Basic AC Questions on 87 300D - PeachParts Mercedes-Benz Forum

a2t · #1 05-06-2008, 09:47 AM

Running ES12A on a 1987 300D turbo.

1. What is the system capacity? I have 1 book that says 36 oz, and one that says 48 oz. -- edit, answer is 36 oz.
2. Is it normal for low side to run 60 psi and high side to run 200 psi at idle ?
3. Should compressor cycle on/off on this car? Mine stays on whole time.
4. Any idea what white milky substance in site glass indicates on a 36 oz charge of ES12A ?

Im not getting very good cooling from AC lately. I evac the system to 30 in HG and it held. Recharged --edit -- 18 oz ES12A. Site glass was and still has milky white foam. Gets kind of cold on hwy, blows warm at idle. Any help appreciated.

jkoebel · #2 05-06-2008, 09:56 AM

1-Should be a placard in the engine bay that indicates the charge.
2-What coolant? 134A, seems to be around 20s-30s low/200+ high, so you're off by a fair bit.
3-I think on those Type III climate control systems, the compressor is on full-time, and is not cycled on/off to modulate the temperature.
4-?

bobodaclown · #3 05-06-2008, 10:00 AM

Low side seems high. High side seems low. Could be compressor could be worn. Have you done any work to the system? Did you change the Expansion Valve and Drier?

jcyuhn · #4 05-06-2008, 10:11 AM

The factory charge is 1Kilogram. Of course, that's for R-12. Since you are using a hydrocarbon refrigerant, that information does not apply. My vague recollection is that hyrdrocarbons are much lighter, hence take a much smaller charge. I think that you are very badly overcharged. The low side pressure seems to indicate as much.

I think low high-side pressures are one characteristic of hydrocarbon refrigerants. There used to be an automotive a/c forum with an alternative refrigerants section. Such things were discussed there.

The compressor will cycle, but only if the evap gets cold enough that ice might begin to form. The pushbutton unit has an evap temperature sensor as one of its inputs.

- JimY

bobodaclown · #5 05-06-2008, 10:40 AM

Attached is PDF with temp and pressures for A/C System. Takes the guess work out of it.

jcyuhn · #6 05-06-2008, 12:12 PM

Quote:

Originally Posted by bobodaclown

Attached is PDF with temp and pressures for A/C System. Takes the guess work out of it.

Those are for R-12. Don't apply for otherrefrigerants. R-134a has a similar-ish enough pressure-temperature curve that you can use those same charts. But ES-12a - who knows. Anyone have a chart for it?

- JimY

hitwtom · #7 05-06-2008, 12:25 PM

Here is a good place to start : http://www.aircondition.com/wwwboard/alternative/current/7348.html
after reading this, see if your problem is with the oil. Moisture in the oil will also cause the milkiness.

Cervan · #8 05-25-2008, 10:03 AM

Quote:

Originally Posted by jcyuhn

Those are for R-12. Don't apply for otherrefrigerants. R-134a has a similar-ish enough pressure-temperature curve that you can use those same charts. But ES-12a - who knows. Anyone have a chart for it?

- JimY

uh, i wouldnt ever use an r-12 chart for 134.. 134 is waaay over the pressures of R-12 not even close.. I think you not only overcharged your system but your expansion valve isnt working correctly.

a2t · #9 05-06-2008, 01:17 PM

OK some more details, thanks for replies on here thus far.

Im using ES12A, not R12 or R134a. Ive found in the MB FSM it says refrigerent capacity is 1.1 kg = ~38.8 oz. According to the ES12A cans, (1) 12oz can of ES12A = 18 oz of R12. So I put in exactly 2 cans after the system was completely evacuated and held 30 in Hg, so it should be just a tad under charged by about 2 oz. No way its overcharged.

I just drove it on highway, ambient 85 F and its blowin snowballs at speed. When you sit at idle, it gets as hot or hotter than ambient though. The electric fan cycles on and off, but I only have ever heard 1 speed. I think the pressure switch trips it onto speed 1 over about 200 psi. Maybe there should be a second speed, as air moving over the condensor seems to really improve the vent temps.

The site glass is still milky white, I will look into that more.

jcyuhn · #10 05-06-2008, 03:27 PM

OK, you said 3lbs in the first post, that would definately be overcharged.

The electric fan is triggered on low speed by high side pressure in the a/c system. That's the green (or maybe red) switch on the dryer. High speed on the electric fan is triggered only be engine coolant temp reaching 105C.

This car has a small a/c compressor which is turned rather slowly by the low idle speed of the diesel. It's normal for the a/c to not be as cold at idle.

Do you have a themometer to measure vent temps? Tough to say how well it's performing without objective measure.

I checked the pressure/temp chart and 60PSI is a good target lowside. However, that's what you want it to stabilize at running the engine at 2000RPM. If you're getting that at idle, probably undercharged. May want to add some refrigerant. Using alternative refrigerants is always an inexact science.

- JimY

a2t · #11 05-06-2008, 03:48 PM

Quote:

I checked the pressure/temp chart and 60PSI is a good target lowside. However, that's what you want it to stabilize at running the engine at 2000RPM.

Thanks Jim. Where did you find the pressure/temp charts? I'd love to have a look, seems the best way to understand if the charge/pressure is right.

Those charts spec out the curves at 2k rpm, not idle? I think at 2k rpm mine is running about 20 psi on the suction side.

jcyuhn · #12 05-06-2008, 05:34 PM

Just Googled up "es-12 pressure temperature chart" and got their home page: http://www.befreetech.com/envirosafe.htm It's difficult to read, partly because they screwed up their HTML.

Another option might be to search for other users of hydrocarbon refrigerants and see what is their experience. There used to be an alternative refrigerants discussion at www.aircondition.com, but they appear to have gone PC. There are some old discussions laying about: http://www.aircondition.com/wwwboard/alternative/current/7348.html and http://www.aircondition.com/wwwboard/alternative/index.htm

Hmmm. The 2nd link says hyrdocarbon blends don't cool well at idle. Oh well, give it a read and let us know what you learn.

- JimY

a2t · #13 05-23-2008, 10:30 PM

After I pulled vac to 30 in and recharged, it seems to blow cold when moving.

Someone said I should of recharged under vac, however I did not.

think that would affect cooling? The directions I got from the ES-12A vendor said to never charge under vacuum, so I didnt.

Matt L · #14 05-25-2008, 01:39 PM

It is hard to imagine that you actually want air in the system when using hydrocarbon refrigerants. Air reduces cooling capacity. Yet the vendors of hydrocarbons actually tell you to let air into the system. This seems bizarre.

Why can't you meter the hydrocarbons to avoid overcharging, even if you charge into a vacuum? It's not like you're forced to add an extra can. The amount of hydrocarbons required fill the system with gas will be minimal.

I read of one person who installed ES12 and decided to break the vacuum with propane. This would seem to throw the mix off. Why not just break the vacuum with ES12 and add what only is required?

Can someone who has knowledge of these systems attempt to break what seems to be a conundrum?

a2t · #15 05-25-2008, 09:27 PM

Im only going by directions given from ES12A vendor, not to charge under vac. I pulled 30 in HG, let it sit for about 1 hr, it held pretty close to 30 in HG.

Then shut off pump and let system equalize back to 0, then charged with engine running from the low side. Took the compressor a min to come on but it did, and the 2 cans of ES-12A went in.

When you guys say system pressure should not exceed 50 psi on low side, is that idling? Mine will reach about 60 sometimes before the fans kick on and it lowers. If I give it some rpms, say 2500, the low side pressure drops to about 20 psi (dont know if thats normal).

I, too, think the issue is probably too much oil. Why else would the site glass be milky? When I pulled the vac, site glass was clear. As I recharged it got milky bubbles again and solid at full charge.

I know the internet is not the best place for this info, but this site is full of experts on this matter. I will listen and double check advice, but its good to hear from ppl on this forum.

Anyways...its blowing semi-cold at idle, and snowballs at speed. It seems like when Ive got air moving over the engine things work pretty well. I know this is indicative of the ES12A, but I was hoping for a little colder at idle.

How does one drain the oil on 87 300D ? And, do all those cans of ES12A contain oil too? If that the case, no wonder its got too much oil.