In search of MB A/C servicing primer

[brookspw]

This is a request for several pieces of information regarding the testing and charging of the A/C system in our Mercedes, specifically the 1991 190#E 2.6, in my case. I suppose I am mainly asking LarryBible, since I’ve seen him posting concerning these matters the most. However, I know that there are several others with the knowledge and experience in this system and I’d welcome the instruction from anyone.

Preface: I am quite handy mechanically and on my car. I just don’t have much experience working with the A/C system. I did pass and receive my 609 certification and have purchased a manifold gauge. Depending on those readings, I will be purchasing R12 and lubricant/oil. My car has never had an A/C service in its 13 years of service (I bought it 3 years ago). The A/C has worked fine, but its cooling ability has diminished slightly each of the last 3 years. I am told that even a “non-leaking” system can lose and ounce or so of refrigerant each year due to hose porosity, etc., so I may be close to a pound low of R12 from the system capacity of 2.2 lbs.

Questions:

1. What should my high and low side pressures be? I am assuming, of course, that this is with the engine running – but is it with the A/C on or off? I assume, ON.
2. How do I know, depending on the readings, how much R12 will be needed?
3. How much lubricant/oil should be used (ratio) in relation to the R12?
4. Anything else you want / need to tell me.

Thank you

[jbaj007]

This is a good primer: http://www.ackits.com/index.cfm?fuseaction=Manual

[brookspw]

Ok, let me rephrase: "I'm looking for a member here to provide me with this information."

I meant primer as in instruction, not a printed manual. Thanks, though.

As Golden Rule suggested that is a very good book to use to learn the fundamentals and concepts involved. It is very worthwhile to keep handy as it shows different guage readings and symptoms to use for determining the nature of your problem while troubleshooting with your guages.

To start with hook up your guages and see what your static readings are. If they are in the area of 80 pounds or so, then your clutch should kick in. If it will then go ahead and start up the ac full blast and see what the readings are after running five minutes to stabilize the system to get meaningful readings.

At that point, the book would be VERY useful in deciphering what you're guages have indicated to you. Since you don't have the book, post your readings and other symptoms here and we'll do our best to help you troubleshoot from long distance.

Good luck,

[brookspw]

Ok, I'll get the book. Does it give me any Mercedes related info or just general?

Will it go into the other questions I asked, such as how much r12 to add, how much oil per r12, etc.?

Found a great Manifold Gauge at Harbor Freight for $29.95.

Thanks

[dmorrison]

The Harbor Freight guages are not the best, BUT, will do the job. I have 2 sets. One R12 the other R134a. Get the book. It will help with guage diagnosis and information. I do not know if the book has info on your car. But my book does.
Haynes Techbook, Automotive Heating and air Conditioning

1991 190#E 2.6

Low side guage 24-34 psi
High side guage 230-275 psi
5.00 Oz of oil
2.2 Lbs of freon.

Now this is for R12. If you convert your system, make sure you do it right, Oring, flush etc, The amounts for R134a freon will change.

Dave

[brookspw]

Originally posted by dmorrison

1991 190#E 2.6

Low side guage 24-34 psi
High side guage 230-275 psi
5.00 Oz of oil
2.2 Lbs of freon.

Now this is for R12. If you convert your system, make sure you do it right, Oring, flush etc, The amounts for R134a freon will change.

Dave

Had only 7-8 lbs of pressure in the low side. It did take the 12 oz can of r12, but it was VERY slow. It took 15 minutes or so for it to suck it in.

At the moment, I haven't been able to check the high side pressure. I certainly do not think it is high. 2 reasons: 1) My compressor continues to run, it would shut off with high pressure -- right? 2) My high side hose should be hot, or at least warm, due to the pressure (with the low side cold) but it is just barely more than ambient temp.

Any comment on why it took so long to suck down the can of r12?

Also, my sight glass was VERY cloudy -- looked like milky bubbles. It is only somewhat less bubbly now. Probably needs part or all of another can of r12. I'll wait on testing both pressures before I do that, though.

[brookspw]

Oh, and by the way...

The air is considerably cooler than it was previously. Not yet where it needs to be, but quite a bit better than before.

My low side pressure now is about 20, so I will need more freon. Just want to check my high side first.

On putting the freon in -- years ago when I used to put a can in my truck every few months, it seemed to suck it down like a wino having the DTs.

Any thought as to why mine was so slow?

Sometimes a system will draw a can of R12 pretty fast, other times it is necessary to put the can down into a bucket of luke warm water to get the refrigerant to boil out of the can.

Good luck,

[brookspw]

Originally posted by LarryBible
Sometimes a system will draw a can of R12 pretty fast, other times it is necessary to put the can down into a bucket of luke warm water to get the refrigerant to boil out of the can.

Good luck,

Ah, good idea. Necessity is indeed the mother of invention.

[pmizell]

What book does that broken link refer to?

I recently did some A/C work and it's blowing adequately cold (50F on a 93F day) but me being the perfectionist, I know I can get it colder.

After rebuilding my compressor, I added 8oz of oil and I'm thinking that may have been too much. (seems a bit inefficient)

Cheers

[jbaj007]

Link repaired (at least for now).

[fiero4819]

I recharged my AC and it worked for awhile. All of a sudden it seemed to stop working. When I check the compressor, it cycles on and off about every ten seconds. I also noticed that when I'm at highway speeds, I am getting cold air out of the vents - just not enough since the blower doesn't turn. Nor does it turn when the heat is turned up. Does this sound more like a vacuum problem or a blower problem? In either case, what's the best way to proceed?

Thanks.

pmizell,

I've been exactly in your position. Refer to my thread "At Least the Evaporator Isn't Leaking." It is easy to check the vac pods with a mity vac or other vac source by removing the glove box and removing each line from the manifold. Likely the Fresh Air/Recirc pods are bad. If they are good, rig up a test led and check the diagnostic connector near the battery to see if there are any codes. I think I had a thread previous to this one that had some links to all the info you need.

fiero4819,

Is this problem on a Pontiac Fiero? What kind of car are you asking this question about?

Thanks,

[fiero4819]

I have quite a number of cars... it's just that the Fiero is one of my early acquisitions and I have used that handle on all the forums ever since.

In this case, the car is a 1991 MB 190e 2.6l.

I'll check the diaphragms this weekend but would that also explain the blower not spinning? I've heard the bushings on these blowers is prone to siezing and my best bet will be to figure on replacing it.

Thanks