'02 C240 AC warm at idle - Page 2 - Mercedes-Benz Forum
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post #11 of 33 (permalink) Old 06-11-2019, 09:51 PM
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Originally Posted by Hirnbeiss View Post
If AC works fine at speed, this suggests that there could be a problem with the fan(s). Check the function of the fan clutch.
Looks like I'm "corn fused" as usual.. Seaglass says he installed a new aux fan assembly, Hirnbeiss says check the fan clutch,.. Rodney, says it's the single fan system.. Oh-well.. What ever kind it is.. Check it, to make sure it's working...
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post #12 of 33 (permalink) Old 06-12-2019, 04:49 PM Thread Starter
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Bobby you win because you were the closest. You were right about most everything except that Seaglass is a she and not a he. So, I hope I did not break any codes here but I gave up and booked an appointment at the local dealership. Please forgive me but it is in the low 100's here in Arizona and my Benz is black on black! Therefore, diagnosis is the expansion valve and compressor with disclaimer clause of a condenser, dryer and clutch thrown in for good measure. At an estimate of more than the value of my beloved C240 I fear I will be forced to sell her to someone who can do the work themselves. I enjoy doing what projects I can myself (ie: recently replaced shattered sun roof slider) but this is beyond my skill level. It breaks my heart to consider letting her go. I was hoping to drive the wheels off her but now I must consider selling or moving to the Upper Peninsula of Michigan where I won't need the AC.
post #13 of 33 (permalink) Old 06-12-2019, 04:54 PM Thread Starter
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It was diagnosed as such from last German auto shop so I did however, it did not change anything - except that I am $145 lighter in my wallet.
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post #14 of 33 (permalink) Old 06-12-2019, 04:58 PM Thread Starter
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It was diagnosed as such from last German auto shop so I did however, it did not change anything - except that I am $145 lighter in my wallet.
Sorry, this is in regard to the recharge comment
post #15 of 33 (permalink) Old 06-12-2019, 06:35 PM
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So before you write it off, here are some things to consider. If it cools well with the engine above idle, i.e. driving down the road at 30mph, then here's what it could be:

1. Inadequate airflow across the condensor due to a defective engine suction fan. You have replaced the fan, so assuming it is running at high speed when sitting at idle with the ACC set on full blast, then this would not be the problem.
2. Inadequate airflow across the condensor due to dust/debris buildup. I assume that the mechanic checked this, but it might be worth a good pressure washing of the condensor if you are in a dusty environment.
3. A clogged condensor. This would only be the case if there was a failure of the compressor and it spewed pieces of itself into the system. Since it's cooling when above idle, that is probably not the case.
4. A clogged dryer (a.k.a. desiccant cartridge). Other than compressor failure, the only reason this would happen is if the system were open to the air. The dryer will quickly absorb ambient moisture and be ruined. If the system never leaked and was let opened to the environment, this is likely not the issue.
5. A bad compressor. This car's compressor does not use a traditional pulley clutch, but instead has an internal "swash plate" that can vary the compression ratio. This could be failing and making it so that the compressor needs a higher RPM to build enough pressure to cool. If revving the engine to 1,500 or 2,000 RPM while in park causes it to cool, then this is a possibility. If revving the engine does not help, then it's a condensor issue. If revving helps, then it's not the condensor or engine suction fan.
6. A bad expansion valve. This valve limits the flow of refrigerant into the evaporator so that only cold gas enters. If the valve fails, it can prevent gas from entering at all. It can fail in such a way that it requires a much higher pressure to allow refrigerant to pass through, such as by running the compressor at higher RPMs. One way to check this is if the high pressure (smaller) hose coming from the compressor is VERY hot, and the line coming out of the condensor is hot, but not scalding. If so, then the compressor and condensor are doing their jobs and the evaporator is not getting cold gas which could be because of the expansion valve.

So, it sounds like your mechanic charged you $145 to vacuum down and recharge the system. That's a good price. I think that it's the expansion valve. If the same guy would charge you a comparable labor rate to replace it and do a recharge, then I might would do that before writing it all off.

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post #16 of 33 (permalink) Old 06-12-2019, 09:13 PM
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Or you know it could be not enough refrigerant and it just needs a recharge. But what do I know, I've only been doing my own AC work on over a dozen cars for the past 2 decades.

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post #17 of 33 (permalink) Old 06-12-2019, 09:28 PM Thread Starter
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Originally Posted by rudeney View Post
So before you write it off, here are some things to consider. If it cools well with the engine above idle, i.e. driving down the road at 30mph, then here's what it could be:

1. Inadequate airflow across the condensor due to a defective engine suction fan. You have replaced the fan, so assuming it is running at high speed when sitting at idle with the ACC set on full blast, then this would not be the problem.
2. Inadequate airflow across the condensor due to dust/debris buildup. I assume that the mechanic checked this, but it might be worth a good pressure washing of the condensor if you are in a dusty environment.
3. A clogged condensor. This would only be the case if there was a failure of the compressor and it spewed pieces of itself into the system. Since it's cooling when above idle, that is probably not the case.
4. A clogged dryer (a.k.a. desiccant cartridge). Other than compressor failure, the only reason this would happen is if the system were open to the air. The dryer will quickly absorb ambient moisture and be ruined. If the system never leaked and was let opened to the environment, this is likely not the issue.
5. A bad compressor. This car's compressor does not use a traditional pulley clutch, but instead has an internal "swash plate" that can vary the compression ratio. This could be failing and making it so that the compressor needs a higher RPM to build enough pressure to cool. If revving the engine to 1,500 or 2,000 RPM while in park causes it to cool, then this is a possibility. If revving the engine does not help, then it's a condensor issue. If revving helps, then it's not the condensor or engine suction fan.
6. A bad expansion valve. This valve limits the flow of refrigerant into the evaporator so that only cold gas enters. If the valve fails, it can prevent gas from entering at all. It can fail in such a way that it requires a much higher pressure to allow refrigerant to pass through, such as by running the compressor at higher RPMs. One way to check this is if the high pressure (smaller) hose coming from the compressor is VERY hot, and the line coming out of the condensor is hot, but not scalding. If so, then the compressor and condensor are doing their jobs and the evaporator is not getting cold gas which could be because of the expansion valve.

So, it sounds like your mechanic charged you $145 to vacuum down and recharge the system. That's a good price. I think that it's the expansion valve. If the same guy would charge you a comparable labor rate to replace it and do a recharge, then I might would do that before writing it all off.
That is a great deal of information and all I can say is THANK YOU!!

Beginning with consideration #2 - Yes, sadly I travel on unpaved desert roads about twice a week.

Next, consideration #5 Yes, I should have mentioned in the original post that revving the engine does cause it to cool but makes the drive thru attendant very nervous. I just want to clarify the last sentence on #5... "If revving helps, then it's not the condensor or engine suction fan." Correct?

Therefore, we are putting our attention on the expansion valve then, correct?
post #18 of 33 (permalink) Old 06-12-2019, 11:51 PM
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So, it sounds like your mechanic charged you $145 to vacuum down and recharge the system. That's a good price. I think that it's the expansion valve. If the same guy would charge you a comparable labor rate to replace it and do a recharge, then I might would do that before writing it all off.
If you were to buy one,.. Expansion valves are around the $30 (and up) price range,.. And pretty easy to install.. (That's for guy or gal, that's set-up to do AC work)..
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post #19 of 33 (permalink) Old 06-13-2019, 05:48 PM Thread Starter
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If you were to buy one,.. Expansion valves are around the $30 (and up) price range,.. And pretty easy to install.. (That's for guy or gal, that's set-up to do AC work)..
I will ask, beg, bribe...my neighbor (mechanic) for help on installing this. Do I need to be careful which vendor I choose for part (s)? Mercedes part is 3x the cost.
post #20 of 33 (permalink) Old 06-13-2019, 08:39 PM
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Yes, revving the engine changes nothing in terms of the amount of air flowing over the condensor, so that rules it and the suction fan out as problems. It still could be the compressor, but also could the the expansion valve. So, given that the expansion valve is much less expensive, that's what I'd try first.

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