S320 AC problems - Page 2 - PeachParts Mercedes-Benz Forum

Matt L · #1 06-11-2009, 12:42 AM

Quote:

The low pressure fitting is in the front, right next to the ac cooler, isn't it??

NO!!!!! That's the high-side line!

The low fitting is in the line between the evaporator and compressor, in the engine compartment.

You said that your compressor wasn't engaging. That means that even if you do have a duovalve problem, you also have an AC problem.

amosfella · #2 06-11-2009, 12:47 AM

Thanks for the correction on which fitting... I figured the duovalve and A/C problems were separate.... Now, I heard that unplugging the duovalve causes the heat to be at high all the time. Which plug or both??

amosfella · #3 06-12-2009, 03:37 PM

I checked the pressure in the low valve. it read 60 psi, and the compressor started today when I started the car, set all the dials to 'lo', and turned the economy off. Might my ac problem have to do with the outside temp sensor that seems to display on my dash intermittently??
Btw, the gauge was reading about 15 psi before I put it on the car. Dad said it was reading the ambient pressure in the atmosphere.

Matt L · #4 06-12-2009, 08:24 PM

The gauge reads PSIG, or pressure above ambient, so if it read 15 before you hooked it up, it would mean that you really have 45 in the system.

For AC work, only vacuum is ever measured as absolute pressure (in microns of Hg). Otherwise, it's PSIG (G is for "gauge").

45 PSIG is very low unless it was rather cold at the time.

amosfella · #5 06-12-2009, 09:49 PM

it was about 18 C at the time, but I didn't have the car running. I guess I'll have to get a can or 2 of R134a and filler' up....

amosfella · #6 06-13-2009, 02:45 AM

What is the correct pressure for that system on the low side while the car is running?? I can't seem to find that info anywhere.....

Matt L · #7 06-13-2009, 11:46 AM

That information is in the FSM. There is a set of charts, where you look up the values depending on several variables, the biggest of which is the ambient temperature.

But the low-side pressure alone is not enough information to ensure that you have a proper charge. You really need the high-side pressure if you're not doing it right and recharging by weight.

amosfella · #8 06-13-2009, 11:50 AM

Could you post the chart?? I can't seem to find that in any of my stuff. Looks like I'll have to buy the adapter for the high side as well.

Matt L · #9 06-13-2009, 12:42 PM

Actually, I thought I had the cart for that car, but my (paper) manual somehow omits it. It's not even listed in the contents for that section. It has everything but that chart for the 140 through MY1995.

Maybe someone else has a different manual, or even an electronic copy with the chart. There is one in my 210 FSM DVD, for example, but that's a different car.

amosfella · #10 06-13-2009, 03:53 PM

I've looked through alldatadiy. Nothing on pressures, only weights. The only thing it ways is to check the sight glass and fill till there are no more bubbles.....

How hard is it to suck the whole system out, and put r12 or r14 in there.....

Matt L · #11 06-13-2009, 06:58 PM

It's not that it's hard to recover your current refrigerant. The problem is that it requires tools that few DIYers possess.

It is always best to recover and recharge by weight. The FSM for my 210 does give a pressure chart, but it says to use it to confirm proper operation of the refrigeration system if there seem to be problems once you have filled it to specs.

amosfella · #12 06-13-2009, 10:39 PM

I could recover, but I couldn't recharge it by weight. at least not from what I took out. Can one after taking the R134a out of the system, and put in r12??
I might try to fill it with the sight glass system..... might work.....
Should I try to get the stealership to give me a pressure chart??

amosfella · #13 06-14-2009, 12:35 AM

I have a 30 pound can of r12a kicking around. That's why I"m asking about swaping gases....

Matt L · #14 06-14-2009, 11:49 AM

No, do not put any R12 in there if it came with 134a as they use different oils. Sell that to someone with an older car (or keep it around for the future for your own older car). I recently paid $90 for a 30# cylinder of 134a.

amosfella · #15 06-16-2009, 01:22 AM

not R12, it's R12a. Duracool. Here is the link....
http://www.deepfreezeinc.ca/faq.htm
I vacuumed out he system today. I can't get cans of R134a in Canada.
I use it on a bunch of the farm equipment and such for ac refills... and some of the older vehicles... R134 is almost impossible to get here....