jumpman726

I have a 2012 E class. I haven't used the AC in the car for maybe 4 months. It got warm yesterday so I tried to turn the AC on, but nothing happened. The AC light just blinked a few times and went off. Owner's manual says this means there is a malfunction and to take it to the dealer/shop.

I'm hoping it's just low on refrigerant, but how can I diagnose it myself without taking it to a shop? I was thinking about buying an OBDII scanner from Walmart for $20 to see if any error codes pop up.

*SCROLL DOWN TO SEE THE SOLUTION

mj_39

I just had this issue happen to me. Dealer told me the first thing they check is the refrigerant level. Mine was low, recharged and everything is now working fine. They also stated they checked for leaks but found none... I'm still confused as to how the refrigerant level can drop without a leak.

jumpman726

I just watched a YouTube video of a mechanic who said it's normal to lose a little bit of refrigerant over time because of the compressor needing to lubricate itself. He said if you need to add refrigerant every 3-5 years it's no big deal, but if you have to add it every month then you have a leak somewhere.

I don't have the AC gauges or a vacuum to diagnose the problem myself, so it looks like I'll have to schedule an appointment with my indy shop.

thefisch

I kept the gauges from a home self-fill kit that I got from Walmart and have used those to check pressure on multiple cars just to be sure. You might be able to borrow gauges from a local auto parts store. However, IIRC you need to have the compressor running to get an accurate pressure reading. So if you system isn't coming on, then checking the pressure using one of those little kits may not be possible.

Might be best to leave to the 'experts'.

jumpman726

Thanks. I think I fixed it. I watched a bunch of YouTube videos and figured the likely reason for the AC malfunction was not enough refrigerant. Mercedes has a built-in safety feature to prevent the compressor from overheating. That's why when the refrigerant is low it won't let you turn the compressor on.

I bought a can of A/C PRO refrigerant from Walmart for $35. It said if your compressor isn't running you need to first add some refrigerant while the engine is off. I did that, and then turned on my car to see if the AC would work and it did!

I left the AC on and kept adding more refrigerant based on the instructions until it was filled to the proper specs on the gauge. It's only been a few hours, but everything seems to be working fine. We'll see. Here are a couple of helpful videos in case anybody runs into the same problem.

blegthbloo

Ya know... I might actually need to do this on my Subaru... A/C cut out on me while sitting in stopped traffic the other day... works when I'm moving though... takes awhile to get cold, but it gets there eventually. But by then I'm already where I need to be lol

Lumi

roboworks4u

Unrelated but related. My 2013 E550 Cab AC button was blinking 3 times and then blowing warm air. I just added some Freon and now it's butter - cold.

Feuerdrachen

Currently trying to do this now with A/C Pro. Whenever I hook in the gauge goes straight to red indicating that the compressor isn't on. How were you able to get the A/C compressor going to add refrigerant in?

CaliBenzDriver

This might sound simple to some... but if you need freon the fix is not to add a can every month.

Find your leak with a can of freon with UV dye !

Once your A/C system is done loosing most of it's vaporized PAG Oil... the next item is the compressor shooting junk througout the entire system.
That is a A to Z renewal at the busy HVAC specialist.

Get wise about leaks.
🙂

fc3

Umm. You really can't adjust the charge of an R143a system solely by measuring evaporator pressure. You can sort-of, kind-of estimate the correct charge by measuring subcooling and superheat, but that doesn't really work because Mercedes doesn't provide specs and those methods are wonky because of R143a. Or so I've read. I am 609 certified, but not an expert. Please note that Mercedes recommends adding 20 CCs of refrigerant oil when a leak is found and fixed. Note also that additional refrigerant needs to be added when certain components are replaced.

CaliBenzDriver

It's all right to top off a system that is still pressurized... BUT you really don't want to refill a flat system without pumping down all air and moisture traces.
​​​​​
For DIY'ers the question is how many cans?
(1 big one or 3 small ones based on existing load)

A/C works by pressure difference so it's better to be under charged than over charged because it's easier for the compressor to create a low pressure with an undercharged system than with an overcharged one, right?

Subcooling and superheat are a really fascinating science to dial-in optimal charge. Tuning HVAC systems is an expert art skill. 🤗

fc3

There's a label under the hood that shows the total charge amount by weight, but this is for charging an evacuated system. I would not add more than a fraction, certainly more than half of the full charge to top off the system. More than half, and I would think that the system needed qualified attention to address a leak. Keep in mind that leaks tend to allow refrigerant oil as well as refrigerant to escape. One can get away without adding oil once or twice when topping off a minor leak, but other than that, I'd want to add the Mercedes recommended 20cc of oil. Oil starvation is an ugly thing.

Yes, you're correct about over vs. undercharged. However, overcharged systems run a few risks such as compressor loading, backing up liquid refrigerant into the condenser, and excessively high head pressures. While topping off, I would not want to exceed head pressure of 200-225 psi and those would be for a very hot (90º+) day.

Not a fan of R134a recharge kits that are not pure R134a because you have no idea what the proprietary additives might be. Harmful? Helpful? If they're good, why doesn't Mercedes use them and recommend them? The one other thing that bothers me is that the MSDS lists phosphoric acid. Is that included as a component? Why? It's generally regarded that acid in the refrigeration system is a Bad Thing. I never add anything to any A/C system other than the specified refrigerant, the spec oil, and, if necessary, the correct dye. Anything else, IMHO, is asking for trouble down the road.

codebreaker2056

I had this same problem but mine was not a case of low refrigerant levels. The A/C light blinks 3 times then went off, the car isn’t cooling.
The problem immediately disappeared after I changed the condenser switch.

Rickman30

I know this is an old thread, but, the use of stop leak will damage your A/C system, and most shops have a tool called an Identifier to detect flammable freon and stop leak. Why, you may ask. Because stop leak clogs the condenser and switches, as well as A/C recovery machines, causing thousands in damage to the machine. The first machine I witnessed it looked like green slime oosing out of the lines when replacing filter, then machine starts taking longer to operate. That machine was replaced because cost to repair was more than a new machine. You can also use a temp probe to find the clogged sections of a condenser from stop leak quite easily. And yes, auto parts everywhere sells it to DIYer, because the only thing a shop can do for you is to replace everything, try to flush the lines out or replace those too. I just refused to work on them. I kept the old machine as a reminder.

ipanaete91

I'm looking to find where this sensor is located?
how hard is to replace it?

thanks
ion