SDL: low AC output (R12)
 

My 300SDL shows relatively high temperatures at the vents.
Temps are not going any lower than 10 -12C (50 -54F).
I have had the system apart, cleaned, new compressor, new condenser, new evap. and filled with R12. But maybe some air found its way in.
I already topped off one can R12 but still some bubbles at the glass and the pressures already high with not much improvement.
Can there be air in the system?

What would be decent temperatures at the vent on the stock system for the SDL?

Location: I am in Oman, Middle East with high ambient temperatures (recently 110/120F). Here is no one around who could vacuum, recover the R12 and refill. But I have another 4 cans with me, I also have gauges and a vacuum pump.


Martin

Honestly 50* out the vents with ambient temps of 110* is pretty good. I wouldn't expect much more than that.

Did you replace the dryer or expansion valve as well?

I did replace drier and evaporator with expansion valve with the new condenser.
In this country the SDL AC is not enough I have to say and I don't understand why there are still bubbles at the sight glass.
Are there any tests I could run?

What is your high and low side pressure readings?

Bubbles can mean low charge or leak.

This vent temp is at what ambient temp?

if you pressure tested free of leaks, vacuumed it out, and charged with the correct weight of R12, the coils are clean and new, the aux fan is running... it's doing all it can do.
the SDL has which compressor? sanden?

bubbles mean the liquid column of refrigerant is not solid. it's either low on refrigerant, or the ambient temp is above the design... (110°F certainly qualifies) what's the high pressure? what's the condenser liquid temp? I would do everything in my power to VERIFY zero outside air is mixing in.

At 110F., the high side pressure is going to scare you if the electric fan is not running. That's the first thing to check.

It might be possible that the system is low on R-12 with high pressure that appears a bit too high, when, in reality, it's fine at that temperature.

That compressor is quite capable in the SDL and I would expect the system to achieve 40F. at low fan speed at those ambients.

oh, and yes, if air or water is still in the lines, that will also show up as bubbles...

126 A/C Charts:

These might be helpful... didnt see one for the 603..

http://i.imgur.com/8Z5Tql.jpg

Based on a 95F (35C) outdoor temp, one should see between, 55-66 F depending on humidity.

Based on a 77F (25C) outdoor temp, one should see between, 48-53 F depending on humidity.

NFW those charts are accurate for the 603's Nippondenso compressor.

At 25C outdoor temperature, the Nippondenso will absolutely freeze the evaporator with air vent temperatures that are -2C.

At 30C. outdoor temp., the vent temp will still remain under 5C. with high humidity.

I'm not disagreeing with you, just posting the charts I found..

The 603/103's have the 10P15C compressor, the 116/117 have the 10P17C

IIRC, the 17C is a larger displacement unit, shouldn't it cool better than the 15C?

i was doing some AC research, when i came across some info that i believe answers your question in post#1 about seeing bubbles in the dryer window.

from the FSM:
"Note: An accurate check of the charge is not possible using the sight glass. At higher ambient temps(greater than 35C/95F) some bubbles may be visible with correct filling quantity."

I'm not quite sure what these numbers refer?

The 617 typically uses an R4 compressor and the charts appear to be a bit high even with that unit.

The 603 uses a completely different and much larger Nippondenso which does a much better job at cooling than the charts would suggest.

I think I had 225 - 250 psi on high side at maybe 100F ambient, but I need to verify that.

aux fan is running well. Correct amount of R12 I am nor so sure. i think I charged more but I am always a bit uncertain with the old cans...they sometimes seem to be low on R12.
I believe high side is around 250psi at 100F-110F ambient. Outside air is not mixing here.
I can see bubbles at these ambient temperatures...it is never below these temps right now and I see bubble all the time.
No idea about the condenser liquid temps. I can measure. Where? At the out let to the drier? I have a infrared thermometer.

Brian.....Nice!

If I am driving home in the late afternoon ambient is still around 100F+ and the car is cooked with 140/ 150 inside. Crazy.
It takes me around 10 miles until vent temps get down to 56F/ 60F....too long for me. So I am thinking something is wrong. After another 5 miles I can probably get down to 52/54 but that's it. In the morning it cools better when the car is still 'cold' with only 100 inside, almost same ambient.
Crazy desert here.
Martin

The 10P is the piston count of the compressor, the 15/17C is the displacement of the compressor 150 cm^3/r and 170 cm^3/r based on what I found online. For comparison the R4 is a 4-piston, 10 cubic inches, or 163 cubic inches unit.

R4:
http://i.imgur.com/1hNrkl.jpg

10PA15C:
http://i.imgur.com/olZhKl.jpg

10P17C:
http://i.imgur.com/8JQzFl.jpg

All well and good if you've got an R4.

Here's the Nippondenso:

https://encrypted-tbn1.google.com/im...HNEU6EiUQwvEQf

See any similarity............at all???

You have two issues going on there.

If the temperature of the evaporator is 140F., the freon must take all that heat out of the unit before the vent temps will stabilize at the capability of the compressor. In your case, it takes about 10 miles or so...............not abnormal for the amount of heat that must be removed.

What is abnormal is the final vent temp of 56F. I'm quite sure the system is capable of 42F. at 100F. ambients.



With high side pressures of 225-250 at 100F, I'm a bit suspicious that the system isn't fully charged. John can confirm it, but I would guess that the high side would need to approach 300 at that temperature.

If it were mine, I'd get a very solid steady state vent temperature after full stabilization at a given ambient and note the ambient.

Then, I'd add 3 ounces of refrigerant............by weight.

Then, take it out again and establish another steady state vent temperature after full stabilization. Hopefully, on the same day, with the same ambient.

If the vent temp drops, I would repeat the process with another 3 ounces.

Once the vent temp drops anywhere to anything near 40F., you're done.

Also, all of the above presumes that the compressor is running flat out..............NO CYCLING from the CCU.............if it is cycling, all bets are off. The problem is the Evap temp switch on the evaporator which is cycling the compressor at an elevated temperature (to prevent evaporator freeze). In your ambient, the compressor should NEVER cycle as it is impossible to freeze the evaporator.

Will spraying water on the condenser help with the 95% humidity in Oman? How about dual aux fans from a later 126?

Sixto
87 300D^2

I wasn't commenting on design similarities, merely displacement vs charts.

I'm just saying if you listen to the FSM's charts:

The top chart (110 engine) is for R4 compressor. The bottom chart is for 10P17C compressor. The R4, displacement wise, is slightly below the 10P17C at 163 cm^3.

If you base the numbers off the Mercedes charts and are to believe them, then the OP's vent temp should near the 110's charts as the 10P15C is 150 cm^3.

But I do agree, you should be able to get it down in the 40's. My 420SEL was able to do 48F at the vent 95-98F with high humidity.

220-270F based on the Ac Kits chart. Looks in range but maybe a bit low. You won't see 300 until you crack 110F. At least according to the charts.

http://www.ackits.com/aacf/ptchart.cfm

You continually refer to R4 charts and conclude that the vent temps should be near the 110's charts.............

I fail to grasp how those charts would be at all relevant to the Nippondenso compressor for which I provided a photograph and asked "see any similarities"?

I asked if you saw any similarities, because, in my mind, I see none.

My conclusion was simply based on a compressor displacement comparison. Which, in retrospect, is not the only indicator of performance. The R4 is a radial type where as the 10P15/17C are not. I also recall reading somewhere in the FSM that the later 126 cars AC system is capable of some 29/30,000 BTU, where as, according to that picture of the R4, is only at 24,000 BTU.

Ideally you'd find a chart like the 110/116/117 charts but for whatever reason Mercedes didn't include one or I've not been able to find one.

My 190E has a 10P15C installed on it. The center vent temp was able to get down to 38F with decently high ambient. 85-90F IIRC. However comparing w201 to w126 cooling system is not a good idea as the 201's center vents are within inches of the evaporator.

Ok, I got a bit confused when you posted data for both the R4 and the 10P15C in the same post.

I agree that the posted data for the 116/117 should be very close to the expected performance.

However, I do disagree with the tables. If one were to believe the tables, the compressor would never cycle unless the ambient temperature was below about 70F and the vent temperature would stabilize at whatever setting that the ETS would allow. The chart shows stabilization (flat curve) at about 45F.

This is certainly not the case and I observe both the R4 and the 10P15C cycling at any temperature up to about 95F. The R4 can maintain about 45F. at 90F. ambients and the 10P15C can maintain about 40F. at the same temperature. The 10P15C would still be right at the cycling limit at that ambient.

Hi Brian, thanks

No compressor cycling. I took the Klima relay out and replaced it with the ice cube. I got a new Klima relay but it is not working...I guess the compressor rpm input is cutting it out...I was dying, took it out and replaced it with the ice cube.

You as saying that the system should get below the 50s no matter what temperature/humidity it has to battle against.

So... at around 50/52F is the limit of my AC right now (very seldom vent temps reach below 50 for a short time) at ambient at 100-110, humidity around 60-70%.

Also I have the bubbles at the sight glass.

Fact is that vent temperatures are expected at the lower 40s
Reasons: You say there is probably not enough freon in the system.
I can charge another 3 oz R12 and see if anything is changed.

If nothing happens then it must be something else... water/air in the system...correct?

I will also measure the pressures and ambient temperatures more accurately and i wull measure the condenser temperatures at the intake/outlet

Does this sound like a plan?

ok.
refrigeration (and that's what auto air conditioning is) needs several things to cool.
first it needs correct volume of flow through the compressor, and it has to compress the gas well.
then the condenser needs the correct volume of tubing, unobstructed with oil or non-condensables. it also needs to be free of airflow across it's surface, and the fins need to be clean and clear.
the receiver needs to be mildly free of oil, and be un-obstructed, the desiccant needs to be clean and dry, the lines between all this need to be free and clear, and the volume of refrigerant needs to be correct.
all thats left is the expansion valve (TXV) and the evaporator coil. it has to function, and the coil needs to be free of obstructions, and the fins need to be able to pass cabin air freely through it. the blower has to work properly, and the air needs to be isolated from ambient air mix for maximum cooling to reach the cabin.

the only way to know if the correct amount of refrigerant is in the system is to weigh it.

if it has the right amount, and it's not cooling one or more of the other components are malfunctioning.

isolating which one requires several instruments, and a good understanding of what's going on, and the charts to find the flaw.

you need the exact ambient temp, and adequate flow across the condenser coil.
you need the temps incoming and outgoing from the coil along with pressure of the coil, and the known pressure drop across the coil...
you need the temp leaving the receiver, the temp entering the txv, the temp leaving the txv, the temp leaving the evaporator, the fan speed (low,medium, high, and you need to KNOW if it's blowing well)
you need the WET BULB temperature of air entering the evaporator, and the dry bulb air temp leaving the evaporator...

that's a LOT of information, but if you can gather it all, you can figure out exactly what's going wrong.

Naturally, the ambient temp is going to affect the final vent temp. However, at 110C, I'm still of the opinion that you can achieve 45 degrees on low fan speed.

The bubbles in the sight glass are a typical indication of low freon and the high side pressure also might be slightly low.

You don't need much more............in fact, I might add two ounces or even one ounce and see if the bubbles disappear and/or the vent temps drop slightly.

Having all the measurements as indicated above is all well and good, but quite unlikely in the middle of nowhere.

Update:

I have not done anything to the system.. It might be still low on freon, bubbles are still coming up.

I was changing the radiator and I see a total difference in cooling power! My engine was overheating all the times and the only explanation is the old radiator. The old one must have been restricting coolant flow and conductivity to a point when the engine was overheating. Now all is fine and engine keeps 90 C (while it showed 110 or close to 120 at 80/90 mph on the highway before)

Back to AC vent temps (the new radiator somehow improved the AC vent temps in a positive way slightly)
I have bought a digital thermometer in order to be more objective...
With ambient at 90+ F vent temperatures showed 7.5 - 8.5 C ( 45- 47F)
at 3000 rpm today with fan on low.

Do the numbers sound 'normal' to you?

Best Martin

I run R-12 in the 300SD. I installed a new drier, the correct amount of oil, a new expansion valve. I also adjust the ETR (evaporator temperature regulator) for better efficiency.

On a + 100°F in Palm Springs (with less than 20% humidity) and get about 40°F out the center vent on the freeway and about 50°-55°F in town at idle.

On 80° to 90°F days, it will drop all the way down to 33°F in the center vent, as evidenced by the photo attached.

As previousuly suggested, the fins need to be clean, the fan clutch in good shape (I use the 9 blade plastic fan exclusively) the oil amount must be exact, the R-12 charge precise and the ETR adjusted for lowest vent temperatures.

Mercedes-Benz has a chart that 'suggests' normal vent temps based on ambient temperatures.

Your 45°-47°F vent temps are pretty good. I have an adjustable switch on my A/C that allows me to bring the auxillary fan in at a lower temp/pressure. This and a GOOD fan clutch help tremendously.

Keep in mind that a W116 will overheat without a fan, even at 60-70 mph, so the fan is critical at road speeds too, though many will argue the point.

Regards,

Thanks Bert.... I have a 603 engine , 300SDL, W126
As the car was overheating at higher speeds I changed the radiator, pump and T-stat (Behr 80 degrees)...
and through magic cooling temps are down to normal (about 90 C at all speeds!...even when I am driving 90 mph for some time).

This somehow affected my AC vent temps as a side effect.
Vent temps dropped by about 2 degrees C or 4 F. I can tell because here are the same conditions all the time...there are 2 days with partially rain..but the rest of year it is sunny and identical, boring and hot as hell.

A recent shot of my W116 center vent on a 90°F day with 21% humidity...

Hi Dr. ,

I was testing if I could improve my fan clutch on my 300 SEL 3.5. If this experiment is successful I'll also do the clutch on my 300SDL. I agree that this clutch needs to work properly. No question. At speeds and hot the fan must 'haul' and stop at the moment when the engine stops. Anything else causes problems.