lightfytr

Fellow W212 owners,

Any of you experience a delay with your AC getting cold and notice if you push the accelerator hard it begins to cool?

There are times when I can turn the AC on and it not get cool at all until I take action such as turning the car off and on or slamming the gas pedal momentarily to "engage" the AC.

I recently realized slamming the gas real quick sometimes wakes the system up. BTW this only happens about 1 out of every 10-15 starts.

Mud

Most vehicles delay the a.c. slightly after initial cold engine start and when WOT is engaged. I suggest checking both high and low pressure sides in your system, sort of sounds like possible low refrigerant level or issue with compressor clutch engagement.

lightfytr

Good point Mud, its likely the gas pedal slam engages the compressor clutch when its delayed...

Mud

Maybe helps a bit its my best guess :-)

The typical system uses a pressure switch to also control the compressor. Too high or too low presssure will not allow the clutch to engage. Its usually a 2 connector plug either on the compressor or by the drier (accumulator) somewhere. The contacts in the plug can be jumpered temporarily just to verify if the switch is at fault if the system pressure has been checked and is ok. There is a relay that controls clutch engagement as well but I dont think the relay itself is at fault. Maybe also check all connectors too.

cetialpha5

I believe Mercedes now uses a variable displacement compressor. There's no clutch. It just takes longer for it to kick in. This way you never notice the clutch kicking in. Guess it makes for a smoother ride but takes longer for the a/c to get really cold. There might also be a problem with your system, I'd get it scanned to see if something is off. Mine had a bad temperature sensor in the passenger footwell at one point. Didn't seem to affect me on the driver's side though, but I got it fixed anyway. I have my own little scanner than does MB specific codes, but I'm not sure I'd take it to the dealer and pay their $150-$200 diagnostic charge if it doesn't bother you that much. The scanner cost me a lot less than that.

ItalianJoe1

Correct, it's a clutchless variable compressor. Problems with delayed cooling are often related to the refrigerant control valve (RCV) that actually controls the effective displacement. If you remove it and clean it up it usually makes it function like a new compressor, unfortunately this requires draining/recharging the a/c system so it's not a DIY. The valves are cheap, although not available from the dealership, it only comes with the compressor.

In the VW world, they die all the time, and i've saved people $1000 over a dealer quote for compressor replacement by just changing the valve and getting them back to 100% for very cheap.

Mud

Great info, thanks. I'm still in the stone age sometimes.

mnje350

I have noticed this issue in my 2010 now for a while. After cold startup the ac won’t run until I rev the engine till about 2000 rpm. Then the system operates normally. I wonder if it will get worse. I can easily live with the way it is now.

lightfytr

Mine doesnt really bother me enough to spend money on it. Pushing the gas pedal to get it to work is no biggie. It has sucked once or twice when I turned my car on early to cool off and only to come back with the AC never have engaged. Oh well.

ItalianJoe1

It will eventually stick completely, the valve is a small solenoid that moves back and forth to get the desired flow through the compressor. You revving the car shocks it enough to make it open. If you removed it, cleaned it and covered it with oil, it would probably work like new for another 7 years. They very rarely burn out electrically, they just get contaminated and sticky. Sadly it requires opening the a/c system to do it though, so not a DIY job.

lightfytr

Any idea, if a shop would do it or would most want to just replace the AC?

I've done some pretty serious maintenance and repairs myself. Is it that intense?

cetialpha5

You would probably just have to find an A/C shop that's familiar with it and tell them to do it. That way you just pay for the work and if it doesn't fix it, try again. Normally for A/C work you have to vacuum the refrigerant out, fix the problem and then vacuum the air out and recharge it. Most DIY people don't have that equipment. Some generic shops around here advertise $80-$100 for A/C service which I assume probably means a vacuum and recharge. Probably extra for any parts like seals, valves, compressors etc.

ItalianJoe1

Not difficult at all, but you need to evacuate and then recharge the system, which is above the capability of a home mechanic.

The valve will have to be sourced from a local a/c shop based on your compressor type, the dealer will not have a listing for it, and the a/c shops won't know what compressor is on your car, but if you can tell them the model # on your compressor, they can get you the right valve.

Arrie

Why not a DIY job?

ItalianJoe1

It's literally 4 posts up, did you read? Even the one right before your post where I answered the questions?

It required evac and recharge of the a/c system, which 99.9% of home mechanics cannot do.

Arrie

I still ask you why not DIY?

Recharge is super easy as you can buy the "Freon" which is not Freon. It is the "nature friendly" a134 available for everyone from any auto part store.

Evacuation is simply letting it out. The trick is to pull vacuum in the system to get air out or minimize the air amount in the system before filling it up. For this I use vacuum from my old pick-up truck that has a point after the carburetor butterfly valve but I'm sure there are plenty of low cost vacuum pumps available for this. So again, why not a DIY job?

And 99.9% goes on any job amongst people who buy these cars. People active in this forum are different breed and lots more can do this job than 0.1%.

cetialpha5

Because it's still illegal to just vent refrigerants into the air. You should not advocate it just like copying navigation DVDs.

https://www.epa.gov/section608/stati...g-refrigerants

ItalianJoe1

This is why you should not do it. That's not the right way to treat your a/c system. I don't care about the environment, but you want to avoid moisture in your a/c system for proper life and function of components.

Vacuuming it from your old truck sounds like a really half-*** way to do it lol.

You want to pull complete vacuum (~30in/hg), and maintain it for at least 15 min, I like to go longer if the system has been open for more than a minute or I replaced any major components. This is to boil off the moisture that's in there and remove it. Should always replace the drier when it's opened, as the dessicant only works one time, but in theory if not much moisture gets in, the drier doesn't have to remove it.

I disagree with your .1% assessment, most people with a little logic and basic tools can do brakes, reseal a valve cover, etc. Those are things I would readily consider a DIY. A skilled guy could easily R&R a transmission and do a rear main seal on the ground, not a big deal really. The reason people don't do a/c work themselves is they don't have the tools.

If you want to, buy a proper vacuum pump and a set of manifold gauges. Used right, you can absolutely do it yourself, and do it close to properly. There's no way I know of to recover the existing refrigerant and re-charge with it without a specialized machine, but yes you could always vent and purchase new refrigerant ("Freon" is a brand name, the old stuff was called R12, newer is R134, newest is R1234). At what point the cost balances out with just paying someone to R&R the valve and do it right, depends on how much you value your time and if you purchase cheap/used equipment.

Arrie

Man, all I ask is why not DIY job and you start giving a lecture about how to do it. You explained yourself how to DIY it. The only special tool that is not laying around "everywhere" is the vacuum pump but it should not be too hard to find.

I used my truck intake manifold vacuum as it is quite good at around 22 in/hg. And I seriously doubt the pros pull 30 in vacuum either. Anyway, my A/C on my old Lincoln worked just fine after I fixed it and used that old truck for the vacuum.

ItalianJoe1

I use an actual a/c machine and pull proper vacuum.

If you choose not to do it right, more power to you. Just please, don't recommend people do it the half-*** way, when there is a right way.

Arrie

I have not recommended anything in this post yet. Just questioning your opinion it is not DIY job.

ItalianJoe1

A/C system charging isn't DIY unless you have an A/C machine. Not an opinion, the way it works. If you want to ignore the "right" way to do it, a lot of things are possible.

Sehill

I know this is an old post, but it's still relevant. In the owners manual it says you have to set it to 72 degrees if the outside temp is very hot. If your AC is set on let's say 60 degrees, it will not turn on until that temp is reached. Always set it on 72 degrees before you turn it off and once it gets cold only decrease the temp in very small increments i.e. one degree every few minutes so it can catch up. That's it...you're welcome.