AC problems 2002 Cavalier

Given the numerous dandy observations and symptoms, I'd start with a load test on the generator. To start with, GM went from the world's second best AC generator to the worst pile ever beginning with the 1987 model year. You already found one of the main problems with the defective voltage regulator. In addition, it is real common for them to develop bad diodes. When one out of the six fails, you lose two thirds of the output capacity. That leaves you with 25-35 amps which is not enough to meet the demands all the time.

The fix for these repeat failures is to replace the perfectly good battery. Due to their design, these generators develop huge voltage spikes that destroy the voltage regulator, diodes, and "induce" voltage spikes into adjacent wires. If those wires are for a computer sensor, the computer will get confused and do weird things.

As the battery ages, it loses its ability to dampen and absorb those voltage spikes. It is real common to go through four to six generators in the life of a GM vehicle but replacing the battery at the same time, unless it's less than about two years old, will reduce the number of repeat failures.

During the load test, also watch the "ripple" if the tester displays it. It is not a value; it is just a relative bar graph. If ripple is high and maximum output current that can be obtained is near one third of the normal 90 or more amps, suspect a defective diode.

Codes do not need to be checked when the Check Engine light is on. When the light turns on in a Chrysler product, there WILL be a code in memory. Things are different with GM cars. On GMs, the light often turns on when the computer is watching something it isn't happy with but it hasn't met the criteria to set a code yet. They call that a "pending" code. When you check for stored codes, you have to also check for pending codes. I don't know if the simple code readers used by many auto parts stores will do that. Typically they can retrieve hard codes. Hard codes remain in memory and can be read even if the Check Engine light goes off.

The next approach is to connect a scanner that displays live data and watch what's happening on a test drive. Even with a dead AC condenser fan or radiator fan, the AC should work fine at highway speed due to the natural air flow. The AC won't stop working because the fan motor is bad. It will stop working because DUE to the dead fan, the high-side pressure gets too high and a safety cutout turns the compressor off. I'm not enough of an AC expert to say what your system is doing without having pressure gauges attached, but that rapid cycling that you correctly associated with low refrigerant charge could also be occurring from too much pressure.

Something else to keep in mind, although I don't think it applies here, is if the system isn't regulating properly, the evaporator in the dash can get too cold resulting in cool or even warm air. The system regulates at near 40 pounds of pressure which just happens to equate to close to 40 degrees. The air coming out of the ducts is only supposed to be 20 degrees colder than outside air but the real comfort comes from removing the humidity. That moisture should be draining onto the ground and leaving a puddle under the area of the front passenger's feet. If the evaporator gets too cold, that water will freeze solid and block air flow. That's when the duct air temperature goes up. You can identify that by checking for that normal drainage under the car as soon as it starts blowing warm air. If there's very little dripping water, watch what happens after the engine has been off a couple of hours. If you get a really big puddle hours later, the evaporator is freezing up.

Another thing to consider is there is no way to know how much refrigerant is in the system unless you completely drain it, pump it into a vacuum for at least half an hour, then refill it with a measured amount. Part of the system has liquid and part is vapor. When the system has been off a while and the high and low sides have equalized, the pressure will be very near the outside temperature. If you bleed off a bunch of pressure in the form of a vapor, some of the remaining liquid will just vaporize and expand a bunch and the pressure will go right back up to where it was. No matter how much you bleed off, (or leaks out), the pressure will remain the same until so much is gone that ALL the liquid has vaporized. Then you will have the same thing as a tire, ... All vapor, and the pressure will drop as you bleed some off.

For that reason, there's no way to know how much refrigerant to add unless you start from "empty". It's also real easy to overcharge the system. The refrigerant turns real cold at the point where it expands from a liquid to a vapor. You want that to be in the middle of the evaporator, but if there's too much in the system, after it's running a while, that evaporation might take place after it leaves the dash and heads back to the compressor. You can identify that by ice buildup on the hose going to the compressor. Wetness is normal, but ice is not. Even with a pair of gauges attached, system pressures will appear normal with a partial loss of charge or with some overcharge. The only thing you can assume is if the compressor begins cycling rapidly on and off after it has been working fine for months or years, is it's not due to an overcharge since refrigerant only leaks out, not in.

Beginning in the early '90s, Chrysler started using some AC compressors that run continuously and don't cycle on and off, and I'm betting GM went to a similar design. The pressure in the system pushes on the "wobble plate" and adjusts how much volume it tries to compress. Instead of switching between fully-on and fully-off, it self-adjusts as needed. In those systems, cycling on and off is a new clue to an undercharge or overcharge.

Given the age of the car too, look around under the hood for signs of leakage. Oil circulates with the refrigerant and will leave evidence of that leakage. Look in particular where rubber hoses are crimped to metal pipes. If you see wetness there, suspect the system is simply low on charge again. Dye can be added to the refrigerant, then if the problem occurs again days or weeks later, you search with a black light. The dye will show up as a bright yellow stain.

God Doc, I don't know why you hate GM so much. Most of what you point out as faults isn't even true. I personally think Chrysler is the most ass backwards design out there. Who else would do a foolish thing like make the voltage regulator part of the PCM? You don't see belts flying off GM engines all the time either.

Original poster, you seem to be checking everything except the one thing that you should have started with. You can't have any idea at all what is going on in an A/C system without putting gauges on it and knowing exactly what the (high and low) pressures are both at idle and at 2000RPM. You have a CCOT (cycling system) that uses an orifice tube. The full time system Doc referred to is only used with an expansion valve system. Get the pressures read while the problem is present and we'll try to analyze them for you.

What's got your dander up this time? Putting the voltage regulator inside the PCM would never be my first idea but they do give very little trouble. Also, they can kill the field current when a few more horsepower is needed such as at wide-open-throttle.

GM has always been the company famous for building assemblies that require people to buy much more than needed. Look at the HEI ignition system. A real nice ignition system but it was meant to be a unit replacement when it was new since a lot of mechanics didn't know how to work on them at first. ABS wheel speed sensors built into wheel bearings so you have to buy a complete assembly. You're going to spend way more on wheel bearings than I'm going to spend on PCMs. Who has more trouble with false ABS activation at low speed than GM?

Same with GM generators. Everything built in so you get to buy way more than you need. Why did they go to a design that has to just about be destroyed to even get to the voltage regulator, and there's no way to full-field it to test it. The old SI systems used a switch-mode voltage regulator that turned on and off 400 times per second. Turning off the current to any coil of wire sets up a voltage pulse just like in an ignition coil. Why did they never have a problem with them taking out the diodes or voltage regulator? The new CS design switches the same way but suddenly they have all kinds of trouble. Chrysler switches theirs the same way. They don't have trouble. Same with Ford. No trouble with diodes and regulators. Only GM has had this problem since they brought this design out. They even use zener diodes to help short out those voltage spikes but that doesn't completely solve the problem. When is the last time you heard of an engine running better when the generator was disabled? It was on a GM. Don't you think at some point they would design a solution to this very common problem? They've had 25 years, yet they still have the same problem. Ryan is on his third regulator or generator in six months, and this all too common. I have a friend with a '96 Buick that went through four generators in two years. The problems stopped after her battery went bad and was replaced. Another friend has a '99 GMC Suburban. I helped him put in his third, (second replacement) generator two months ago.

As for the new battery solving most of the trouble, I didn't figure that out myself. That comes from a GM corporate trainer through a Carquest trainer who puts on very high-level classes. He has a business near Chicago that specializes in that one out of a hundred cars that no other shop can diagnose. His customers are mainly other shops. He has a network of other trainers all over the country including people from every manufacturer. In fact, he drives a Buick.

At every class he starts with how a system works on one brand of car, then on the second night he goes into the odd problems and how they solved them. He doesn't waste any time on the "common" stuff. He rarely has a Chrysler-specific class because they don't have that many hard-to-diagnose problems that pertain only to that brand. Their hard-to-diagnose problems are similar to what could be found in any other car brand. That doesn't mean they're better or worse.

Same with GM. They aren't better or worse, but they sure do like to make changes. I noticed that first when a friend had a stash of oil filters for his Camaro, but when he traded it for a Firebird, the filters were different. If one was better, why didn't they use it on both cars? PCV valves are even worse. All through the '70s and '80s, Chrysler had two, GM had how many dozen? We never had the right one in stock.

I can give you a HUGE list of things I do not like about Chrysler, but business practices doesn't make that list. I don't like the regulator in the PCM, but who has the alternator that can have the brushes replaced often without removing it from the engine? The most common failure is a nine-dollar brush assembly at around 150,000 miles. By that mileage, how many GM cars still have their original AC generator yet? (Notice I didn't call it an alternator. Chrysler copyrighted that term in the '60s so now we call them "AC generators").

Getting back to air conditioning systems, I said I wasn't the expert, but the system I was referring to regulates with a variable displacement compressor. The offset of the wobble plate is adjusted by the low side pressure coming out of the evaporator. I know similar systems are used on other cars so I merely surmised GM was likely using something similar too, and if so, normal operation is the compressor clutch stays constantly engaged. If that is normal operation, then it cycling on and off would be due to low charge. I know there's a good chance I'm wrong, as we all know you love to point out, but at least I've suggested a few more things to consider and look for.

You're right about needing gauges but that isn't going to tell the whole story. There's no way to know how much refrigerant was in the system before more was added, so we don't know if the system is overcharged or if there's a leak and it's undercharged. All we can do is go by the observation that the system appeared to work okay for a while after refrigerant was added. What's the first thing YOU would do if you were asked to diagnose this car? You'd open the hood and look at it. Can't do that here. What else? You'd listen to it. Can't do that either. All you got is the information given and from those observations ten people are going to suggest ten different things.

The additional clue is the AC problem seems to have been fixed by fixing the generator, ... Twice. So do we infer that the third time for the same symptom is caused by the same defect? If not, it would be quite the coincidence to solve a problem twice with the same remedy but not the third time. Coincindenses do happen, but you have to consider GM's track record for generator problems. When you have such a common problem staring you in the face, it's silly to go looking elsewhere for the less-likely causes first. To say it can't be the generator because it's new doesn't cut in this case. Once it is ruled out, THEN you have to consider that there's an AC problem that has nothing to do with the charging system, and given the symptoms and previous repairs, a leak in the system is a real good possibility regardless of what type of system is used on that car.

Apparently, you like typing a lot more than I like reading so I'm not even going to attempt to respond. I just wonder why you like to use this forum to attack GM. Nobody else seems to concur with you on that subject.

A couple of things come to mind. First of all, run it in gear with a helper holding the brakes on, (unless you trust your parking brake), and watch if the compressor is still running when the AC gets warm. If it is not, I would look first for a wiring harness that is flexing when the engine rocks. If the compressor disengages, put it back in park, then wiggle the harnesses to the compressor clutch, low-pressure cutout switch, and anything else related. Stretched connector pins can be tightened. Corroded terminals should be replaced. Look for wires that are rubbing on sharp metal brackets.

The Check Engine light is telling you there's a diagnostic fault code stored in the Engine Computer. Many auto parts stores will read them for you for free. You might as well start with that since it could be a clue to this problem.

The next clue is how long does it take to stop working. If it continues to blow cold air for a minute or two after you start driving, then the air gradually gets warmer, air volume seems to go down, and the compressor is still running, you might suspect the evaporator in the dash is freezing up. The low side pressure is regulated so the temperature never gets below about 40 degrees. If it gets below 32 degrees, condensation from removing the humidity will freeze into a block of ice instead of dripping onto the ground and will block air flow. Besides the lack of a puddle on the ground where you stop, another clue is it will have to sit a long time for that ice to melt before you'll get cold air flow again. If you can get cold air right after shifting to park, ice is likely not the cause. Ice buildup is due to the system not regulating properly, and the first place I'd look is at that temperature sensor. Systems with an expansion valve have a sealed bulb filled with gas that is inserted in the fins of the evaporator in the dash. The system won't regulate properly if that bulb isn't inserted fully in the right spot. Your system regulates differently. If ice buildup seems to be the problem, we'll have to get Wrenchtech involved. The potential clue is the system seems to work at night when the humidity might be lower and ice blockage would be less of a problem.

The things the guys mentioned about idle speed do not seem like they're related to the compressor turning off. I suspect you're not going to find a common, or "pattern" failure. To me this sounds like something was wired incorrectly during a previous repair, or there is some other wiring harness issue. The simple fact that the compressor runs and the system cools properly at times says there is not a component failure. It's a switch / wiring / connector-type of problem or it's related to the amount of refrigerant in the system.

Be aware there is a recurring problem with this site where it sends us to the wrong post after we post a reply. This has happened before and they usually correct it within a few days. Don't think we're ignoring you if we don't get back to you right away.