Automotive Air Conditioning Information Forum (Archives)

dsorg on Wed June 27, 2012 11:48 AM

Year: 2002
Make: Dodge
Model: Grand Caravan
Engine Size: 3.3 L
Country of Origin: United States

My 2002 Dodge Grand Caravan AC compressor failed at about 120,000 miles by seizing up. I drove it 2 more months before taking it to the shop for analysis. I was told that the cooling fans weren't turning on and that the compressor likely failed due to lack of cooling fan operation. I was warned not to drive the car until I replaced the ECM computer. They had applied power to the fan control module and the fans ran but claimed that the fans wouldn't come on as the engine temperature went up so the computer was the only other thing that could be at fault. They think there is an intermittent failure in the output of the computer to the fan control module. This was hard to believe since I'd been driving the car in hot weather in all driving conditions and had no apparent overheating problems. Furthermore, upon leaving the shop without making repairs, I observed the fan operation for the next 2 months and found no problems with the overheating.

So I ended up having the repair shop replace the compressor and charge the system and then took the car to the dealer to potentially have the computer replaced. They said the computer was working fine and the fans operated normally. I made the assumption that the first repair shop guys simply didn't understand the conditions under which the fan should run and I took the car home. I had no problems with the AC or the engine temperature for almost a year. Then I flipped the defroster on one cold morning and the compressor seized up again, smoking the belts briefly before breaking the compressor internally and allowing the shaft to turn again. I returned back to the repair shop and was once again told that the fans weren't coming on. They eventually replaced the compressor but left the clutch disconnected pending my promise to replace the computer, after which they promised they would charge the system for me.

So here I am, several months later. I have not replace the computer but was considering doing so in order to get the shop to charge the AC system. The problem is that I don't think the computer is at fault. I'm betting on a bad pressure switch. I'm not an AC professional but did some online research and see that there are multiple inputs to the computer that determine when the fans run. My unprofessional theory is that the pressure transducer (switch) is intermittently failing so that the compressor sometimes builds excessive pressure due to lack of cooling. I'm prepared to eat crow on this but I need to make a decision on what to replace to fix this problem. I'm thinking that most of the time, the engine or transmission or some other control requirement makes the fan run so the AC system usually stays cool enough to survive, even though the pressure switch wasn't supplying the correct signal to the computer to call for fan operation. Maybe there were some times when the AC system didn't get cooled properly and the compressor took a beating but didn't immediately fail. There was evidence that the pressure relief valve had opened.

So I am on a quest for understanding about how this system works so I can argue with the mechanic against changing the computer. I have a brand new compressor on the car but the system is not charged and the shop won't complete the job until I replace the computer. Can someone explain for my car, under what conditions is the fan supposed to run? The pressure switch is a 3 wire switch. I've seen references to the pressure needing to reach a minimum level for the clutch to kick in and another pressure level again for the fan to run once the pressure builds a bit. I don't know if the pressure switch also operates as a high pressure switch to shut power off to the clutch. I just need to understand how this works so I can talk intelligently to the guys at the shop. I'm open to any other help to understand what is really happening here too.

Thanks!

Dave S.

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Dave S

GM Tech on Wed June 27, 2012 12:17 PM

If they told you the left rear tire needed replaced to fix the a/c, would you do that as well? You are too gullable- find an a/c shop!! Pronto.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

dsorg on Wed June 27, 2012 1:22 PM

I'd have to disagree with you on being gullible. I didn't buy the bad computer theory and didn't replace it because I reasoned that it wasn't the correct answer. How is that gullible?

I took the rational step to write to this forum to gather more information before making a decision. I like to understand what's going on when I take a car in and I don't buy off on any explanation I get if it doesn't add up.

FYI - this shop has always done right by me in other repairs. They also do a fair amount of AC work so I didn't think it was unreasonable to have them replace the first compressor. They didn't charge me for any parts or labor when they put the 2nd compressor on so they are not milking me for money. They don't want to sell me a computer either as they don't want to deal with the flash programming issues.

I think they just are looking at this situation backwards. I don't think the problem is in the output of the computer, I think it's in a bad input signal.

It would be great to hear back from you if you have any constructive comments. I can do without the insults.

Thanks!

Dave

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Dave S

GM Tech on Wed June 27, 2012 4:01 PM

If you like your shop- then use them- let them reasearch your issue and let them fix it----

would you second guess your doctor? A good doctor researches the issues for you.. Likewise a good shop researches the proper fix for you-- so that you don't have to--- Just find a shop that will do the necessary research for you.....simple as that.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

NickD on Wed June 27, 2012 6:32 PM

R-134a, PAG oil that absorbs moisture like crazy, and now, two seized compressors, then leaving the system uncharged where even more moisture can get in. Absolutely against all the known rules about R-134a AC repair. And what about the original accumulator and condenser. Almost next to impossible to flush out a parallel flow condenser, add these two important items to your throwaway list.


Rest of the system needs to be flushed, deep vacuum drawn after all repairs are made, then the correct amount of PAG injected, then charged. I didn't make these rules or procedures.

Can't really help you on fan control without a circuit diagram and explanation. Big deal lately with playing with the fan for supposingly better fuel economy. Wait until the system whether AC or cooling is about ready to blow up before kicking it on. That's all they have left to play with, EPA is already insisting on adding nitrogen, oxygen, ethanol, MBTE's to our fuel we are paying four bucks a gallon for, and BTU ratings have dropped as much as 30%. More like paying $5.60 per gallon of fuel, rest is free air they are charging us for.

So what do they do to help improve fuel economy by 0.00001%? Play with the fan.

Regarding your real problems, sure sounds like your vehicle was not repaired correctly. I don't know, wasn't there, just read your frustrated post.

Edited: Wed June 27, 2012 at 6:34 PM by NickD

dsorg on Wed June 27, 2012 7:03 PM

It's possible that something wasn't fixed right and caused the 2nd compressor failure but I know that the accumulator and dryer were replaced, the system evacuated and new oil put in on the first repair. I'm not sure if the system was evacuated when the 2nd compressor was put on or even if they put the oil in yet, but the hoses are hooked up and everything is sealed so I don't see more moisture getting in.

I think that as you pointed out, the manufacturers are doing so many wierd things in an attempt to save gas that common logic no longer applies to control systems. That's why I think it's distinctly possible that the shop is missing something when they tell me the fan isn't coming on when they think it should.





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Dave S

NickD on Wed June 27, 2012 8:15 PM

So what's the story on the condenser? When a compressor gets old and fatigued, bits and pieces break off and are blown into the condenser, and other bits and pieces will eventually seize and lock up the old compressor.

Was possible to flush out the old R-12 tube and fin type, but R-134a requires a parallel flow condenser, impossible to clean. But no better cleaner than a real high pressure R-134a flush that gets that debris recirculated into the new compressor, so the new compressor will seize as well.

Should have been replaced.

dsorg on Thu June 28, 2012 1:33 PM

Interesting point.

I'm sure the condensor wasn't replaced. I'm not an AC guy so I wouldn't have known that you couldn't properly flush a newer condensor.

Another point I forgot about is that this car has rear AC so the shop told me that it would increased the possibility that something could be left in the lines. Maybe there never was anything wrong with the fan and the shop just didn't get the lines clean, despite their best efforts. They did tell me that they inspected the lines as best they could and didn't see any contamination but of course they could only see the first inch or two of the lines and that doesn't tell you much.

I think I'm just going to pay someone to charge the system, check the output from the pressure sensor and hope for the best. If it fails again, I'm done.

Thanks for your input.



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Dave S

HECAT on Thu June 28, 2012 3:43 PM

Quote
Originally posted by: NickD
parallel flow condenser, impossible to clean.

I disagree

But you already new that.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

NickD on Thu June 28, 2012 5:34 PM

Quote
Originally posted by: HECAT
Quote
Originally posted by: NickD
parallel flow condenser, impossible to clean.



I disagree



But you already new that.

Okay, so progress was made in this condenser area, but from the sounds of his post, nothing was cleaned. In some manuals, they recommend adding a filter at the output of the condenser.

Do your agree that if he goes someplace else to have it charge, his new compressor will fail as well without at least having the entire system cleaned first?

jglanham on Thu June 28, 2012 6:23 PM

dsorg:
What you are calling a pressure switch is actually a pressure transducer. It is an electronic circuit that constantly monitors the pressure. It sends signals to the Powertrain Control Module. (same Module that controls the fans) The transducer can fail in which case the clutch circuit opens up. It can also become intermittent, which causes the clutch to randomly drop out.
Have you checked for error codes? The MIL (malfunction indicator lamp or check engine lamp) will
not come on for many error codes.
The engine coolant temperature sensor feeds a signal to the PCM, which controls fan operation. You need to see if codes have been set for fan circuit failures. If no codes have been set, chances are the fans have not failed. You can check if the fans run by placing a sheet of cardboard in front of the radiator to block airflow. Just don't let the engine overheat. However, compressor failure is unlikely to occur due to fan failure, since the high side pressure will rise rapidly and the sensor will disengage the clutch until the pressure drops to a safe level.
I agree that it sounds like there is debris in your system if you keep seizing up compressors.
The two main causes of compressor seizures are lack of lubrication or debris in the system. If the system was not flushed after each compressor failure, chances are that you do have debris in your system. If you don't flush, your new compressor will fail, guaranteed! Sometimes it is cheaper and more reliable to replace the condenser, just depending who does it and how they do it.
Just a comment about the PCM: They rarely fail. Your dealer has the factory instruments to determine its functionality. You indicated that they told you it is fine. Believe them, as they would love to sell you a new one if it wasn't!!
Since you haven't indicated that the shop that replaced the compressors, flushed the system, I would look for another shop to do the work. They obviously are not familiar with the correct way to repair an a/c system. Read the info on this website about the correct methods for servicing a/c. They have been written by professional a/c technicians with many years of experience.

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johnl

dsorg on Wed July 25, 2012 3:59 PM

Thanks to all. I am going to take it to a better qualified AC shop and see what they can do for me.

Dave

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Dave S

JJM on Sat July 28, 2012 4:54 PM

Repeat failures are typically the result of poor quality parts (rebuilt or remanufactured compressors), and improper (or nonexistent) flushing techniques.

Even if the fans weren't coming on, whatever HPCO (required by EPA rules) method is used, it should cut the compressor off. A compressor typically does not seize up from high pressure, but there are plenty of ways to test this - one of which is a simple piece of cardboard over the condenser.

Any decent scan tool should be able to check A/C status and fan operation.

Joe

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