So i'm sure i have a slow leak somewhere and was going to pull the vacuum after identifying the low pressure connector (near the firewall) and high pressure connector (in front of radiator by electric fan).
Now the label on the fuse box says the following as per the image.

So the truck takes both 134a (1.65 lbs) and oil (.07 lbs). So i got a 134a+oil recharge can, which is 18 oz. However, it does not say how much is oil and how much is 134a. If I pull the vacuum, i'll empty both 134a and oil. So, when i go to recharge, do I use almost 2 of these canisters? Or, should i buy pure 134a and oil (don't know where to get that from) to put into the system? Also, does the oil go into the same low pressure port?

The pressure, according to a PDF found on the net, is 36 PSI.

Thanks,

Label on fuse box in engine bay

Maneesh

 

Maneesh,

Some nfo for you to read and digest (for reading pleasure only)
https://www.techchoiceparts.com/refr.../mercedes-benz

For viewing pleasure only.

Now you have a tidbit of nfo to get a very basic understanding of AC.
As many veteran members have said, "if you do not have full understanding of AC, the mechanics, the electrical that makes AC work properly, or the proper equipment (manifold gauge, vacuum pump, recovery tank, etc), know the components of the AC system that should also be checked and/or replaced, then, respectfully, you are committing suicide.
You have not even brought dye into your equation.

 

khomer2, thanks for your reply.

I got a set of manifold gauges - looking to connect them this afternoon.
Multis-system OBD reader on order, recommended by Major Dundee.

Now - will check the pressure with the guages. Thanks to the link to the you sent, I know that this takes PAG-46 oil.
The quantities are listed on the fuse box so I have that. (26.4 Oz R134a, 1.12 Oz PAG 46 oil)
The normal pressures are provided by some PDF that someone else has linked, so i can check low/high pressures.

Providing that the code reader does not find any faults in systems, my choices are:

1. Pull a vacuum. Use a 3 Oz container that has 1. Oz PAG 46 oil, 1 Oz R134A and 1 Oz additives/sealers, and 24 Oz R134A, for a total of 27 Oz of fluid. ( a little less than what is recommended.)

Or 2, Not pull a vacuum, "top off" refrigerant with dye, and find the leak, and address the leak. And then based on that - fix the leak and do option #1.

Any suggestions or other thoughts.

Thanks,
Maneesh

 

An update - AC fixed some what:

so, i connected the gauges and saw that HI and LOW sides were low. this is a sign that you need refrigerant. So i vacuumed the system to -30 mmHg, could not get it lower than that.

Got two cans of 12 oz 134a, and put in 1.75 cans. The AC blows cold, not as cold as it used to be but it blows cold.

Now yesterday, it would not blow cold air when I went to get some food. So i thought perhaps there is a leak and I lost the refrigerant. But after pickup up the food, the AC started blowing cold air, nice and cold. Could not explain this. Last night again, a few hours later, it was blowing cold air.

Now today, no cold air on a trip to ATM. After starting the car, there is no cold air either. So not sure why there is intermittent AC. There are no wierd noises either.

I am also trying to sort out another issue where even though i have the vent dial to the "3 vents" i get air by the windshield. If i turn the dial to the "top" I get air form the windshild and not the "3 vents." So the dial works and the motor works. But when I have the dial set to "3 vents," it should not be sending air air from the top. any thoughts on fixing this?

Thanks.

 

I'm almost positive that it is a problem with your blend door actuator/motor. They were pretty unreliable in these models. I had the same problem last summer and there was no clicking like this guy's. It was just getting stuck on heat.



I'd check your cabin air filter while you are at it.

 

Cabin air replaced last week after the recharge.

The only reason why I don't think it is the blend motor is because I do get ambient air when NO AC, hot air when i turn all the way to the right. ANd when the AC does work, i get cold air.

I have two problems:
1. AC working intermittently
2. Air not coming out the vents they are supposed to. And I don't think the car is recirculating either when i press the button. in the past, the fan speed used to increase and the noise used to be more when i press the RECIRC, now I don't here it.

 

I mean it's pretty easy to check. Next time it's blowing hot when it should be cold, pull over and pop the hood. Is the AC clutch spinning? Are the pipes around the recharge valve cold? If yes to both of those, the next thing to check is the blend motor.

 

This is NOT how to diagnose a faltering AC system.
Rudimentary comments like this are a waste of time.
AC systems are very complex closed systems. Even watching the plethora of YT videos claiming DIY fixes can cause more confusion that solutions.
If you wish to take advice from members with bare minimal hands-on AC experience here, then take all with a 'grain of salt' and view it only as "for reading or viewing pleasure only"

 

Well - here we are again 2 years later.

No AC this summer.

Based on reading codes (B1204) in the vehicle, the defroster flap motor actuator is not working or the control arm is broken. I'll get to this after the AC fix. Already removed the instrument under panel and it is being glued b/c the cheap plastic is broken. But this explains why I get little air out of the side vents and air from the top/defrost when I don't want it. Hopefully it is not the motor, I just need to buy a new control arm.

Taking advice from Maj Dundee, I replaced the aux water pump in 2021. No biggie.
Maj Dundee suggested that I look at the AAM module board - no circuit board burnt there

So now I pulled a vacuum and it was maintained overnight. I put in R134a (it is going in very slow), but as I put it in, the low side temp goes up to 60-70psi, then aux fans kick in (i guess the compressor is running), and the pressure goes down to 30-40psi. the aux fan runs only for a few seconds, at most 10. then only kick in when the low pressure goes to 60-70psi. It is blowing cool air, but not cold as I expected it. It also takes a long time to take in the freon. I just did not feel like letting the engine idle so i stopped it and will pick it up again tomorrow.

There is a hissing noise when the AC gets turned on, it's been there for 2 years. Not sure if that would be a problem.

Cabin air filter is clean.
need to check the blower motor and clean - i am pretty sure it runs as I can feel the air but will check and clean anyway.
Have not checked the e-box fan. I think there may be an issue with this one
I don't think the blend door motor/actuator is broken b/c I would have had a code for it

So I still have not come to the core of the problem and the saga continues. At least I have a little cold air now.

 

Check your shredder valves first off. quick and easy.

 

I was able to add more refrigerant into the system and it blows nice and cold. Am not sure long this will last.