Recharging A/C on '96 LH Car

I apologize for the length of this post in advance, but I'd very much
appreciate some guidance and wanted to share as many facts here as I thought
necessary to get good input from the experts in this group.

The A/C compressor on my son's 1996 Eagle Vision TSI (3.5L w/87K miles)
froze up over the winter. Other than melting and throwing the A/C belt, the
car ran fine over winter, but with summer coming we decided to replace the
compressor and the receiver/dryer. Although I own and have read the 1995
New Yorker/LHS/Concorde/Intrepid Factory Service manual (section 24 -
Heating and A/C and section 8W - electrical schematics), I can't find
answers to the following three basic questions:

1. How does one remove the receiver/dryer? I managed to get the two bolts
out that hold the bracket in place and had no trouble removing the 3/4"
flare fitting from the condenser. I also had no trouble removing the spring
clip on the "quick disconnect" (an oxymoron if ever I saw one!), but could
not manage to get the A/C line to detach from the receiver/dryer inlet flare
tube to expose the two O-ring seals. Specific instructions on how to
disconnect this would be very much appreciated since it appears that there
is a rubber seal that has hardened and appears to be stopping them from
coming apart..

2. I need to verify that I fully understand the electrical connections to
the new A/C compressor clutch since it is slightly different from the old
one and the connector wire color codes in the schematic do not appear to
agree with what I actually saw in the vehicle. After I got the old
compressor off, I noticed that it had two wires, one black and one white
going to the 2 pin connector/plug while the new replacement compressor had
one of the clutch activation wires grounded directly to the compressor
housing and only had a one wire connector. (By the way, this agrees with
what is shown in the FSM.) On the two wire (wiring harness side) connector
that mated to connector on the old compressor, there was a blue and a black
wire. When I checked these using an ohmmeter, it appeared as though the
black wire was directly connected back to the negative chassis ground, so I
wired that leg to the A/C clutch wire that was going to the compressor
housing ground. I then spliced the blue wire to the other (non-grounded)
lead on the compressor. I also removed the old small white rectangular
electrical device (possibly a diode based on the service manual and
schematic) and put it across the two leads on the new compressor clutch
since the new compressor did not come with this component.

Specific questions here are: Does the blue wire coming to that connector
provide the +12V feed to the clutch? Is the black wire actually grounded as
presumed by the .1 ohm measurement I took? And, lastly, what is the purpose
of the small white rectangular device across the old clutch and is it
required for the new one?

3. Once I get the above questions resolved, I'd planned to draw a vacuum on
the system, then let it sit overnight, and if no leaks are observed fill it
with R134a refrigerant. I have the vacuum pump and manifold gauge set and
have done this before successfully with other (non-Chrysler vehicles). In
those cases, I was able to simply short out the A/C pressure sensor switch
to activate the compressor and draw in the R134a through the low pressure
port. In this case, I see from the FSM that the pressure switch is actually
a "transducer" which appears to have three wires (+5V, signal out, and
0V/ground). The FSM specifically calls for a DRBII scan tool to mask the
transducer output and recharge the system. My question here is do I really
need the scan tool or is there a simple way to fool the controller into
activating the A/C clutch?

Thanks to all in advance for your thoughts here. At the moment my son took
the vehicle back to school so I will probably not get a chance to work on it
again for a couple more weeks, but I'd like to plan that out in advance
given these unforeseen issues that I had encountered which prevented me from
finishing the job last weekend. By the way, the compressor/clutch/pulley
assembly I purchased otherwise seems to be an identical match and came from
the factory with the correct type and volume of PAG lubricant and given that
the system was still pressurized, I do not believe I will need to add any
additional lubricant unless I succeed in getting the receiver/dryer
out/replaced as I had originally planned. (The FSM then would call for an
additional 1oz of PAG lubricant.)

Bob

 

Great question! I've done it twice. The manual just says "remove bolts and
take it off". The FSM's not the best on that job. Basically, you just need
to be a contortionest/acrobat/magician. There's not a procedure to it that
a person could explain using ASCII. It comes basically straight down with
extreme difficulty and moving the condenser around as much as possible.

The clutch itself is just an electromagnet. You almost couldn't go wrong,
but I agree with your thinking. I had the same experience, the replacement
compressors have the wrong plug on them, and I have to cut and splice them
in, noting which side is ground. Since the old compressor didn't have the
clutch grounded directly, I swear I think you could wire it up backward and
it would work exactly the same. But anyway, you did fine.

If you just hook a can up and let it charge, it'll pressure up the system,
and the compressor will come on eventually. If it doesn't, hook up a second
can after the first one's empty. You don't need the compressor running to
charge the system.

I find it's quite slow to get the cans to boil dry charging vapor. They
take forever. You can pour hot water on them if you get bored. You can
turn them upside down, too, and charge liquid, but if you do, I didn't
recommend it.

 

Never done it on that particular model. Sorry.

True- one wire goes to power, the other to ground. Polarity doesn't matter.

Well, you don't need the compressor running to START charging the system
from a vacuum, but to actually put enough refrigerant in for the system
to work the compressor must start. You should also set the controls to
FRESH AIR and MAXIMUM FAN SPEED. That will keep the compressor running
throughout the charging process. Otherwise it will cycle on and off and
slow down the process (at best) or overpressurize your can of
refrigerant as the low side pressure goes up with the compressor off (a
bad thing).

Not a good idea- liquid can "slug" the compressor (same thing as
hydraulically locking an engine) and break valves or other parts
internally. Best to charge as a gas with the can immersed in a bucket of
hot water to speed the process.


With respect to the need for oil- I suspect that the original compressor
failed due to lack of oil. It would not be surprising at all for a '96
LH car to have a very slow leak in the evaporator coil and for the oil
charge to slowly deplete there. Inspect the old compressor carefully- if
the inside of the outlet manifold has any metal flakes in it- you MUST
flush the whole system (not a bad idea anyway). If you can't get any oil
to dribble out of the old compressor, the system is dry and needs oil.

My recommendation would be to flush the system to get all old oil and
debris out, and then put a complete charge of oil into the new
compressor so that you know you have exactly the right amount of oil in
the system and its fresh oil.

 

Joe & Steve,

Thanks for the insight and recommendations.

Since no one addressed this, I presume the small white rectangular
electrical component across the A/C clutch is a protection diode of some
sort?

There was not much oil left in the compressor ... at least none dribbled out
when I momentarily had turned it over to check. There also were no obvious
metal flakes or debris in the manifold, but I did not tear the compressor
down to see the root cause of the failure, and since it's already been
tossed, I won't be able to do that now.

Based on your advice, maybe I will add a couple ounces of oil beyond what
came in the new compressor just for good measure.

If my son gets a few more years out of this vehicle then that is all I am
hoping.

Bob

 

If that's the case, then polarity will matter on any test hook up.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

I believe what you are referring to is a small capacitor of some sort to
absorb the voltage spikes generated from the compressor cycles off

Glenn

 

Yes, this could certainly be the case and would make sense, but if so, then
it is not shown in the FSM's electrical schematic.

 

Nope - I just looked at the schematic in the FSM.

Actually it is a zener diode. More correctly two zeners back to back.
What that means is that I wasn't 100% correct either - back to back
zeners mean that either polarity will work fine. If it was just a
single zener, then polarity would matter.

You are correct in that the purpose of the device (in this case, two
zener diodes in a single package) is to absorb the kickback energy
(technical term: back-emf) of the clutch turning off (to protect other
things in the electrical system from damage by voltage spikes).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

I just looked at the FSM schematics. See my other post, but bottom line
is that it contains two back-to-back zener diodes - so polarity doesn't
matter.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Bill,

I saw that in the FSM schematic and like you I am also a EE, so understood
this when I generically referred to the device as possibly "a protection
diode".

That said, I still am not certain that this is what it really is since it
does not look like a zener diode and has no markings that would indicate it
is as such. That was pretty much why I asked... I was simply curious since
I figured the diode shown on the schematic might also be inside the
compressor housing near the actual solenoid that engages the clutch
mechanism.

In any event, I did wire it exactly the same polarity wise as from where it
came. I just wondered if it was already in the compressor on the
replacement or if I needed to move it to the new one. At this point, I
think I did OK with that and it would have likely worked without it anyway.

Bob

 

Hi Bill...

That's *if* they both clamp at the same voltage, though.

Take care.

Ken

 

Ken,
There's no reason to think otherwise. As an electronics designer of
over 25 years, I can think of no other reason in that application other
than to make polarity an insignificant issue while still clamping the
spikes. If you can think of a reason to have a second opposite-polarity
zener - and of a different zener voltage, that would be good to know.
As it is, biasing the zener in the forward (non-zener) direction will
clamp at less than a volt (as a regular - non-zener - diode would).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Frankly, I question that it is a back-to-back Zener at all. back-to-back
zeners are generally used for inductive suppression of AC-powered loads,
not DC powered. I suspect the schematic drawer got it wrong.

You do not want reversed polarity on a DC system. In this kind of
setup, the clamp voltage on a back-to-back zener arraingement cannot
be lower than around 15 volts or the one zener would avalanche at
normal voltage in the system, and probably burn up. And applying
a reverse voltage of 15 volts to a DC system isn't a good idea, even if
the DC system is powered, particularly when it's being generated by
a collapsing electromagnetic field, which can dump quite a lot of
amperage for a short time.

It should be a normal diode, with polarity reversed.

Ted

 

Its a bi-directional zener diode. It is used to control induced voltage from
the magnetic field collapsing when the clutch is disengaged The diode
provides a path for the spike of about 200 volts. This protects the other
components in the system from voltage spikes.

Glenn

 

I don't disagree with anything you said. Just going by the schematic.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Ted,
With the back-to-back zener, the reverse (negative) voltage is at least
limited to the zener voltage (probably in the -15 to -20 volt range).
It is easier to design internal power bus protection for other
electronics in the system for -20 volt spikes than for -200 volt spikes.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')