doctorroboto

2008 R320 I bought last year, previous owner had recharged the system just before I bought it and did a leak check that was unsuccessful at finding a leak. AC blew cold when I bought the car October 2019. First warm day of 2020 I tried it, and the AC doesn't seem to be doing anything. I don't hear the lines cycling coolant, and the low pressure line feels warm to the touch. I tried to recharge that, and it read basically full, but I don't think it's pumping coolant through the lines, so that's probably a worthless exercise.

I tried to do the reset of the AC system but I can't get that process to work - no blinking lights when pressing defrost + recirc in any combination, with key in any position. Not sure if that even would help, but the car isn't throwing a visible error so I am not sure it knows there's a problem.

When I hit the AC button, the radiator fan definitely spools up, and while sitting there the blower motor seems to change speeds while on max cool quite a bit, but I don't believe the compressor is running.

Does this model have a variable speed AC? Can I tell if the compressor is running just by looking at the hub where the belt engages? I can't even locate it, since I don't see any part with a central hub inside of a pulley that would be spinning independently.

How can I try to diagnose this without a STAR reader? I checked what I believe to be the relevant fuses (including the SAM ones I saw somewhere in a posting) and they are all still showing continuity, so I don't believe that would be it.

Plutoe

You need to visit a shop and confirm that you do in fact have a filled system. The AC shop will put a set gages on and you will have answers quickly!!

doctorroboto

It might come to that, but I'm still trying to determine why the system isn't circulating AND there's no apparent error. It seems odd that the car wouldn't throw a status message at me, or why I couldn't do the AC reset.

Are there any other steps I could check at home prior to bringing this to the shop?

E55Greasemonkey

Get a professional diagnosis before you make it worse.

places

I think by the time you figure it out - assuming you do - you would have been better off taking it to the dealer. Just save yourself the hassle and take it in. You might end up making it worse for the sake of a few dollars.

doctorroboto

Well, I'm happy to explore - I'd like to invest in a decent code reader and have no issue learning more about the vehicle. I also see some notice about a possible bad ground in the passenger footwell, with a service bulletin to replace a wire with a 2-lead wire - is that something straightforward I should check?

E55Greasemonkey

You can buy a scalpel but that doesn't make you a surgeon.

places

That's my thought. Keep digging and eventually it's a mess. Let the pros handle it.

doctorroboto

I would have hoped that forum members would aid new members in helping them think through the troubleshooting process from their experiences, rather than immediately criticize people with an interest in maintaining and learning about their vehicles. So that's disappointing.

I'm totally fine taking it to a shop, but would like to eliminate some of the obvious, simple problems before wasting my time and money to have a shop fix the basic things. Getting the high side pressure checked seems like a good idea, and that's probably in my future soon. I'll go ahead and check the compressor ground point for continuity first, and if anybody has other useful thoughts on basic things to check, I'd gladly consider those as well.

B34chBum

If the compressor is failing you won't see any codes.
You need to beg borrow, or steal a set of a/c gauges, or take it into an a/c shop - the gauges don't lie.

The a/c system (, really the body control system) will protect the compressor if the cooling fan is not operating correctly, and you would see errors/codes associated with it.
I replaced compressor in my car about a year ago.
We had seen occasional difficulty cooling at a standstill the previous summer.
I got lucky in that my local indie shop offered to pump down / recover the refrigerant, sell me the compressor and oil, and recharge system afterwords for a nominal fee.

No problems with it since, knock on wood.

Compressor is accessible from below with car on ramps.
Serpentine belt comes off first of course.
For visibility I loosened the power steering pump reservoir to move it out of the way some. Not sure if I loosened the ps pump itself but don't think so.
Remove air filter and air inlet ducting on the driver's side
I recall one of the a/c hoses and/or the mounting bolts were awkward.
If you have leaks from oil filter housing or ps pump lines, really anything in the area - it will likely be a mess.
You'll want to be sure to have the hose connections clean, and an accurate measure of PAG oil into the compressor. I think it was about 2 ounces, but search for that.
You want to get only a new Denso unit, accept no substitutes.

If you like I might be able to find the part number.

Having said all that, if you don't want to cuss take it to an a/c shop.

flthere

I just had a mechanic look at my a/c issue. It blows cold air for like a mile at the most, and then it'll be warm air. This mechanic looked thru, found that there is no freon, and then recharged it (just below the recommended level), this time it blew cold air for like 6 miles before it started blowing warm air again. He spent like 2 hours on the whole diagnosis, and says that everything he checked on the system is good, including hoses, no leaks, compressor is good (this has a non-clutch type), condenser/evaporator all good), and the only thing he is suspicious about is the climate control unit that is in the dashboard. When it start blowing warm air after setting the temp at 72, decreasing the temp does not kick in the compressor even when it's down to 60F. (the LED moves nicely, it's not one of those issues where the LED light does not move on the temp control wheel). Neither do the fan start spinning indicating that the cooling system is not kicking in. This mechanic says that it's very common mercedes issue that this climate control unit behave this way.

Anybody experienced failure with the climate control unit? Or is it possible that some fuse is on its way out? Or could there be a temp sensor which is falsely setting the temp to like 60 and never letting the compressor kick in? This issue is killing.

The new OEM unit is $1300 according to the dealer :-(

flthere

The mechanic just texted once a new panel is put in, it will need to be programmed by the dealer, is that true???

doctorroboto

Hey, I can't comment on either the programming or the unit having a faulty temp sensor, although I feel like I saw something in the forums in trying to diagnose my problem about bad temp sensors. That said, I know there's temperature sensors in the vents themselves, not just in one place, so it's likely not the sensors themselves, it's probably something in that control computer.

To close out my prior issue with the AC not working, the issue was diagnosed as a failed compressor. There was coolant in the lines, it just was dead. So the shop swapped the compressor and it's been blowing ice cold ever since - very happy with the improvement. I will note that in the process of this I purchased an iCarsoft MB v2.0 car scanner tool, which does read the air conditioning (Climate Control Module). I had it pull the refrigerant pressure before and after the repair. Beforehand, it read 1 bar - empty, or environmental pressure. After the repair, I could see the refrigerant pressure cycle as it expanded and was recompressed, cycling between (I think) 150 and 230 psi. So that's very encouraging, and now gives me an initial condition with a freshly repaired / recharged system, to see what kind of pressures I'm reading down the road. Strongly advocate for the MB v2.0, which cost me something like $150 but has immediately been worth more than that in preventing extra diagnostic time at the shop.

Thanks to the replies leading up to the trip to the shop - it was not a shade tree mechanic project to fix a leak or a relay for my R320.

flthere

Another shop ran thru the diagnostics, determined that the cooling system is good, compressor is working and when the a/c blows cold air (albeit for like 3 min or so on cold start), the pressure readings are good as they should be.

He determined that the a/c heater control unit in the dashboard is acting up and he has seen them go south on MLs. He has taken the unit out of my car, connected it to a known-working-compressor-system and came to the conclusion. New unit is $900 it seems, but he is going to fetch a used one and try it out once.

The a/c works on cold start for me for like 2 or 3 min. But just ambient air afterwards. It's as if the thermostat in the car that determines the temp inside the car is stuck at like 65 degrees, that it never allows the compressor to start working and pump cold air in.

flthere

Just wondering how did they determine that it's a failed compressor? I just returned from the shop, he ordered the a/c control unit and replaced/reprogrammed, but still it doesn't start blowing cold air. He thinks it's a failed compressor and gave a quote of $1065 to replace the compressor ($710 just for the part). My concern is what if it's not the compressor that failed.

B34chBum

A/C gauges read refrigerant pressures directly, and quickly show whether the compressor is working normally.

Your shop may be including the cost of a receiver/dryer in the parts, and they likely have a markup on the compressor.
I was told when mine was replaced that the expansion valve seldom fails, with the style of compressor used.
We didn't replace that, or the receiver/dryer, and it's been fine since (over a year now).

My shop sold me a new Denso unit and I did the swap, the shop also recovered the refrigerant and refilled system when I was done for a nominal charge.

Prerna

Mine was refilled about a year ago. Lately, it suddenly stopped working. I can still switch it on, and there will be noise, like a light whistle but no cool air at all. Any clue what I can expect?

efzauner

I also have AC problems 2011 R350.
I purchased it used under warrantee.. The previous owner already had the AC fixed, a leak in the lines to the 3rd seat.
The problem I had was the left side dash vents where warm, The right side cold. Dealer fixed same leak. Said it cost $2400 lots of labour under warrantee. but its acting up again after less than 3 years. I wonder if they fixed it or just topped up the refrigerant.

yet my C240, 2005 cools like an arctic blizzard! never fails! best AC I ever had!

flthere

That sounds more like a compressor issue from what I read so far.

flthere

Just trying to debug a bit more myself and found that the AC Pressure switch failing may also cause the same issue, where it blows cold air for 1 minute or two, and then warm air. Did any of you ever have to replace the 'Refrigerant pressure sensor/switch'?

GLO

I just had my fan belt replaced after a MB factory recall and spotted a nick in the fan belt.
Stupidly I forgot about it and it failed a month later (it's the 3rd car and only get used when all 6 of need to go out together.)

naturally it failed and made a mess of the engine bay and power steering was impacted.

but after replacing the belt, now our AC won't get cold at all.

could anything have been bumped or not plugged back in? That would stop the compressor from kicking in?

like the opportunity, no errors and there is no load thst kicks in like usual when AC is turned on.

doctorroboto

I think you might want to question if the belt failed because it had a nick, or if it failed because of why mine failed - the AC compressor locked up, and took out the belt in the process. Can you define "made a mess of the engine bay"? Is there melted belt everywhere (on the idler pulleys), or did it just snap and throw bits of belt all over the place? Was there a whining sound before it went? I might inspect if the compressor pulley spins freely, and have the shop check if there's refrigerant in the lines and such. If not, or if that bearing is shot, you're in for an exciting ride the next time you get a belt back on there.

If the belt legitimately just snapped, I have no idea what's wrong. In the 5 years I've had my R320, I've now replaced the compressor twice, which is annoying. But the second time was after it sat outside in the baking sun for 3 months waiting at the MB service center for the brake booster repair, so I'm writing that one off to dried out seals due to disuse and improper storage, and dealing with it.

Is this for the R320? What year is it? I have a "2008" with a date code from 2007, and it was a disaster getting my shop to put the right year parts on there with the 8 groove belts and the proper compressor. He ended up putting the 7 groove belts and associated compressor on, but the rest of the system can take 8 grooves, and it was a huge thing dealing with getting that sorted out.

GLO

Mine is a 2009 but 2008 build.
I have refridgerent and it appears its the TXV valve as the pressure is to high and it shuts the AC down.

The mess i was referring to was the shredded fan belt. Missus was driving when it disintegrated on the motorway. She did very well to get 95% of the way home wothout power steering.


Oddly I noticed the knick in the fan belt after MB dealership addressed a recall issue.

B34chBum

Update: Spring/summer of 2023 my A/C would do as described early in this thread. (4 year service life?)
, with it cooling marginally well from a cold start in the morning then hit or miss during the day.
I'd find that sometimes in the heat of the day if I turned the dial down to a stupid requested temp, it would cool long enough for me to do a short errand but then blow ambient afterward.
(Especially after a restart)

Shame on me I guess for waiting so long to check it out, but Florida summers (and Falls now) are demoralizing with the heat..

I've read on another thread I think for gas-specific model, that there is a ground point behind the passenger-front kick panel which gets poor connectivity and makes the control panel misbehave.
I will look for it and clean any corrosion I might find there, and report back if it makes any difference.
I've also bought a kit including compressor, condenser and receiver-dryer, valve blocks, seals. And a replacement suction hose, the one which drops down beside the left exhaust - in case it has collapsed inside.

I'm currently in the middle of replacing the PS pump, radiator, left motor mount and hot side boost hose.
Since the bumper cover is still off I might as well spend another few hours refreshing all that stuff while I have good access.
When the PS fluid line to the radiator was leaking, a fair amount was sucked around forward by the radiator fan, making about 1/10th of the condenser greasy/grimy/plugged up.

I haven't seen any 9006 code throughout all this. (That's the one indicating a bad compressor solenoid valve / diode failure)

@doctorroboto I've seen this type of issue as well (I have the 8-rib belt from the pre-MY split, as well). My misadventure began with putting a 7-rib harmonic balancer pulley on (my mistake ordering part)
The belt didn't break but would peel off 1 rib's worth on one edge or the other.
I had a hard-starting issue as well, and one shop I took it to wouldn't work on the car at all, swearing that I had the wrong PS pump on it.
(He had it backwards!)
The 8 rib balancer pulley is more expensive and a little harder to hunt down. Of course!

Anyways, will see.