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AC flow decrease and stop working until i cut off AC and restart after few minutes
hello MB friends
i have a little issue on my 2013 w212 350 cdi 4matic...
on hot day , when i put my AC on auto for a long trip , air flow start to slowly decrease after 20-30 minutes , and at a time there no air flow at all on air vent.. if il try to use manual setting for AC , and put blower to max speed , there is no air flow on air vent but i can hear the blower on the dashboard running hard.
after that , if i cut off the AC , en st air flow setting to front and speed 4 ( for example ) , air flow start to increase slowly , and reach normal flow after 5 - 10 minutes ... air is cold for 5 -10 minutes too ...
and when i put AC ON again , all is ok but it start to decrease after few minutes..
for me it's like something is freezing on AC system and stop air flow until i cut it off .... and de-icing
maybe someone have same issue and a solution
thx for reading ( hope you can understand my english " )
The symptoms sure sound like a freezing EVAP.
Get a decent scanner, Launch Creader Elite for Benz...cheapest but most powerful for the money for BENZ ONLY.
When car has shut down for 12 hours, read all the temperature sensors at N22/7 HVAC computer. Engine OFF, only ignition ON.
There will be EVAP temperature sensor there. See what value it is reading against all other temperature sensors.
Hopefully it shows drifted value even at ambient temperature of what you have now. 2C difference is OK.
MB setting for EVAP maximum cold is no colder than 2C to prevent freezing.
Run the HVAC and see how how low does the EVAP temperature sensor read till the moment EVAP frozen ( no air flow ).
There you can see its actual drift value.
Perhaps with that baby Launch you may picked up trouble code if any.
Starting with sensor calibration test, as S advise is the easiest way to troubleshoot and that will also give you static charge of refrigerant,
Than for compressor test you need hot day as variable speed compressors need to be forced to max for proper output reading.
My bet is a freezing up EVAP coil underneath the center stack dash. If you pull the cabin filter from the passenger side footwell and get a tube camera from a tool shop, fish the camera into the duct work that is closest to the center stack, you'll likely get a view of the eval coil to take a look. You may need a cleaning if it's all gunked up with dust and crap like that. If it's clean, then you probably have a leak in the cooling line or compressor. When coolant gets low in HVAC, the coils will freeze over. Same on your home units too.
See if you can get a cheap tube camera and snake it into the duct work to see it, would be where I would start. Also pretty easy to have the ac pressure tested to see if you have a leak (you'll know if the pressure is low).
Another way to check if it’s freezing over - when airflow stops or noticeably reduced, turn off the ac and turn up the heat. If airflow improves after a few minutes, you’ll know…
Hi, did you manage to find out what was causing the issue with your AC?
I have the same issue on my ML W164, when I start the car and turn on the AC it is blowing cold air as it should be but after a drive, sometimes 1-2 hours other times 15-20mins, the air flow decreases as you described and almost stops. When I try to increase manually or with setting new cooler temperature, the fan noise in the dashboard starts to increase but not much air coming from the vents, seems like the vents are not opening and allowing the air to enter the cabin.
When I stop and without turning off the car or put it on park, everything starts working normally ... for some time until the issue appears again.
I will try scanning it with diagnosis for error codes but wondering if you already found out solution.
Thanks!
Hi, did you manage to find out what was causing the issue with your AC?
I have the same issue on my ML W164, when I start the car and turn on the AC it is blowing cold air as it should be but after a drive, sometimes 1-2 hours other times 15-20mins, the air flow decreases as you described and almost stops. When I try to increase manually or with setting new cooler temperature, the fan noise in the dashboard starts to increase but not much air coming from the vents, seems like the vents are not opening and allowing the air to enter the cabin.
When I stop and without turning off the car or put it on park, everything starts working normally ... for some time until the issue appears again.
I will try scanning it with diagnosis for error codes but wondering if you already found out solution.
Thanks!
I might check the drain tube first, mine clogged up once on a 2000 mile trip, as soon as I unclogged it, it stopped, it was the same symptoms as yours, A/C fine until Evap coil froze, then A//C off just air until it started blowing air again, the temps outside were 95-105 so no need to turn on heat. Is water dripping out underneath the car with the A/C on?
Last edited by pierrejoliat; Sep 4, 2024 at 09:54 AM.
Hi, did you manage to find out what was causing the issue with your AC?
I have the same issue on my ML W164, when I start the car and turn on the AC it is blowing cold air as it should be but after a drive, sometimes 1-2 hours other times 15-20mins, the air flow decreases as you described and almost stops. When I try to increase manually or with setting new cooler temperature, the fan noise in the dashboard starts to increase but not much air coming from the vents, seems like the vents are not opening and allowing the air to enter the cabin.
When I stop and without turning off the car or put it on park, everything starts working normally ... for some time until the issue appears again.
I will try scanning it with diagnosis for error codes but wondering if you already found out solution.
Thanks!
I might check the drain tube first, mine clogged up once on a 2000 mile trip, as soon as I unclogged it, it stopped, it was the same symptoms as yours, A/C fine until Evap coil froze, then A//C off just air until it started blowing air again, the temps outside were 95-105 so no need to turn on heat. Is water dripping out underneath the car with the A/C on?
yes, water is dripping. Will try to turn on the heat or just some air and see if this will work until the Evap coin unfreezes if that is the issue.
yes, water is dripping. Will try to turn on the heat or just some air and see if this will work until the Evap coin unfreezes if that is the issue.
Hi again,
after monitoring when the issue occurs it turns out it appears only when I drive constantly with more than 2000rpm, maybe on a highway. If I am in the city and driving in the traffic, constantly stopping there is no issue.
I noticed that the clutch is always engaged with the pulley and serpentine belt, is that normal even when the AC is off? From other cars I know it should not be when the AC is off.
Checked the system for gas, there are no leaks and there is enough gas in it.
However the compressor always gives constant pressure even when the AC is off, a little less when we turn on the engine, can’t remember the numbers.
Also checked the car with STAR and there were not error codes but this message came on the picture.
We tried to change the valve on the compressor but it is still on constant pressure and freezes the system.
Does anyone knows what this bulletin is for, I can not find info on internet for it.
Could it be the clutch that is making the problems or is it the compressor itself.
Thanks! Star info This is how it freezes everything
- TXV bulb sensor should not allow coil to freeze that much...
-- AAC is solderless module!
Frozen low pressure side has the potential to send liquid refrigerant into compressor... that's destructive.
Hi,
Thanks for replying!
My mechanic also checked the evaporator sensor, I think it is the same you are referring to TXV bulb sensor and it was around 40F, location under the steering and behind the central console where we could reach it. When taking it off the evaporator it was reading the outside temperature correctly so it is working fine.
Just checked on other W164 and the compressor is always engaged, so this is wrong assumption of mine.
Frozen low pressure side has the potential to send liquid refrigerant into compressor... that's destructive.
I have the car for a couple of months, if the previous owner drove it like that for a long time indeed it might caused damage to the compressor. Still trying to figure that out, if this is the main issue.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Most, if not all, HVAC techs are going to tell you that you are low on refrigerant when the pipes freeze like that. I didn't read all the responses, but did you have your A/C professionally looked at?
At the very least, get some A/C gauges from Amazon or Harbor Freight and take some measurements. Don't just throw refrigerant at it without knowing if that is the problem. And if low refrigerant is the problem, find the leak. It could even be the Schrader valves for the hi and lo pressure lines.
Most, if not all, HVAC techs are going to tell you that you are low on refrigerant when the pipes freeze like that. I didn't read all the responses, but did you have your A/C professionally looked at?
At the very least, get some A/C gauges from Amazon or Harbor Freight and take some measurements. Don't just throw refrigerant at it without knowing if that is the problem. And if low refrigerant is the problem, find the leak. It could even be the Schrader valves for the hi and lo pressure lines.
That is what they are saying indeed 🙂
but we hooked the AC on the machine and the level of the refrigerant was nine hundred and something. When I look at the specs there should be 970g, so it is not the issue.
Thanks!
I think the high side liquid is not controlled well !!!
Regardless of AAC Module, the TXV itself should never freeze the line... all the way back to compressor.
Perhaps the compressor is running on Max non-stop due to a control issue. AAC module use many temp sensors for feedback... yet keeps on building pressure... that's really odd!
We assume the compressor has both clutch + proportioning valve to control it... perhaps this one does not.
Can't go wrong with a full chassis scan then AAC data collection then a physical.
Last edited by CaliBenzDriver; Oct 29, 2024 at 06:00 PM.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by Sandockan
That is what they are saying indeed 🙂
but we hooked the AC on the machine and the level of the refrigerant was nine hundred and something. When I look at the specs there should be 970g, so it is not the issue.
Thanks!
I don't know. There should be a label stating the amount to use +/- an adjustment amount. If the specs say 970g +/-25g (or whatever) and you have 910g, then you don't have enough. You need to be precise when it comes to this stuff.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Can you provide your VIN or full model number (212XXX)? I need to enter it into WIS to make sure I am looking at the correct data, but from what I see the amount of refrigerant to be from 590g to 690g based on the model.
Assuming I am looking at the correct data, you are WAY overfilled at 970g. There is usually a pressure switch that will disable the compressor if you are that overfilled.
Last edited by JettaRed; Oct 29, 2024 at 08:30 PM.
Can you provide your VIN or full model number (212XXX)? I need to enter it into WIS to make sure I am looking at the correct data, but from what I see the amount of refrigerant to be from 590g to 690g based on the model.
Assuming I am looking at the correct data, you are WAY overfilled at 970g. There is usually a pressure switch that will disable the compressor if you are that overfilled.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Thanks. I had the wrong model, etc. You are correct; the fill capacity is 970g. But we still want to be exact in how much was measured. BTW, your model number is 164.186, which is your ML350. I missed that in your first post, so I was looking at an E-Class model. The attached doc might help.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
AC flow decrease and stop working until i cut off AC and restart after few minutes
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