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Old 06-06-2011, 06:26 PM   #1
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Intermittent AC. Blows cold while driving...

Fortunately for me as the hot and humid weather is setting in, my AC is acting up. When parked with the AC on, it takes 15+ minutes before it'll start blowing cold air, if I'm driving it kicks in within 5+/- minutes.

Today, on my way home it seemed to be blowing cold air, but it didn't really seem to get that cold. Occasionally when I would come to a stop, the cold air would stop, but air was still blowing, so I don't think it's my blower motor. Sometimes it seems as though the fan speed will jump up and down.

I've had no issues with it over the past year other than having to replace a stepper motor link that was broken. Any ideas? Blower motor regulator? Compressor going out?

Appreciate any input regarding this matter as I do not like going without AC in 90+ humid weather.
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Old 06-06-2011, 09:17 PM   #2
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System likely needs regassing.
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Old 06-06-2011, 11:31 PM   #3
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I'm hoping that's all it is. If i'm low on freon though, does that indicate a leak somewhere?

Also, is there any explanation as to why it only seems
to blow cold while driving? I've read that some systems will disengage if they're low on freon, but the driving part isn't making any sense to me.

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Old 06-07-2011, 10:16 AM   #4
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You could have a slow leak. They will check when regassing. Systems do loose a little gas even without a detectible leak over time. Complete loss of pressure shuts down the system to protect the compressor. Partial gas pressure will give you some cooling when moving due to greater air flow & thus heat transfer through the Consensor at the radiator.
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Old 06-07-2011, 06:47 PM   #5
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My car seems to be suffering this as well, or it could just be the extreme heat. I can't recall but it seems to me the A/C used to be more effective. Lately it has been mid-90s every single day here.
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Old 06-07-2011, 09:04 PM   #6
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Matt - Aircons need regassing from time to time.
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Old 06-08-2011, 10:56 PM   #7
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Well i had the refrigerant levels and temps checked today and all was in normal ranges. He said if anything was wrong with the system it was probably a sensor or the control unit itself. Any other ideas?
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Old 06-09-2011, 10:05 AM   #8
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Sorry - we had to check the obvious. I note that you state high humidity. Does the aircon start off cold & then get worse & worse with time on? If so you could be freezing the evapourator but then airflow would slowly reduce as ice builds up.

After that we are guessing. Could be a lazy compressor, sensor trouble or controller trouble. You really need to get the car onto a Star. Is the car storing any codes?

Did the aircon guy read the temperatures at the vents & comment?

EDIT - please do a controller reset.

http://www.mbworld.org/forums/c-clas...tic+easter+egg
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Old 06-09-2011, 06:28 PM   #9
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Sorry - we had to check the obvious. I note that you state high humidity. Does the aircon start off cold & then get worse & worse with time on? If so you could be freezing the evapourator but then airflow would slowly reduce as ice builds up.
Other way around. Starts off just blowing hot air and gradually gets colder after I've started driving. On cold starts in park, it takes upwards of 20 minutes before it'll start blowing cooler air. It's almost as if the compressor kicks on, but quickly shuts off a few seconds later. As long as I'm driving it'll blow cool air, but if I come to a stop light it starts blowing warm again.

Quote:
After that we are guessing. Could be a lazy compressor, sensor trouble or controller trouble. You really need to get the car onto a Star. Is the car storing any codes?
Star will come soon if I can't figure anything out. I haven't checked for any stored codes yet, but I can. No CEL's or any other warning lights are present.

Quote:
Did the aircon guy read the temperatures at the vents & comment?
As far as the temps, he took readings vent-side within the car and temps of the lines in the engine bay. They were within the 45C range and he said that those temps are actually pretty good/ normal. He also noted the condensation on the lines in the bay.

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EDIT - please do a controller reset.

http://www.mbworld.org/forums/c-clas...tic+easter+egg
I've done this procedure a couple of times already. When I had the broken stepper motor link the cycle wouldn't stop, but since being replaced it cycles for about 28 seconds and then shuts off. So I assume all is well here.

Other than that, a friend mentioned his dads Chevy Avalanche was doing something similar and it ended up being the fan not working properly. However, the fan does come on, but I dunno if it's working "properly." Car temp is usually around 95C and the battery hovers around 13V in dyno mode.
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Old 06-09-2011, 08:35 PM   #10
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It could be the fan controller. If you are not travelling fast enough to get enough air through the condenser then the fan has to come on & do the job.

It's not right. It should get cold at the vents immediately. It should have no trouble at all holding the interior of the car at below 20 deg C or 68 deg F.

I hope all the diverter flaps are setting themselves correctly.
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Old 06-09-2011, 09:17 PM   #11
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My car's A/C performance is no where near as bad as described here, so I think it is just the extreme heat. Set to max cool which recirculates the air, my car will blow ice cold even at a stand still. It is just taking longer to cool down the inside due to the mid-90s and very high humidity in GA lately.
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Old 06-14-2011, 12:20 AM   #12
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Ok, so after a lot of googling....

Is the fan supposed to run at all times when the AC is on? I've read that other makes/models have had this problem and several state that it should, but I haven't come across any MB specific answers. If that's the case, I just tried it with AC on full blast and it wasn't spinning. No cold air as well. My engine bay has seemed a bit hotter than usual lately, but that may just be due to the 90F+ temps...

If it's supposed to be on, any way to tell if it's the actual fan or the fan motor? Or are they both one unit?

Third, if I replace either of the two, will STAR be required?

Thanks to any help!
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Old 06-14-2011, 06:07 PM   #13
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Bump.

Can anyone confirm any of this?
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Old 06-14-2011, 06:23 PM   #14
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My fan runs the minute you switch on the a/c. Fan speed is controlled by the fan controller with input from the a/c pressure/temp sensor & the main dash a/c controller.
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Old 06-14-2011, 07:01 PM   #15
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My fan runs the minute you switch on the a/c. Fan speed is controlled by the fan controller with input from the a/c pressure/temp sensor & the main dash a/c contoller.

Thanks Glyn. I'm gonna keep an eye on it for the next day or so because when I had the guy check the freon levels/temps the fan was working at the time.

Can I hook the fan to a 12V power supply and see if it'll spin or can that do more harm than good?
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Old 06-14-2011, 11:40 PM   #16
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Quote:
Originally Posted by Glyn M Ruck View Post
My fan runs the minute you switch on the a/c. Fan speed is controlled by the fan controller with input from the a/c pressure/temp sensor & the main dash a/c contoller.

mine runs the whole time ac is on
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Old 06-19-2011, 12:58 AM   #17
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Well I tried reseating the cable harness going to the fan and it's now working again. I had tried this before, but I guess this is probably why it stopped working for a short while. So it appears to be working just fine, I've noticed the variable speeds. However, the car's still running in the 95-100F range. I've talked to my friend who has a C350 who lives in similar climates and his is staying around 90F like it should be. I'm overheating, even with the fan working. Coolant level seems to be fine.

I've located the AC temp switch in EPC, but it's connected to the condensor so I'm guessing the freon will have to be drained to remove this? I'm going to pull the climate control unit back out and double check connections there since it was removed for the stepper motor link replacement.

Just trying to exhaust all options and pinpoint the problem before having to take it to the stealership.
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Old 06-19-2011, 04:19 AM   #18
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You mean 90C, I assume? Is this really considered overheating? I thought that was in the high normal range depending on ambient conditions. Then again, aside from a week with a failed thermostat resulting in running too cool, my car has never got above the 90C mark even on the hottest days.
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Old 06-19-2011, 03:57 PM   #19
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You mean 90C, I assume? Is this really considered overheating? I thought that was in the high normal range depending on ambient conditions. Then again, aside from a week with a failed thermostat resulting in running too cool, my car has never got above the 90C mark even on the hottest days.
Sorry, yes you are correct Lilbenz. It may still be in the normal range, I've just always heard that these cars are pretty consistently around the 90C mark. I've only had the car for about a year now, but I've never seen it this high before.
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Old 06-26-2011, 09:29 PM   #20
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Does anyone have access to the A/C values taken from the climate control unit? I can find them for other models, but none specific to the w203.

Holding down the rest button, I'm able to pull up values, but dunno which is which by cross-referencing other platforms.
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Old 06-28-2011, 12:59 AM   #21
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Typical HVAC compressor high side working pressure is approximately 20 bar/290 psi.

Replacing a faulty B12/2 pressure sensor restored my (leak-free) system to its full efficiency. Seldom gets much above 80 Fahrenheit ‘round here though.

Click the image to open in full size.



Shown in situ on lower portion of external condenser plumbing:

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Old 06-28-2011, 11:28 AM   #22
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Something still seems not right with mine. Once it gets cold it is fine, but it takes longer to get there these days than I remember.
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Old 07-07-2011, 08:17 PM   #23
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*UPDATE*

Sent the car into the stealership last Saturday morning. I had to have an ESP error checked as well which ended up just needing a reset due to it losing communication. I sent the car in for their "AC special" which included an evac and refill and an inspection of AC components. They evacuated the system, reoiled, and filled it. I was told they were having trouble communicating with the "control unit" so they needed another day with it. They gave me a loaner and sent me on my way. Being the holiday weekend, they wouldn't get back to it until Tuesday. Tuesday rolls around and I never hear from them so I called. Still no solution. Finally 10 minutes before they close, they call and state my car is ready, but I couldn't make it there before they close so I opted to pick it up the next day after work. Wednesday - I go pick up the car and I'm told they found the radiator fan inoperable and all it needed was a software upgrade. Everything's working. Temps back to normal, AC working like it should, etc.

Today (Thursday) I go to leave for work in the morning and the car wont start. Awesome. Finally get it jump-started and all is well again. Drive to work and go out to check it on my break. Dead again! So I took it back to the dealership and they said the only conclusion they could come to was that it was my battery - 5 years old. $188 later and only time will tell now at this point.

Anyways, here is what the invoice stated:

"FOUND RADIATOR FAN INOP. SDS TESTED. TESTED FAN FUNCTION, GOOD. CHECKED POWER AND GROUND AND PWM SIGNAL. FOUND NO PWM SIGNAL FROM MESFI. UPDATED AND SCN CODED. FUNCTION TESTED. GOOD."

I'm going to call back tomorrow to confirm, but what is the "MESFI"? My car is tuned which is why I'm curious to know if they reflashed the ECU and/or is the reason behind all of this...

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Old 07-08-2011, 08:58 AM   #24
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ME-SFI = Motor Electronics - Sequential Fuel Injection

Benz speak for part of what you call the ECU.
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Old 07-08-2011, 01:27 PM   #25
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So "part" of it....is it likely the tune was erased? If so, i'm going to be done with it and work on just seeking a refund.
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Old 07-08-2011, 01:27 PM
 
 
 
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