amoffitt

Hello guys,

I have had an issue with my 2009 C350. Sometimes when you start the car the A/C system blows hot. After a couple of times of turning it off and restarting the car it will blow cold air like normal. I did research a little bit but I did not really find anything helpful. My service advisor said that it sounds like the compressor is going out but I am not sure how accurate that is since it still blows very cold when it is working correctly. Has anyone experienced anything like this before. The car has 109K miles on it. Thanks in advance.

stgry1

I have the same issue and have researched this quite well. Our A/C Compressors do not have an external clutch so all operation is completed internally. Turning the system on and off is rather ineffective as our compressors are in a constant state of engagement. This may sound odd but try this...When the unit blows warm, try to accelerate a little more agressively then normal. For me, higher rpms tend to get the unit functioning properly. There are times when acceleration is not an option so I downshift a gear or two and try to keep the rpms above 2k...I've pretty much got it down pat until I decided to fork out the 1k on a new compressor and installation. Hope this helps.

Acapulco Bill

C300 Sport also, twice the A/C blew hot when first turned on. I stopped the car, turned off the ignition, then restarted the car. Worked fine after that. May be a faulty relay, or the vent that "blends" the hot and cold air to control the air temperature was stuck in the "hot" position. As summer has finally arrived, will keep a eye out for erratic behavior.

amoffitt

I haven't tried that approach. It is usually right at startup when I notice it and fix it by turning it off and on a few times. I will try that.

To me it would make more sense that a relay or vent would cause this. Im not sure. Ideally I'd like to have this fixed. I should probably check a few relays or something and go from there.

stgry1

Happened again to me this morning. The system blows air but not cold. After 5 minutes of cool ambient air only, I shifted into neutral and increased the revs a bit to 2k. Started cooling immediately and continued cooling properly. My vehicle only has 9k on it so disappointed to say the least but it is 2011 so it sat idle for many months. My issue is the compressor without a doubt. Hopefully it's something a bit more simple and cheap for you.

CGC

I have a similar problem. Dealer diagnosed a "blend flap stepper motor". Only a $74 part, but they want $900 to install it. Has anyone tackled pulling the dash to replace a stepper motor?

stgry1

That was mentioned to me as well but I quickly proved them incorrect. While in the service drive, I had the tech in the car. He mentioned this was the issue. I asked him to turn the climate to high heat. I could have cooked hot dogs in there. I then said please switch back to cold. It then blow cool but not cold. It was obvious no compressor engagement. I then asked him, don't you feel the blend door is functioning?? 'He said ya....but.' I then increased the rpm of the motor to 2k (while idling in park) and guess what, cold A/C. He said, hmm must be a compressor. So be careful of quick quotes. They may be inaccurate.

CGC

Interesting, I will have to try the rpm thing and see if mine does the same.

Josh.A.Hussey

+1

Words to live by!

amoffitt

I tried reving the engine to 2K a couple times and it started blowing cold like normal. So Im guessing I am looking at a A/C Compressor thats bad.

HBguy

To over-simplify, the hvac/r systems operate because of a pressure differential and the circulation of refrigerant. Put it in sport mode and you'll have higher rpms, which make for a higher pressure differential and more circulation.

Now that i have your attention, please kill anyone who even suggests an automotive compressor can go bad. The clutch, maybe.

To the guy who let his car sit, thats the problem. There is a seal that can dry from lack of use on the compressor but as long as you turn it on at least once a week or so, the oils in the system will keep them from drying. Its a mercedes, and even if you bought it used, drive it like it is...use the hvac, and every other feature it has! I've never had a vehicle leak refrigerant ever, that ive bought new and most of the ones ive bought used. A naturally developed leak (from a seal) can reseal with use as long as the leak isnt bad. Ive bought 2 cars that i was told had leaks...used ac nonstop and never needed to recharge.

HBguy

one more thing. Shops replace compressor for any combination of the following:
1. They dont know what they're doing (majority)
2. They dont want to just replace the clutch.
3. They are mechanics, not technicians.
3.a even most automotive technicians would struggle at best to fully understand the refrigeration cycle, let alone each models particulars. Automotive hvac systems are in a sense the most complex to diagnose because it involves ambient air temp, air flow, stop and go engine speeds, internal air temp, and the whole world of clusterfukks resulting from non-hvac guys putting tools tonyour ac system.
4. They dont know how to detect leaks. Trust me, its not as simple as tracing lines with a sniffer.
5. They dont care about fixing it, let alone diagnosing it. They just want to create cold air from the vents.
6. Follow the money.

I suggest that with any hvac issue, always take it to an auto ac specialist who warranties his work....or the stealership (warranry also)

stgry1

I suppose I'm the "guy who let his car sit"? Nice assumption but I actually bought it last year w/ 6k on the clock. Owned by an older man who didn't drive much obviosuly.

Regardless, a compressor can fail for many reasons aside from just a clutch issue. The unit can leak internally or not produce sufficient pressure due to bad reed valves, worn piston rings, cyclinders etc. Lack of lubrication is the leading cause for compressor failures. There could be a leak anywhere else in the system (shrader valve, evap, dryer, etc) which can lead to premature compressor failure. This may not directly pertain to our vehicles components but general statements warrant general responses. So to "kill someone" due to a mention of a failed compressor is a bit much. Oh, and there is more than just "a seal that can dry from lack of use". There are no less than 20+ seals and o-rings in the average vehicle hvac system and any one of them can cause system failure due to refrigerant and/or pressure leak. My system regardless of limited use has never been low on refrigerent, hence no leakage. The issue most likely is the internal PWM soleniod which is not a serviceable part.

HBguy

I dont give a **** who did what. I'm clearly making a greater point about jumping to conclusions. And itonically, its because people love to find quick answers when there are none...the main point you completely missed. If you are a parts changer or a mechanic, thats fine. If people own a Mercedes and want a Mercedes solution, there are no DIY or short cuts with auto HVAC. If you really knew as much as you want to make it sound, you would agree.

HBguy

Anyone who would assume a compressor is bad as a part of a diagnostic on an auto hvac doesnt know what they're doing. Like i always say, never assume a mechanic is a technician and never call a technician a mechanic. That, and f u ck parts changers.

HBguy

Thats funny, you dont sound like you've worked on hvacr components of every tonnage imaginable, including industrial refrigeration, vfds, chillers, boilers, and cooling cowers for skyscrapers....oh wait, thats me! Gove me your theories again? Teach me something. A-hole. Im trying to help people with factsbased on understanding and experience, not typical internet forum guesses from googling.

stgry1

Wow...I'm very impressed with you 'internet credentials'. Unfortunately, no one cares because of how you display yourself and act like a giant wienie. Have a great day!

LILBENZ230

You need to lose the attitude.

A 2009 C300 in our family just had this same issue. A test by Star DAS showed all the components, including the blend doors, were fine. As was refrigerant level. A Mercedes-Benz (& Porsche) master tech advised it was compressor failure. He owns an independent shop and is not by any stretch of the imagination a "part swapper". He has been our trusted mechanic since 1999, when he moved to the states after being educated in Germany, and has repaired many things that dealers would have just replaced. These compressors have no clutch, they are engaged 100% of the time.

Regardless of what you think - and regardless of what you know, as a matter of fact - you will not get far on this forum with this type of response to other members.

amoffitt

Ive been driving the car a bit the past few days and the issue has not come back. It seems to be working pretty well without any issue. I will keep monitoring it and see what happens.

NZ-Merc

Hi,
I recharged my A/C my self and for the following few weeks afterward was having intermittent problems when it was a hot day and I returned to the car after it was parked up the a/c would only pump out hot air.

Just so happened I had the A/C gauges on it checking the pressures and stopped for lunch upon returning to commence work I had the same problem.

The high gauge was reading something like 350-400 psi and I felt the pipe returning from the cabin it was warm not cold like it should be.

Bearing in mind I am no expert on Mercedes or the electrical system:
The car interior and outside air temp was high,
The compressor controller (or what ever it uses) sensed this and sent the compressor vanes to maximum supply.
Car parked with no air flow through the condenser pressure raised quickly.
The max out put of the compressor was to high for the tx valve to process all at once so no cooling happened.
Turned the car off to cool down.

What I did to fix my Merc A/C.
Lowered the pressure by letting some gas out not a lot, since then I have not had the problem again and that was 6 months ago.

My conclusion was this.
Slightly to much refrigerant in the system caused by me filling without scales.

stgry1

NZ Merc, yes you are correct. High pressures or overcharging the system will certainly cause a "no cold" situation as the system will shut down to protect itself. There is a 'high-pressure safety switch' that most systems have for just this scenario. I'm glad you figured it out.

Rakaat

Could you possibly post a video, or visual instructions on what you did to solve the issue?

amoffitt

Hey guys,

I tried to use the A/C today and it did not blow any cold air even with the engine rev to 2K trick. I read over the thread again and is it normal for the pressure to possibly rise by itself into an area where it would be too much to cool my car?

HBguy

you are over simplifying a complex system. This isnt like the coolant in a car. "Is it normal..." thats relevant to charge. Anyone who doesnt measure refrigerants and instead measures resulting pressures doesnt really know whats going on. You can put a band aid on a car oe you can fix it right. Pressure does not stay constant and varies on many factors.

If youre asking if the pressure can be too high to cool it, then yes. Absolutely. If you charge by pressure, you better be looking at both sides and know what the differential should be and what the cut ins and outs are set at. Thats just the basics. Like i said, the fact that gases are sold in parts stores doesnt mean that the average joe can do it. The average technician cant precisely charge a system, let alone an experienced mechanic.

amoffitt

Yes, I understand that if Freon levels are too high then the car will not cool. I might have not written out my question correctly. My question is "is it normal for the pressure to possibly rise by itself into an area where it would be too much to cool my car without the anyone having made adjustments to the Freon levels. The car has never had any HVAC work done to it. My thoughts is no that they cannot rise by themselves but only if extra Freon is added to the system.