AC Recharge - 300D - PeachParts Mercedes-Benz Forum

littlerobot · #1 06-11-2009, 01:11 PM

I've just replaced all the diaphragms in the vacuum actuators under the dash, so now my climate control buttons open and close the proper vents. The car (300d) sat in my garage for a year without being regularly driven. The AC worked great before it sat. Now the air isn't cold. My instinct is to take it to a garage for a vac and charge, but that is over 100 dollars, while the canned stuff at the auto supply is 20 dollars. My question is, If I get the 100 dollar vac and charge and it doesn't work (because of a leak or who knows?) then I've wasted 100 dollars. If I get the can and it doesn't work, I'm only out 20 dollars. However, if the AC does get colder, then I can be sure the system works and then take it in for a vac and charge. Is this the right logic and the best way to proceed?

daw_two · #2 06-11-2009, 01:46 PM

If it worked last year and does not now......chances are that you have a leak. You probably are NOT going to find and repair and get a refill of refrigerent for $100. Now, the leak may be small enough that if you get a vac and refill......you might still have cool air come this September.

winmutt · #3 06-11-2009, 01:47 PM

You start by updating your cp or sig and including what year 300d you have. You cannot mix R12 and R134a, so if you have R12 in the system it needs to be vaced before you can put R134a in. The easiest way to determine if its low pressure is to short the two wires on the dryer, this is the low pressure switch. With those two wires shorted and the AC on the AC clutch should engage. If it doesnt you need more coolant. If you have R134a then its time to put some in and add some leak detector. If its R12 then vac it and .... so many options.

littlerobot · #4 06-11-2009, 04:04 PM

Good Point - It's a 1984 300D. Now for a nube question: I know where the drier is, and I see the wires you've discussed, so do I short them by connecting them together?

Also - the compressor fan never seems to come on? -The plastic fan in front of the radiator. Does this come on intermittently? I left the car running with the air on full-blast and it did not come on.

littlerobot · #5 06-11-2009, 04:08 PM

Okay, so to finish my thought....Should my course of action be to have the system vacuumed and charged, and have them put leak detector in while they are at it? I don't have the equipment to do this myself, so the shop down the street will have to do it for me. Also, Daw_Two recommended replacing the drier at the same time. Is this the best course of action in which to proceed?

winmutt · #6 06-11-2009, 04:26 PM

You should replace the drier when evacuating the system.The problem is that the system is not designed for R12 and for the most part all the R134 conversions just lack the cooling of the R12. I would not put R12 in a known leaky system....

With the AC on do you hear the clutch engage? If not then touch those wires together and see if it engages.

littlerobot · #7 06-11-2009, 05:08 PM

I took a pic of the drier, since it has two sets of blue wires. Which two do I touch together:

or these two:

And, should I actually start the car, or just turn the key until the blower motor engages. Will the clutch sound be noticeable?

Thanks!

rscurtis · #8 06-11-2009, 05:17 PM

Connecting the two wires in the first picture will operate the compressor- the two wires in the second picture will actuate the fan in front of the radiator.

littlerobot · #9 06-11-2009, 05:37 PM

So the fan in front of the radiator works. It's a no go on the compressor. Time to add refrigerant? Where should refrigerant be added? I believe the system has been converted to r134, but no way to be sure. It was just a hunch that since the AC system was rehabbed by the previous owners a few years a go it would have been converted. A Vac and Charge up the street is over 100 bucks. Should I get the vac and charge, or the 20$ can at the part supply place and see if it gets any cooler?

winmutt · #10 06-11-2009, 05:59 PM

I'd get the $9 can and see if it leaks. If it leaks then fix the leaks then do vac and charge. The problem is that mixing them (oils or refrigerant) is corrosive and will kill your compressor etc.

snookwhaler · #11 06-11-2009, 06:14 PM

I just went through all of this today. The only difference is that my compressor was coming on and the A/C was barely cooling. When it is 90+ out you could not tell it was on at all.

1 can of R12 later the A/C blows 39 degrees out the vent on low speed, 42 in auto. and medium speed and 45 on high speed. Sitting and idling in traffic or with the car just sitting there I'm getting 50 to 55 out the vents. This is in humid 93-94 degree weather.

Be sure to check your condenser coil. I actually removed my Aux. fan and spent a good hour straightening the fins on the condenser. Then I hit the condenser, radiator and oil cooler with some soap and a high pressure hose. I think this helped me too.

Be sure you know what is in the system before you charge it. Don't just assume what refrigerant is in there or you will screw things up. If it was actually converted, there should be a sticker somewhere stating that it was in fact converted.

littlerobot · #12 06-11-2009, 06:33 PM

Since I can find no sticker, I have no choice but to assume the best (the only sticker on the compressor was "Delphi" - the brand name) choice of action is the Vac and charge at the mechanic - at least that way I'll know what is in there, even if it all leaks out!

On another topic Winmutt, where did you get those rims for the grey Merc in your photo?

Thanks so much for the help everyone!

winmutt · #13 06-11-2009, 06:33 PM

Good call. If it was converted it would have R134 connectors. I would not put R134 in a system with R12. When you short the low pressure switch see if you see bubbles in the site glass on the switch. No bubbles no ref. Some bubbles and you got something left in there.

johninva · #14 06-11-2009, 10:50 PM

It may very well be myself.

Quote:

Originally Posted by winmutt

You start by updating your cp or sig and including what year 300d you have. You cannot mix R12 and R134a, so if you have R12 in the system it needs to be vaced before you can put R134a in. The easiest way to determine if its low pressure is to short the two wires on the dryer, this is the low pressure switch. With those two wires shorted and the AC on the AC clutch should engage. If it doesnt you need more coolant. If you have R134a then its time to put some in and add some leak detector. If its R12 then vac it and .... so many options.

If the compressor isn't engaging & you jump the low pressure switch, and it still doesn't engage wouldn't that mean that there is something else wrong besides low refrigerant pressure ?

Quote:

Originally Posted by littlerobot

So the fan in front of the radiator works. It's a no go on the compressor. Time to add refrigerant? Where should refrigerant be added? I believe the system has been converted to r134, but no way to be sure. It was just a hunch that since the AC system was rehabbed by the previous owners a few years a go it would have been converted. A Vac and Charge up the street is over 100 bucks. Should I get the vac and charge, or the 20$ can at the part supply place and see if it gets any cooler?

If im correct you go some other stuff to sort out before you start adding any refrigerant.