceleration, or is that all done by the ECM?

--
Dana


"Oppie" > wrote in message
news:1114003335.dec099798ac98d7390c27bb8dec28ac0@t eranews...
> The diode is just to protect the electronics from the 'inductive kick' of
> turning off the clutch electromagnet. Many digital voltmeters have a diode
> test function but with most simple ohmmeters, the diode may test open.
> Biggest problem is if the diode is shorted. (diodes are supposed to pass
> current in one direction only)
> Pull the connector at the clutch and test with an ohmmeter for continuity
> first. Should be something like 10 Ohms (just off the top of my head). If
> there is no continuity, the coil is open and the clutch needs to be
> replaced. If there is continuity, get some jumper leads and ground one
> side of the clutch coil. Connect the other lead to battery+. (engine is
> off for this test). Clutch should activate and pull in the armature. If
> the clutch still does not activate, the gap between armature and stator is
> too much and the clutch needs to be replaced. If it does pull in, check
> further back in the electronics.
> Hope this helps.
> Oppie (2001 LW300)
>
> ps - I have the 00-01 shop manual if you need any diagrams.
>
> "Dana Rohleder" > wrote in message
> ...
>>I can't seem to activate my A/C clutch. When I turn on the switch with
>>engine idling, there is a slight increase in RPM, which is normal, and
>>indicates the switch is working. I tested the relay (switched with the
>>horn relay) and it is working fine. The 10A fuse is not blown. Would the
>>A/C diode 'fuse' cause this problem? I wouldn't think so. I don't know how
>>to test the diode, but I found it doesn't have continuity, which I suspect
>>is normal. Anyone know how to check the diode? If the diode is OK, are
>>there any other things to check before testing the clutch itself? What is
>>the best way to test the clutch?
>>
>
>

The most common cause of this symptom is low refrigerant. The AC compressor
is protected by a low pressure cutout switch which prevents the clutch from
activating if the pressure is too low so that the unit does not self
destruct by running without sufficient refrigerant. I do not know about
this model Saturn, but many times you can pull the pressure cutout switch
connector and jumper across the contacts and then see if the clutch engages.
If it does, then do not run it more than a few seconds. It means the system
is leaking or (less probable) that the switch is bad.

Good luck and report what you learn for others to benefit.

Bob

"Dana Rohleder" > wrote in message
...
> Thanks! Next question, could there be something else locking it out - for
> instance, the ambient temperature switch malfunctioning or the switch that
> disengages the clutch on hard acceleration, or is that all done by the
ECM?
>
> --
> Dana
>

True, Low refrigerant pressure can cause the evaporator to ice up (or worse)
so there is protection for low gas pressure. There should also be either a
superheat sensor or an ambient temperature sense somewhere that will shut
down the compressor below a certain temperature to protect it. Low ambient
temperatures might cause liquid refrigerant to be returned to the
compressor. That both dilutes the oil in the compressor sump and can destroy
the compressor if the liquid is pulled into the cylinders. (just like water
ingestion will kill a running engine...you just can't compress a liquid). By
design, the liquid refrigerant is supposed to all boil off into gas in the
evaporator and return only gas to the compressor.
Thankfully, my lw300 has been running well and I haven't gotten into the
specifics of the sensors
..
"Bob Shuman" > wrote in message
...
> The most common cause of this symptom is low refrigerant. The AC
> compressor
> is protected by a low pressure cutout switch which prevents the clutch
> from
> activating if the pressure is too low so that the unit does not self
> destruct by running without sufficient refrigerant. I do not know about
> this model Saturn, but many times you can pull the pressure cutout switch
> connector and jumper across the contacts and then see if the clutch
> engages.
> If it does, then do not run it more than a few seconds. It means the
> system
> is leaking or (less probable) that the switch is bad.
>