Quantcast
Jump to content

Pulsing Voltage To A/C Compressor, 02 VW Jetta


Recommended Posts

A 2002 VW Jetta arrived at our shop the other day, the customer complaint…no air conditioning. The system was fully charged so we started our diagnostic tests and found that there was a pulsing voltage to the a/c clutch. The fan control module would pulse a 12 volt signal every few seconds.

 

After a little research we learned that a faulty compressor clutch could be the fault. We ohmed the clutch coil and found it open. We replaced the compressor clutch and now the FCM sends a constant 12 volt signal and all is ok.

 

Maybe others have seen this, but it stumped me and my lead tech at first. Apparently, if there is a problem with the clutch coil, the voltage will pulse from the FCM.

 

It's a good thing we did a little research to find how the system works before shot-gunning the problem.

 

 

I've run across that one before, but, I have one problem I've found with the newer beetles that will throw you a curve ball... If you get a Beetle with A/C problems... do this little test first.

With the car idling and A/C on... and you get no cold air... BUT... if you bring the engine rpms up to say... 2 grand or so ... if now you have perfect cold air the problem is not the A/C ... it's the charging system. The feedback current from the alternator is too low at idle for the PCM to recognize that the charging system is working. However, it is high enough to keep the charge light off. The PCM reacts by assuming the charging system is shot and starts shutting down accy systems to avoid overloading itself.

To make matters worse... everytime I ran across this problem I have never been able to see a voltage change at the battery with a meter. But, believe me... it's the alternator. The last one I did was probably the worst one. Everything looked great, but I changed the alternator anyway. As soon as I did... the A/C kicked on... blowing cold air just like you would expect.

Hope this helps... Gonzo

Edited by Gonzo
Link to comment
Share on other sites

That's a great tip, Gonzo. Maybe we should post more of our technical war stories. Afterall, if we can help each other to become more profitable in the shop, it helps our business.

 

let's do...

Link to comment
Share on other sites

  • 8 months later...

I've run across that one before, but, I have one problem I've found with the newer beetles that will throw you a curve ball... If you get a Beetle with A/C problems... do this little test first.

With the car idling and A/C on... and you get no cold air... BUT... if you bring the engine rpms up to say... 2 grand or so ... if now you have perfect cold air the problem is not the A/C ... it's the charging system. The feedback current from the alternator is too low at idle for the PCM to recognize that the charging system is working. However, it is high enough to keep the charge light off. The PCM reacts by assuming the charging system is shot and starts shutting down accy systems to avoid overloading itself.

To make matters worse... everytime I ran across this problem I have never been able to see a voltage change at the battery with a meter. But, believe me... it's the alternator. The last one I did was probably the worst one. Everything looked great, but I changed the alternator anyway. As soon as I did... the A/C kicked on... blowing cold air just like you would expect.

Hope this helps... Gonzo

 

On these cars check voltage output in ECU measuring blocks. I've seen a number of odd problems caused by voltage issues on VW/Audi cars and Benz's. A new regulator solves the problem. I often have it on the top of my list to check voltage and alternator output and ripple when diagnosing drive-ability or anything that stumps me at first. I do forget sometimes. Had a Chrysler in here the other day with erratic idle and instrument cluster quirks, luckily stumbled on the negative terminal being loose, a quick clean and tighten solved all the problems.

 

Haven't stumbled upon this A/C problem yet but its that time of year now so I'll keep it in mind.

Link to comment
Share on other sites

A 2002 VW Jetta arrived at our shop the other day, the customer complaint…no air conditioning. The system was fully charged so we started our diagnostic tests and found that there was a pulsing voltage to the a/c clutch. The fan control module would pulse a 12 volt signal every few seconds.

 

After a little research we learned that a faulty compressor clutch could be the fault. We ohmed the clutch coil and found it open. We replaced the compressor clutch and now the FCM sends a constant 12 volt signal and all is ok.

 

Maybe others have seen this, but it stumped me and my lead tech at first. Apparently, if there is a problem with the clutch coil, the voltage will pulse from the FCM.

 

It’s a good thing we did a little research to find how the system works before shot-gunning the problem.

 

 

Sounds they are using a current detecting transistor in the output from the module, either that or they are monitoring the feedback diode for current load and if the system sees a out of spec condition it will refuse to power the circut.

 

I'd have to check the diagram but this AC clutch was not relay drive ?

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Have you checked out Joe's Latest Blog?

         4 comments
      I recently spoke with a friend of mine who owns a large general repair shop in the Midwest. His father founded the business in 1975. He was telling me that although he’s busy, he’s also very frustrated. When I probed him more about his frustrations, he said that it’s hard to find qualified technicians. My friend employs four technicians and is looking to hire two more. I then asked him, “How long does a technician last working for you.” He looked puzzled and replied, “I never really thought about that, but I can tell that except for one tech, most technicians don’t last working for me longer than a few years.”
      Judging from personal experience as a shop owner and from what I know about the auto repair industry, I can tell you that other than a few exceptions, the turnover rate for technicians in our industry is too high. This makes me think, do we have a technician shortage or a retention problem? Have we done the best we can over the decades to provide great pay plans, benefits packages, great work environments, and the right culture to ensure that the techs we have stay with us?
      Finding and hiring qualified automotive technicians is not a new phenomenon. This problem has been around for as long as I can remember. While we do need to attract people to our industry and provide the necessary training and mentorship, we also need to focus on retention. Having a revolving door and needing to hire techs every few years or so costs your company money. Big money! And that revolving door may be a sign of an even bigger issue: poor leadership, and poor employee management skills.
      Here’s one more thing to consider, for the most part, technicians don’t leave one job to start a new career, they leave one shop as a technician to become a technician at another shop. The reasons why they leave can be debated, but there is one fact that we cannot deny, people don’t quit the company they work for, they usually leave because of the boss or manager they work for.
      Put yourselves in the shoes of your employees. Do you have a workplace that communicates, “We appreciate you and want you to stay!”
  • Similar Topics

    • By Changing The Industry
      Enhancing Shop Operations with John Heller of PartsTech
    • By Changing The Industry
      The Basics of Owning An Auto Repair Shop - Part 5
    • By carmcapriotto
      The Weekly Blitz is brought to you by our friends over at Shop Marketing Pros. If you want to take your shop to the next level, you need great marketing. Shop Marketing Pros does top-tier marketing for top-tier shops.
      Click here to learn more about Top Tier Marketing by Shop Marketing Pros and schedule a demo:https://shopmarketingpros.com/chris/
      Check out their podcast here: https://autorepairmarketing.captivate.fm/
      If you would like to join their private Facebook group go here: https://www.facebook.com/groups/autorepairmarketingmastermind
      In this episode, Chris Cotton from Auto Fix Auto Shop Coaching explores the issue of transition leaks in auto repair shops. He explains how frequent task-switching hampers productivity and energy levels for shop owners, service advisors, and technicians. Chris advocates for batch processing to consolidate similar tasks, thereby reducing transition leaks and increasing efficiency. He advises reorganizing work schedules to minimize cognitive load and suggests that while flexibility is necessary, intentional planning can greatly enhance productivity. The episode wraps up with Chris encouraging listeners to embrace growth and efficiency, thanking the sponsor, and promoting a positive work ethic.
       
      Transition Leaks (00:00:06) Explanation of the concept and its impact on auto repair shop owners, service advisors, and technicians.
       
      Impact on Efficiency (00:02:27) Discussion on how transition leaks lead to lost efficiency and diminished capacity for delivering high-quality service.
       
      Batch Processing Strategy (00:04:48) Explanation of the batch processing strategy to combat transition leaks and improve productivity.
       
      Applying the Concept (00:07:03) Guidance on analyzing and reorganizing schedules to minimize transition leaks and increase efficiency.
       
      Embracing Change (00:09:11) Encouragement to prioritize efficiency and quality by embracing a new way of organizing work schedules.
       
      Connect with Chris:
       
      [email protected]
      Phone: 940.400.1008
      www.autoshopcoaching.com
      Facebook: https://www.facebook.com/
      AutoFixAutoShopCoachingYoutube: https://bit.ly/3ClX0ae
       
      #autofixautoshopcoaching #autofixbeautofixing #autoshopprofits #autoshopprofit #autoshopprofitsfirst #autoshopleadership #autoshopmanagement #autorepairshopcoaching #autorepairshopconsulting #autorepairshoptraining #autorepairshop #autorepair #serviceadvisor #serviceadvisorefficiency #autorepairshopmarketing #theweeklyblitz #autofix #shopmarketingpros
      Click to go to the Podcast on Remarkable Results Radio
    • By Joe Marconi

      Premium Member Content 

      This content is hidden to guests, one of the benefits of a paid membership. Please login or register to view this content.

    • By carmcapriotto
      Matt Fanslow explores the analogy between running a repair shop and the world of dating. He shares insights on first impressions, trust-building, and the value of substance over style in both customer relationships and shop management. Matt emphasizes the need for repair shops to maintain high standards of service and to view customer feedback as opportunities for growth.
      Show Notes
      Dating in Modern Times (00:01:15) Comparison of modern dating to historical dating and personal experiences with initial interactions. Physical Attractiveness and Shop Appearance (00:02:25) Reflections on interactions with physically attractive individuals, similar to the importance of a shop's appearance. Importance of Customer Reviews (00:04:54) Discussion on the significance of customer reviews, the impact of negative reviews, and the importance of backing up a shop's exterior with quality service. NAPA Auto Tech Training Sponsorship (00:11:34) Information about NAPA Auto Tech Training and its benefits for technicians and shop profitability. Constant Improvement in Customer and Employee Interactions (00:13:42) Emphasis on the importance of constant improvement in customer interactions and the parallels with employee relationships. Long-Term Relationships and Continued Accreditation (00:17:06) Discussion on the importance of continued accreditation and constant improvement to maintain long-term relationships with customers and employees. Shop Relationship Parallels (00:18:13) Drawing parallels between shop hiring and dating, emphasizing the importance of attracting and maintaining long-term relationships with employees. Attracting Talent (00:19:16) Encouraging self-reflection on what attracts and separates a shop from competitors, and the importance of perpetuating long-term relationships with employees. Promoting Training (00:20:20) Advocating for the importance of training.  
      Thanks to our Partner, NAPA Autotech napaautotech.com
       
      Email Matt: [email protected]
      Diagnosing the Aftermarket A - Z YouTube Channel HERE
      Aftermarket Radio Network: https://aftermarketradionetwork.com/
       
      Click to go to the Podcast on Remarkable Results Radio


  • Our Sponsors

×
×
  • Create New...