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post #1 of 16 (permalink) Old 06-25-2019, 07:13 PM Thread Starter
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A/C Issues

hi all,

I have a 2001 C320, My A/C works intermittently. For example, when the engine is running and going down freeway, usually works, blowing cold air, but if car sits in sun for a while, no ac at all just hot air. This morning when it was sitting in shade and cloudy day ( I am in Texas) the ac seemed to work fine once I started driving, but when I came to a stop, it went back to blowing warm air. Also, if I leave the car in the sun or drive it in the sun, it does not work. When using the AC Diagnostic, I saw that the value 12 (sun sensor) was sometimes ranging from 5-8 volts, isn't that a little high?

After some trouble shooting, I think it my evaporator temperature sensor is not working as well.

My readings for the evap temp sensor using the a/c diagnostic was 97 degrees, really high. Sometimes it will go lower, example when the ac starts working on highway, it will display around 47-50 but most of the time, it is in the 78-100 range. I did realize my ambient temp sensor on the front bumper is missing, hence why when I check the temperature on my dash, it sometimes shows 185?

Also, once car is in sun for too long, and trying to run ac, the battery/alternator warning light comes on, visit workshop display faulty warning, and sometimes the hi beams come on the dash and stay on, have you heard of this before?

I have attached a picture of the warning messages that appeared once I was driving the car in the hot sun for a while. You can see that the hi beam light was stuck on (middle of the day). Once I went home, shut car off and started up in the morning, everything was gone.

Any help or insight would be greatly appreciated, thanks so much.
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post #2 of 16 (permalink) Old 06-25-2019, 10:10 PM
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Good question what is the reason, what is the result.
I'd start with elimination of charging issue. How many miles on alternator brushes?
Once you solve charging problem, you can troubleshoot AC par You are being redirected...
The first sensor readout is for checking calibration, the 2nd for checking compressor performance.
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post #3 of 16 (permalink) Old 06-26-2019, 08:34 AM Thread Starter
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The alternator has not been changed. When I had them checked out, mechanic said everything was fine with both.

I checked some things today, I don't believe the compressor is kicking in. Could this be because of a sensor needing replacement or maybe low refrigerant?

With the link you provided, I cannot do the first test, is there a way to do that and bring the codes up on W203, 2001 C320?

Thanks,
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post #4 of 16 (permalink) Old 06-26-2019, 11:39 AM
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I am not familiar with C class, but all other MB class I know have the same logic for AC troubleshooting.
The way to read the sensor varies between the models, but it is still the same system with slight variations.
But low voltage very likely is the reason for AC to shut down, so you need to figure it out first. Mechanics are not expert electricians, so it is up to you to monitor the voltage. Lot of modern models allow displaying voltage on cluster, if not, few bucks buys a gauge that you can plug into lighter socket.
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post #5 of 16 (permalink) Old 06-26-2019, 09:27 PM
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This could be due to a slipping serpentine belt. The idler and/or tensioner pulleys can fail and cause the belt to slip and not drive the alternator or compressor adequately.

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post #6 of 16 (permalink) Old 06-27-2019, 06:55 AM Thread Starter
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Thanks guys. I took the car to my indy shop yesterday and waiting to hear back. I mentioned all that you said on here. They are taking a look at the AC and the Alternator this morning. I have not yet changed the alternator on the car, 120K miles. They did say it seems to be working sometimes but are still running tests. Will keep you posted.
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post #7 of 16 (permalink) Old 06-27-2019, 08:10 AM Thread Starter
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Also quick question, if I can source my own parts, what is a good alternator to purchase? Is it okay to get a rebuilt one? Thanks in advance.
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post #8 of 16 (permalink) Old 06-27-2019, 08:06 PM
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With a rebuilt alternator, it's going to come from China. If this were a DIY job, I'd say go for the rebuilt unit, especially if it comes with a lifetime warranty. So what if you have to replace it every few years? It's 1/4 the cost of a new one. But since you are paying a shop for labor, I'd recommend a genuine new OE or OEM.

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post #9 of 16 (permalink) Old 06-28-2019, 08:18 PM
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Surprisingly, I found that a new alternator for my car, 2005 C230, wasn't that much more than a POS rebuilt.

For the OP, it seems like some new alternators are actually cheaper, because of there being a core fee for a rebuilt (and we know that the core fee always gets eaten by the customer, because shipping back is $$$ and a hassle).

https://www.rockauto.com/en/catalog/...generator,2412



Looks like the Remy may be a good bet:

RockAuto:
REMY 94119 {Click Info Button for Alternate/OEM Part Numbers} Premium; New Info
$116.89
S&H ~$8, depending on zipcode


Amazon:
https://www.amazon.com/Remy-94119-Ne.../dp/B00IZYRJ84
Remy 94119 New Alternator
Price: $125.78


Fwiw, unless I need something *NOW*, for the past few years, I've gone back to mainly buying from RockAuto, and have never regretted that decision.
Plus, you get a free RockAuto magnet.

(Below is from another post by someone else)



Good Luck!
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post #10 of 16 (permalink) Old 07-01-2019, 09:25 AM Thread Starter
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Originally Posted by rudeney View Post
With a rebuilt alternator, it's going to come from China. If this were a DIY job, I'd say go for the rebuilt unit, especially if it comes with a lifetime warranty. So what if you have to replace it every few years? It's 1/4 the cost of a new one. But since you are paying a shop for labor, I'd recommend a genuine new OE or OEM.
Thanks Rudeney, I will be hearing from shop today and update on this thread.
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