I have a 2012 E220 CDI

The AC has stopped cooling, and before this happened the AC was making a hissing sound which went away when the cooling stopped

Also when this problem started only the right side vents were cooling and eventually stopped altogether

My mechanic has done a pressure test and found a leak and is advising me to check the cooling coil

Doing this means opening the entire dashboard to get to the part. So my question are…

1- Is there any other potential area that the leak could be coming from?

2- What are potential future issues I could face if the entire steering and dash sections are dismantled and put back together (it’s an old car)?

3- Can live with the leak if it’s not too bad and top up the refrigerant every few months?

4- What is a bad pressure leak in terms PSI readings and what is the reading usually if it is from the cooling coil?

Eagerly awaiting thoughts and thanks in advance

 

Sorry to read you went to a crazy place.

Absolutely no need to remove dashboard to figure the leak is indeed somewhere else.


Do preliminary testing for refrigerant leak to find it.

This forum has great ppl who can help you pin point your leak :

• Shrader valve,
• pressure switch,
• condenser coil,
• compressor,
• TXV,
• ...
• then Evap coil.

> Both Extremes are bad:
-- Changing everything or changing one part only is the wrong way to stay behind the wheel with these cars.

-- The best deal is to drop all maintenance parts such as: P-switch + S-valves (+ ?coil?) + dryer while circuit is depressurized.

🤞

 

Question to you no 1 :
Your mechanic pressure tested the HVAC system using what ? Shop air or dry nitrogen ?
If shop air, SLAP him and walk away and vacuum your system down to under 500 microns ASAP using service of a true HVAC special shop.
Regular air is wet and that will cause your compressor PAG oil to turn to acid and black death will soon follow.


FACT 1
The moment you loose R134A in your HVAC system, your compressor oil will be stuck at the EVAP because the oil need refrigerant as lubricant carrier.
Compressor Black Death will soon come your way too.

If you ever get unlucky and had compressor failure, you can not clean the damage debris, not with our modern HVAC system having micro channels so small.
You will need to replace all of your HVAC components Compressor, EVAP+TXV, Condenser and all hoses & hose with IHX. Basically 100% all new, if you want it to last 10+ years.


FACT 2
No such thing as measuring refrigerant level using pressure. Even at 20% fill, the pressure will register as normal when measured static engine off.
This is the nature of refrigerant which is at its saturation temperature it is both gas and in liquid form. One must weight by grams and not by pressure, period.


FACT 3
A proper HVAC shop has refrigerant sniffer ( not cheap ) and they can detect a big leak where nitrogen pressure testing at say 200 PSI shows a leak.
No need UV dye if the leak is detectable using pressure.



Where can Leak points be :

AA. Compressor has input and output port. Both uses O-ring at its hose ends. 2 locations.
See all o-rings in blue circle in image below.

BB. Condenser has input and output port. Both also uses O-ring. 2 locations.

CC. Depending on model year, your HVAC may have the IHX, Internal Heat Exchanger pipe system, that means another leak point from extra o-rings. 2 o-rings

DD. Suction or Low pressure hose and High pressure hose has schrader valve each, they do leak when they aged . 2 locations.
Item 5 in green in below parts image

EE. Refrigerant pressure sensor, its o-ring can fail and leak. Item 6 in green in below parts image

FF. The TXV valve attached to the evaporator can leak from its hoses o-rings. The TXV itself uses 2 o-rings to mate the EVAP alu pipes.



I am using my car as example, yours maybe different a bit :




..





GG. Condenser aluminum metal ( core ) can leak from stone impact, as condenser is the very first layer in a car radiator system.

HH. EVAP aluminum metal ( core ) can leak too from corrossion, if your EVAP is never cleaned properly and harbor dirt and whatnot and you live near the sea aka salty air. Evap exterior is always wet you see.


Seek a true HVAC professional shop please.
This is not a DIY job.

Pray the leak is not at your EVAP, because I will cry too when dashboard complete tear down must be done.
PREVENTION-MAINTENANCE can go a long way.

Speaking of PREVENTION-MAINTENANCE, that is a long topic for some other days.

Good luck.....

 

Firstly thanks so much for this knowledge, I can question my mechanic with some intelligence

A few queries before I speak to him…

1- is the evap and Cooling coil the same thing and if not are they located behind the dash

2- my mechanic has informed me that he has checked the following components and found no leaks …

AA. Compressor has input and output port. Both uses O-ring at its hose ends. 2 locations.
See all o-rings in blue circle in image below.

BB. Condenser has input and output port. Both also uses O-ring. 2 locations.

CC. Depending on model year, your HVAC may have the IHX, Internal Heat Exchanger pipe system, that means another leak point from extra o-rings. 2 o-rings

DD. Suction or Low pressure hose and High pressure hose has schrader valve each, they do leak when they aged . 2 locations.

EE. Refrigerant pressure sensor, its o-ring can fail and leak.

FF. The TXV valve attached to the evaporator can leak from its hoses o-rings. The TXV itself uses 2 o-rings to mate the EVAP alu pipes.

I assumed TXV O-Rings can be checked without removing the dash

2- he has checked the condenser unit near the radiator as well and has found no leaks or issues, is there any other part here that could affect the leak

3- Apart from the cost I am not keen on getting the dash removed and my mechanic has said he can service the compressor motor, refill the gas refrigerant etc and it will work fine for another 3 months… so does it make sense to this every 3 months?

 

If the mechanic cannot find the leak, and assuming he did it correctly, it is very likely the leak is at the "entrance" --> Schrader valves. So, if you take the "let us see what happens route", please change both Schrader valve before applying vacuum, recharge by WEIGHT to the exact amount in the sticker under the hood. Do NOT let the mechanic adjust refrigerant by pressures.

Depends on the MB platform, they do not sell the Schrader valve on their own, but the complete hose --> order it aftermarket. I did so for the ML's valves.

Here is a link when I changed the Schrader valves ( https://mbworld.org/forums/m-class-w...ml#post8702673 )

 

KK212 wrote in blue

1- is the evap and Cooling coil the same thing and if not are they located behind the dash
01. Yes Cooling Coil is Evaporator the COLD one. Condenser is HOT, so we can call it hot coil heheheh.

I assumed TXV O-Rings can be checked without removing the dash
YES
Here is a sample


.
My car is RHD, yours is Left-Hand-Drive.
Remove the plastic tray/cowling of wiper and remove complete wiper system. You can then access the TXV



.




.








...




......




....

Wiper tray or plastic cowling.......




How to remove wiper plastic cowling/tray




.....

KK212 wrote in blue

2- he has checked the condenser unit near the radiator as well and has found no leaks or issues, is there any other part here that could affect the leak
It is not easy to find a leak if by visual only on condenser. The leak could be at the engine (rear) facing side and not bumper (front ) facing side.
There is a filter drier cavity where it has o-ring too. So it can leak from there too. Anything using o-ring, will eventually leak.



..




...
Yes funny name CAPACITOR for Condenser.








...
3- Apart from the cost I am not keen on getting the dash removed and my mechanic has said he can service the compressor motor, refill the gas refrigerant etc and it will work fine for another 3 months… so does it make sense to this every 3 months?

Your R134A fill would be approx 590 grams for a sedan. Must check MB WIS or the sticker at the engine bay.
If you loose more than 25%, that is dangerous for the compressor oil to not be able to tag along the refrigerant to circulate back into the compressor.

There is nothing to service for the compressor, not if it is not DEAD/DAMAGED yet. When damaged, your replaced more than just the compressor if the debris has circulated.
The EVAP need to be clean, hence the paper filter must be replaced maximum per 2 years, depending if you like using OUTSIDE air or
CIRCULATED air. If car is clean inside, and like me always using CIRCULATED air, the filter wont be dirty even in 3 years, but the activated charcoal inside it will be "wet" saturated and cant capture smell well.
In a proper sealed system and very dry to begin with, the compressor oil will last easy 15-20 years, but the shaft seal of a compressor will leak annually 8-12 grams of R134A, more if the engine is not run often.
The compressor oil ( when running ) helps the shaft seal to be wet/lubricated and more gas tight.

Condenser need to be clean at its fins ( exterior ), otherwise the compressor will overheat.

He estimated 3 months it will be OK when charged up again with R134A to proper fill, is simply an estimated guess. 3 months from now he will know how many grams you will loose the R134A and he can make adjustment.
But this is only true if the leak is not getting any bigger and at area where the leak will not make your compressor oil also depleted.

Take a paper towel, access the High Pressure (HP) port, the thin pipe ( liquid pipe ), press a bit on the valve and let it stain your paper towel with compressor oil and R134A. Smell it, that is the smell of R134A and the oil.



If you smell the same in the car interior with HVAC running using CIRCULATED air, you very much likely have EVAP leaking at its core/metal and the R134A smell will be strong.


It smell like a hospital clean room, ether kind of smell.




Use a boroscope and see how dirty is your EVAP.
Sometime leaky EVAP can be seen, as dirt spot....dirt like to stick to the leaky part due to it surely having compressor oil trace.



I hope your mechanic HVAC RRR machine is well maintained and has refrigerant identifier and he has a stand alone micron gauge ( ultra high performance vacuum gauge ) and use it PROPERLY at a proper LOCATION.
Poorly maintained RRR machine and without refrigerant identifier can be a disaster for you, as the same machine collects all the cars refrigerant the workshop work on and
charge back to your car. So if the previous car has contaminated refrigerant, you too get the bad luck.

If his machine is capable of yf1234 new refrigerant and a dual system R134A / yf1234 and is SAE J2843certified, it will come with refrigerant identifier.
Just so you know, all these RRR machine, the vacuuming power is bad, usually 3CFM or at best 6CFM for newer ones. Often single stage vacuum pump.
Hose too long at 6 feet at least, using the same "wet" refrigerant hose for vacuuming and is a small hose.
Their vacuum reading is at the RRR machine, at its manifold, close to the vacuum pump = BULL-Shiet reading and it is not micron gauge but a simple inchHg vacuum gauge at best,
which is useless for true HVAC work.

See, even 1 millibar is too wet, because it is 750 microns.
Even 0.1 inchHg is too wet.




........




..





The car HVAC workshop is a joke. Unless the guy does also commercial units.
See what is the industry/commercial average dryness ( microns ) when doing vacuuming, see Daikin below :

......


Have fun..............

 

Is your A/C hissing sound when you in the car. Hissing and when stop hissing, A/c gone away that mean your A/C leak not small, and gas run out of system.
If you can hear hissing sound in car, that mean your evaporator is leak. And your mechanic is right.