Hi,
Never had prblems with a/c system untill today, I used the GTS as daily drive but high temperatures yet in early morning forced me to turn on a/c.

air from vents is not hot, but is not helping me to cool down cabin space, at a guess I would say it is blowing air at 15 C degrees .

comperssor is on and seems to cut out sometimes, from drier glass I see Always bubbles when the compressor is on.A rechrge is due probably after 4 years.
Looking at the drier I noticed that the red plug , for the recharge system, is leaking a drop of something like oil (or dirty moisture?)...it looks green-ish with a lot of microbubbles .
maybe my system is leaking from recharge plug?How common is this?

I know that PO changed evaporator, vacuum valves and some vacuum hoses inside , heater valve, and so on,....then recharged system 2 months before I purchased the car ....the shop searched also for leaks , but everything was ok .I know the shop and know guys working there, they are meticolous and the PO kept the maintainance of the car fastidiously (apart from body, he was not eagle-eyed so parking manouvres were not 100% trouble free).

reminding that evap and all the internal a/c part were repaired , and that system worked really well till mid august.... can that leak make the system not efficient?

Sorry as usual for my Language , when I talk technical I notice myself that I am not brilliant and need to learn more.

 

Hola de Espña,

the refrigerant in the system is probably low, but still good enough to keep the compressor going.
I think your issue is a bad heater valve. Remove the air filter box and check the operation. I replaced mine yesterday after 10 years of service with no issues. If you valve does not close, most likely your vacuum diaphragm is bad.

Temporary fix. Zip tie the valve manually to the closed position.
http://members.rennlist.com/v1uhoh/hotwater.htm
http://members.rennlist.com/v1uhoh/summer.htm

Real fix. Buy a new valve from your local Mercedes Benz dealer (MA000 830 57 84). Make sure you also replace the short hose from the cylinder head to the valve. This one is only available from Porsche (928 574 567 03)

 

heater valve is working right, no vacuum leaks....at the evaporator: behind central vents the air temp is the same as the outside temp minus 2 degree. evap is slightly cold. I think I have to search for new leaks starting from the recharge valve on the drier /valve body.....boring..... and today I just ordered 2 radiator tanks to fix coolant radiator leaks....I hope it's not the beginning but the end of leaks....mmh....

 

you say you see bubbles coming from the recharge port. This is a schrader valve like a tire valve stem. This should not be leaking, this is a leak. But maybe there are others. You can look over the whole system for any moisture at all the joints, any moisture is a leak. it should all be dry. But maybe this is leftover from old repair. So clean every leak and see if it reappears. Also you see constant bubbles in the sight glass. If it is fully charged there is hardly ever a few bubbles, if it is low charge there is almost constant bubbles

 

You mentioned a the oil substance had a greenish tinge...that sounds like they put some dye in the system. This should make it easier to see if there are other leaks.

 

My understanding is that bubbles in the viewing port means your freon is low, which would match the performance problem you are having. A recharge is quick and easy on wont hurt anything. If you still have enough that the compressor sometimes runs after 4 years I would not worry about finding the leak. You can do a recharge yourself but it is easy to add too much and then it wont work well either.

 

After I replaced a cracked expansion valve, I still had a slow refrigerant leak.

It took about 3 months for the R134 to leak down enough that the compressor wouldn't kick on.

Finally found that one Shrader valve was a bit faulty. After replacing both, the system has been blowing cold since April.

Thankfully it wasn't the evaporator that one "AC expert" swore needed to be replaced.

Sometimes it is the simplest solution.

 

A significant issue with a/c systems is that all too often owners do not know that if the a/c system is not usetd regularly then the seal faces dry out and start leaking a small trickle of gas. It may not be much but as it is continuous over time the amount of gas depletes. Thus you should run the a/c system briefly even during winter time or cooler periods when there may be a tendency not to run the a/c at all.

The situation tends to correct itself once operation is resumed but add such losses to the regular losses the system invariably sees and sooner or later the pressure switch does not kick in and no a/c.

If you have held charge for 4 years then I reckon your system is not doing bad at all.

Ciao

Fred

 

looking at the recharge port, it is not a tyre-type valve after you remove the red cap, looks more a automatic connetion for compressed air hoses, with some "block-air" system that close the system once you remove the recharge hose....

 

It;s still there, it unscrews inside that fitting.

 

The valves inside the connectors are not intended to be the final seal - the screw-on caps do that. The valves shouldn't leak, but it is not a disaster if they do - if the screw-on caps are there and functional.

 

I've rebuilt that system from end to end. If your system is all original the o rings they might have a slight leak. I replaced every one. The other common leak area is the flexible high side line that is on the passenger side behind the ignition box. When I first rebuilt my system that blew. So removing all the o rings and flush the entire system properly. Even removing the compressor and flushing it too is a good idea. Replace the oil in the system in the compressor and when all the system is replaced refill properly. I would replace the shrader valves in the ports just in case. I rebuilt my system and run R134 and have had zero problems since. I run an 80% charge the trick to properly filling is a complete vacuum of the system for about 30 minutes. Then using a scale I weigh out the exact charge into the high side first with the engine off. What ever doesn't go in the high side I finish to the low side. Then I close the valve to the full tank and open both valves to equalize low and high before I start the car. Ok the end my system shoots ice cold air in 115 degree weather

 

inside of the car was pulled that time when evaporator leaked badly.then PO asked to convert system to r134.
when Iwill recharge thesystem I will change, frst of all,valves....
Then I will inspect the system with some fluo gas to detect leaks elswhere....

finger crossed ....

 

So, when the car was converted to R134 were the hoses converted to barrier hoses? If not I understand the old hoses are a bit porous to R134 and will leak down over time...

 

Remember that when refrigerant leaks it takes oil with it. If you recharge enough without adding oil you'll eventually seize the compressor. This is especially important on r134a since that $h1+ leaks so quickly no matter what you do (yes, even from the factory.) 4 years out of a reasonably well-sealed system is about what I would expect from r134a.