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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..

  1. 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?

  1. 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

Reply to
Bob Shuman
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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.

Reply to
Joe

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.

Reply to
Steve

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

Reply to
Bob Shuman

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')

Reply to
Bill Putney

refrigerant

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

Reply to
maxpower

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.

Reply to
Bob Shuman

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')

Reply to
Bill Putney

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')

Reply to
Bill Putney

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

Reply to
Bob Shuman

Hi Bill...

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

Take care.

Ken

Reply to
Ken Weitzel

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')

Reply to
Bill Putney

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

Reply to
Ted Mittelstaedt

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

Reply to
maxpower

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')

Reply to
Bill Putney

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')

Reply to
Bill Putney

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