Diagnosing 1996 RMW a/c not working=Upset spouse!

This may not be in the correct catagory, but I figured more folks read this one! If not in the right one-Sorry, and should I go to electrical or interior? Anyways, the A/C was working intermittently (compressor worked when it wanted to) but now has given up altogether. I tried unplugging the electrical connector and jumping with a paper clip, but compressor doesn't come on-although jumping seems to make a slight diifference in rpm's. I just read thru the HVAC code reading part and will that give me a code to indicate where I should start looking? When I put the digital control on the A/C setting the secondary fan does not turn on either. Any thoughts? I do have an OBD2 scanner-not sure if that will give me A/C related codes? I only have the Haynes repair manual and it really doesn't go into A/C diagnostics very far! I live in the DFW area and am willing to drive for help! I really don't want to get bent over with repairs on this--Thanks for the assistance!-Steve

Steve - First Pressure Check the system to see if it has freon in it.

https://www.youtube.com/watch?v=lqHzI59QyLA&feature=player_embedded

https://www.youtube.com/watch?v=Wn0C9jPOAAQ&feature=player_embedded

Sorry, I knew there was something else I forgot to mention on the post! We checked with decent a/c gauges and there was supposedly the correct amount of freon in the system. I also visually checked and reseated all the fuses for grins but no results!

Hey 1phattsswagon--thank-you for the suggestion--informative videos also! Now if I could find someone with a known accurate set of gauges!!

how many miles on the car? I had my 94s compressor go out around 150 ish.
The compressor just quit, no sparks, whining or anything. system still had pressure.

If so, you'll need to flush out the lines.
http://www.ackits.com/c/BlackDeath/Auto+AC+Compressor+Failure+%28Black+Death%29.html

I did the whole system myself 2.5 years ago with no problems. As the site says do it right the first time or do it twice.

Not sure if this was the company I used or not.

Well, this was interesting--I just went out and turned A/C on-same result-nothing happening. But I decided to touch the compressor clutch and low and behold-the compressor kicked in!! A/C was starting to work!! So, what's the opinion? Can the clutch be replaced or do I break down and get new compressor and all the stuff it will need for the replacement? (I don't have the big bucks right now)-Oh, and BTW, the car has 230k on it. Thanks!

Sounds like you may have a sticking compressor relay.How well is it cooling now?

or a worn out clutch surface. That's a lot of miles. I know that the clutch gap is very small & critical. As the clutch material wears away, the gap gets larger until it's too big for the electromagnet to suck it in. If it were me, I'd install a brand new compressor if you plan on keeping the car.

Taps442 wrote:

But I decided to touch the compressor clutch and low and behold-the compressor kicked in!! A/C was starting to work!! !

you touched the clutch and it started to work,........ magic.

If its working it doesn't need to be fixed,.

what was the question again?


Nick

^^^or, yeah!... If it's stays working... litfa.

I have always been the type to try and do the job correctly the first time, so I will start saving up for new compressor, o-rings, accumulator and the orifice tube. It would probably be temporary fix to just do the clutch-but it would work with my pocket book better right now! The beast does have some miles on her so she desrves new!

I do like the "if it's not broke theory", but it is the wife who enjoys and expects cold air! And we all know if mama is happy, everybody's happy! I don't want to get the phone call when she is driving from Texas to Chicago telling me the car has no A/C--that would get brutal!

someone on the other forum did the clutch only. It was a PITA and then the compressor quit a couple of months later. Apparently they aren't too easy to R&R unless you have the right tools for the job and the cost difference when all said an done probably isn't enough of a difference to roll the dice. I would take Nick and Jimbeaus advice and let it die a natural death and then replace. Might just have to pop the hood and help it now and again.

that said if Mama taking a road trip, fix it now!

Most of you know that it can be tough to even get our spouses to drive these older, more unique vehicles. Mine actually tells others that she loves to drive it! And I think she enjoys the looks she gets from people in their new cars, and the thumbs up!

Taps442 wrote:

Well, this was interesting--I just went out and turned A/C on-same result-nothing happening. But I decided to touch the compressor clutch and low and behold-the compressor kicked in!!

Common problem, cheap and easy fix: remove the clutch and remove a shim to reduce the gap. You don't even have to open the system. Do you have a FSM?

Edit: Actually, if that is an HD6 compressor, it's an even easier fix: no shims. The clutch is a press fit. You just need the tool to adjust the air gap. Slide a business card in the gap and snug in the clutch until it just touches the card. You may be able to borrow the tool from your local auto parts chain.

Hmmm-I'm not familiar w/ FSM? What is it?

Factory service manual. If u don't have one some one on hear would probably be able to look up what u need. I have 91,92, and 94 sets... But 96 may have some minor differences

Definitely don't have any Factory service manuals for the Buick-I know I need to get some though!

The Buick FSM's are more expensive and constructed of better materials than the Chevy FSM's.

No matter. It has pretty pictures though.

Assuming it's a Harrison 6 cylinder compressor with a press-fit clutch (meaning the hole in the clutch is a few thousandths of an inch smaller than the shaft of the compressor) then the shaft has a threaded hole and the clutch has a threaded hole. The tool is in 3 pieces. The body has internal and external threads -- the external threads match female threads in the clutch. The center bolt of the tool is threaded to match the tool body, and there is a presser foot that attaches to the end of the bolt.

To remove the clutch, the tool is assembled with the bolt retracted so the foot is next to the body. The body is screwed into the clutch and held with a wrench while the bolt is wound in with a second wrench. The foot contacts the compressor shaft and the clutch is drawn off the shaft as the bolt is cranked in. As the clutch is pulled off, the gap between the clutch and the pulley increases. (That's also usually when the shaft key falls into the accumulated greasy road dirt coating the frame under the oil pan.)

EDIT: you don't even have to remove the fan belt to do this.


To install the clutch (or reduce the gap) the tool is reversed. The presser foot is removed from the bolt and the bolt screwed into the compressor shaft. The bolt is then held still with a wrench and the body of the tool turned with the other wrench to press the clutch onto the shaft. (that's usually when you remember to reinstall the shaft key that fell out earlier...)

The FSM will have the exact specs for the clutch gap. (The Buick version comes with a pretty girl to read the specs to you, well worth the extra $$$, IMHO). However, the rule of thumb guide is that a folded business card shouldn't fit but a single business card should slide in.

The clutch is of course an electromagnet. If the gap is OK then it is possible that a bit of corrosion is reducing the available voltage or even that the charging system isn't quite up to snuff and the battery voltage is low. But usually the gap just needs a bit of adjusting.

Nothing lasts forever, but the AC compressor is actually pretty reliable provided the system is properly maintained with the proper charge of refrigerant. The refrigerant is what carries the lubricating oil around the system -- if the charge is low, the compressor gets starved for oil and that ain't good for it! Even a genuine Buick FSM can't save it then. (Too much refrigerant is not good either, especially if it is so overcharged that liquid makes it to the compressor intake -- the system should be evacuated and charged by weight when it's time for a top-off). Moisture (from failing to fully vacuum the system after service) is the other way of quickly killing the compressor.

what if the business card is laminated?

Thanks for the detailed instructions on checking the clutch gap! I will check and maybe get a temporary fix till I can replace stuff. Do we know how much freon the system takes from empty? (It is R134)-Thank goodness!

I'm at work so can't pop my hood, but use the amount shown on the underhood sticker. "empty" means empty of air too.

I wouldn't start tearing into it until you have ruled out lack of electricity to the compressor. The first thing I would do (as was suggested to me once) is to disconnect the battery for a couple of minutes..... reconnect, then turn the ignition key on and watch the climate control panel do a countdown. When it's done, everything is reset and MAY be fully operational again! If that doesn't work, you should hook up your gauge set, turn the panel to coldest A/C and fan (engine running) and try a couple of things to energize the clutch..... First, try jumpering the pressure switch plug with a paperclip. If this works, read the gauges and if the high is below 200 and the low is less than 10, you need to add freon. If the High is over 400, the switch was doing it's job by cutting off the electricity, and you should quickly pull the paperclip before something blows!
If jumpering the switch plug fails to deliver 12 volts to the compressor, check the plug for voltage (should be 12)
For purposes of checking for low freon charge, you can run a jumper wire from pos batt post to the clutch wire and check your gauges. If they read 200-350 high (red gauge) and 14-50 on the low gauge (green) your problem is electrical. With these reading while the compressor is running, you should have cold A/C

AzDon wrote:

I wouldn't start tearing into it until you have ruled out lack of electricity to the compressor

He did that in post #6. You must have missed it -- he tapped on the compressor clutch and it engaged. Your advice is sound for the initial post about intermittent operation.

I'd like to comment on some of your other points, if I may:

Quote :

The first thing I would do (as was suggested to me once) is to disconnect the battery for a couple of minutes..... reconnect, then turn the ignition key on and watch the climate control panel do a countdown. When it's done, everything is reset and MAY be fully operational again!

There are some cars that will lock out the AC system if the HVAC module detects a low pressure signal. The Roadmaster is not one of those cars. The LP switch is part of the CCOT system and deliberately cuts in and out to regulate the evaporator temperature. The PCM cuts out the clutch if the tranducer reports a pressure of less than 0 or greater than 430psi. However, as soon as the condition is corrected, the PCM will again energize the clutch.

Quote :

If that doesn't work, you should hook up your gauge set, turn the panel to coldest A/C and fan (engine running) and try a couple of things to energize the clutch..... First, try jumpering the pressure switch plug with a paperclip.

I hope you are talking about the LP switch on the accumulator, not the pressure transducer on the HP line that sends the AC pressure to the PCM. Jumpering the 3-wire unit will only cause a code 67 and will not energize the clutch. As for the LP switch: ONLY try jumpering it if the static vapour pressure is equal to the expected pressure for the ambient air temperature (eg: if it's 70°F outside, the needle is about 70°F on the appropriate refrigerant scale.) The refrigerant circulates the lubricating oil to the compressor. Operating the compressor without refrigerant starves the compressor of oil and will quickly damage it.

Quote :

If this works, read the gauges and if the high is below 200 and the low is less than 10, you need to add freon.

Not necessarily. Refrigerant (trivia: Freon is a DuPont brand-name for R-12. R-134a is called "Suva") is a condesable, not a compressible. Provided there is one drop of liquid refrigerant in the system, the static pressure is a constant directly proportional to temperature. The dynamic pressures are a guide to what is going on in the system, not a guide to the charge in the system. It is entirely possible to have those pressures with a full charge, in which case you could impair or damage the compressor by adding more refrigerant.

Quote :

If the High is over 400, the switch was doing it's job by cutting off the electricity, and you should quickly pull the paperclip before something blows!

Again, I hope you are not talking about jumpering the transducer.

Quote :

For purposes of checking for low freon charge, you can run a jumper wire from pos batt post to the clutch wire and check your gauges. If they read 200-350 high (red gauge) and 14-50 on the low gauge (green) your problem is electrical. With these reading while the compressor is running, you should have cold A/C

You cannot tell the charge by the pressures. Pressures can tell you a lot about what is going on in the system, but not how full the system is. The correct way to determine the charge is to evacuate the system and weigh the refrigerant. Few shadetree mechanics have the appropriate equipment to do that. An alternative method is to estimate the charge based on the performance.

Liquid at the vapour point is the exact same temperature as vapour at the vapour point, although the vapour carries far more heat energy. In an ideal world, the liquid refrigerant entering the evaporator will have just vaporized as it leaves the evaporator. If it has fully vaporized before leaving the evaporator then the vapour can only cool by becoming superheated, which is inefficient compared to vaporization. If it has not fully vaporized then the refrigerant has not absorbed all the heat the evaporator should be able to, which again, is inefficient. So a guide to the proper charge is the difference in temperature between the inlet and the outlet -- the inlet shouldn't be any more than 3 or 4 degrees cooler than the outlet -- just the amount of liquid subcooling with no vapour superheating.

In reality, this will fluctuate, particularly in a CCOT (Cycling-Clutch/ Orifice Tube) system. The low pressure should cut off at 23 psi and cut back in around 40 psi, assuming the system can exceed the cooling demand. This translates to a temperature range of -4°C to 7° -- an average of just above the freezing point of water. It is not advisable to lower the pressure further or condensation will freeze on the evaporator and block air flow. On a hot humid day the system may not get down to the cut-out because the system cannot exceed the coolinng demand. Similarly, the system may not cycle at idle, but will cycle at higher rpm because the compressor can move more refrigerant around when it spins faster. Testing of the AC system is generally done at 1,500 to 2,000 rpm for that reason.

The high side can fluctuate wildly. "Normal" high side pressure could be anywhere between 150 and 400 psi, depending on the ambient air temperature and relative humidity. Humid air holds a lot more heat than dry air, and therefore the high side pressure will be much higher on a humid day than on a dry day for a given temperature.

If one keeps adding refrigerant to the system in an attempt to increase the pressure on a cool, dry day, one risks adding so much refrigerant that liquid not only exits the evaporator, it actually makes it as far as the compressor intake. Liquids don't like to be compressed, so this becomes a case of the immovable object encountering the irresistible force. Somethings gotta give and usually that something is inside the compressor. Conversely, if one assumes the refrigerant charge is adequate because the high side pressure is high on a hot or humid day, then one risks undercharging the system. An undercharged system starves the compressor of lubricating oil, which is merely a slower form of death.

I hope that the above is not seen as unfairly critical. Reading back, it could look a little aggressive. AC seems to be a poorly understood system and I just want to dispel some of the myths that often lead to heartbreak and tears. I learned much of the above the hard way.

I'm always willing to learn!.... I live in a place that is VERY hot and VERY dry, so what works for me doesn't necessarily work everywhere!
My point was to not start taking things apart before assessing if the clutch operates when putting 12 volts to it, and if it does, why the system is denying the 12 volts. As far as I know, the compressor must be running to get any gauge readings, and I was suggesting jumpering the compressor only to get readings, NOT to operate the system.

Whew,glad I am not the "one" that "buickwagon"keeps talking about because that guy is in big
trouble!

AzDon wrote:

My point was to not start taking things apart before assessing if the clutch operates when putting 12 volts to it, and if it does, why the system is denying the 12 volts.

An excellent approach to troubleshooting anything. Always check the simplest and easiest things first because a) they don't cost much time or money to check and b) they are usually the problem anyway. Even if it doesn't fix the problem, that approach often rules out a whole raft of other things.

However, in this particular case, he demonstrated that the clutch is getting power by giving it a tap. It's just that the gap is a hair too big. And that is a well known common issue that doesn't cost much time or money to check/fix.

I appreciate having knowlegeable folks around! I don't claim to know everything and am often the guy asking for advice and input.
The thread had looked to me as if the advice had moved towards disassembly before the electrical path to the compressor clutch had been given a clean bill of health. There are sensors that shut the compressor electricity down when they see an "out of parameter" situation. If the pressures in the system are right, those sensors SHOULD pass the electricity through to the clutch......That is why a leaking system usually will operate again simply by adding freon.
My strategy for troubleshooting is to have the system on at max/high fan and gauges hooked up when I start the vehicle and then jumper the clutch (if necessary)
If the gauges read low, I add freon and then try pulling the jumper wire to see if the system now runs without it (usually does)
If the pressures are right and the clutch jumpered okay, but it still won't run without the jumper, then I trace the system back to where the 12v stopped being passed through and replace that item after verifying it's lack of function by jumpering past it.
This is just general troubleshooting--I haven't consulted my OCC FSM yet to determine the exact A/C schematic, but I certainly will if I ever have these problems!
Repairing a factory system doesn't require an advanced degree in science or engineering because the engineering has already been done. We only need to understand the basic need for, and operation of each part and what happens when any of those parts fail.
Maybe I misread the thread and it had already been determined that 12v was present at the clutch, but it wouldn't operate. I replaced the clutch on a GM ASIX compressor once and it worked great till the compressor died a month later (for other reasons)
Now, I just replace a compressor that has these problems!
And YES! I agree that troubleshooting should start by checking the simple and cheap items first!

How difficult was it to replace the clutch? Did you have to evacuate the system?

I realize a compressor is easier in the long-long run, but I'm on a tight budget. lol



..not to just jump in on this AC thread or anything.

AzDon wrote:

We only need to understand the basic need for, and operation of each part and what happens when any of those parts fail.

Exactly. Most people don't understand the relationship between a refrigerant, it's temperature, and it's pressures. We are used to filling things by pressure -- tires for example. The tire is full when it has 30psi. It's initially hard to grasp the concept that one can keep putting refrigerant in the system without changing the pressure. Once one understands the basics, the rest starts to fall into place.

One thing that a lot of people don't think about when adding refrigerant is purging the gauge and charge hoses to remove all air. Air in the system impairs the efficiency. That's one reason why the system should be under a deep vacuum before charging. The vacuum also removes moisture by lowering the boiling point of any water in there.

Stingroo wrote:

How difficult was it to replace the clutch? Did you have to evacuate the system?

I realize a compressor is easier in the long-long run, but I'm on a tight budget. lol

The system does not have to be evacuated to replace just the clutch (it does if you have to replace the bearing or seal behind the clutch). However, it's rare that a clutch needs replacing before the compressor. What are your symptoms?

Quote :

..not to just jump in on this AC thread or anything.

Come on in, the water's fine.

pretty cool topic,.

buickwagon wrote:

Stingroo wrote:

How difficult was it to replace the clutch? Did you have to evacuate the system?

I realize a compressor is easier in the long-long run, but I'm on a tight budget. lol

The system does not have to be evacuated to replace just the clutch (it does if you have to replace the bearing or seal behind the clutch). However, it's rare that a clutch needs replacing before the compressor. What are your symptoms?

Quote :

..not to just jump in on this AC thread or anything.

Come on in, the water's fine.

I can hear it making this hellacious clicking and clacking noise, but only when the AC is on.

Probably bearings then, no?

Ugh.

Okay.... I consulted my OCC FSM regarding electrical path..... These wagons use a cycling switch on the low side screwed to the side of the accumulator that disconnects power below 23psi and above 43psi as read on a low side (green) gauge (the gauge on the left)
The electricity goes from the panel thru the cycling switch thru the relay and then to the compressor. The relay is next to the fuel pump relay adjacent to the accumulator tank and passes the power thru unless the realay is energized by the computer (ECM) providing a ground to the relay's electromagnet which disconnects the compressor's power path.
There is no high-side pressure protection switch on these cars, but know that high-side pressures above 400psi can lockup the compressor and burn the belt off (not cool) so it's still a relevant pressure to know
I'm thinking that the clutch engaged when he touched it either by coincidence, or because he touched the wire plug and maybe it was loose or not making proper contact.

Replacing a compressor clutch requires some specific puller and press-on tools and is fairly easy. My clutch had come apart, but most are screwed up because the compressor has problems, so I've never needed to replace a clutch since.

AzDon wrote:

There is no high-side pressure protection switch on these cars, but know that high-side pressures above 400psi can lockup the compressor and burn the belt off (not cool) so it's still a relevant pressure to know

That's a difference between the RMW and the OCC then. The RMW has a pressure transducer to tell the PCM what the high-side pressure is. The PCM will kill the compressor if pressure exceeds 430psi or drops below 0psi. Also at WOT, high power steering pressure and as the engine coolant begins to overheat.

[quote]I'm thinking that the clutch engaged when he touched it either by coincidence, or because he touched the wire plug and maybe it was loose or not making proper contact.[\quote]

Coincidences are rare, but possible. However, he said he tapped the clutch. 99.9% of the time, if that causes the clutch to engage, the problem is an excessive clutch gap. The electromagnetic coil just isn't strong enough to bridge the gap but easily holds the clutch in if tapped. Or sometimes even going uphill is enough to engage it.

Stingroo wrote:

I can hear it making this hellacious clicking and clacking noise, but only when the AC is on.

Probably bearings then, no?

Ugh.

Look carefully at the center of the compressor hub. Is it turning constantly, or starting/stopping with the noise?

Also, have a look at the idler pulley. Is it swinging wildly, trying to take up tension as the belt stretches dramatically?

Belt tension is good, that much I can confirm. I've changed everything on the front end of the motor other than the crank pulley and AC in the last month or so.

Yeah, I'm not saying the tension is the problem. But if the compressor is hammering (eg: being liquid slugged from over-charging) then the shock on the belt with the AC on may be making the tensioner go nuts.

Hi all, great thread here. I was digging through it today after the ac on the RMW died this afternoon. Ironically, exactly the same symptoms as the original post.

At any rate, full of charge, no blown fuses ... And the hammer on the ac clutch worked. Running nice and cold again for now (much to the wife's happiness - she loves the ac on the Buick, best in the fleet).

Looks like the consensus is get a new (non rebuild) unit? I'd rather not do this again in the near future.

So the compressor is fine -- you just need to adjust the clutch gap. Can be done with the compressor in place. You just need the tool, and can borrow that at some parts stores.

Good point, I was thinking the clutch was just starting to fail in general but I guess that's not necessarily true.

Even if the clutch is shot, you can replace just the clutch without removing the compressor. It's a crapshoot from there as the compressor may fail in the future of course, but if it's working at the moment and has never been improperly serviced, has adequate oil in the system, etc. it may last for years.