Hi there. I am really hoping someone here has the answer. I have a 1986 560sl that has been in and out of the shop for the past 3 months. It is really starting to wear on me since the problem has not been resolved and it is just so hot here in Texas and the $ I have invested in this issue already. I recently had the compressor replaced since I was told the clutch was burned up and I was not getting cold air. Converted the freonto the newer freon, expansion valve was replaced as well as the drier and the a/c relay switch. Still no cold air. Okay, now have recently replaced the push button control module. Got cold air but not for long.

Here seems to be the problem....When I am accelerating the cold air kicks in and blows, if in traffic and barely moving in 95 degree temps then I just get air. Any suggestions? A bit of freon was added last week but we are still at the same problem this week. HELP Please! Thank you all!

Does the engine over-heat?

Sounds like your auxilary electric fan (the one in front of the radiator) is not kicking in...so no air flow in traffic.

You can check by getting car hot, pulling over with AC on "MIN" setting - popping hood and looking to see if the fan is going...you will be able to see and hear it.

Sounds like you have replaced the other components that come to mind.

Check if something is stopping the fan from turning (stick or other debris), fuse is blown, etc.

Good luck.

JFawcett, thank you for the reply! I have not noticed my engine overheating. I will check the auxillary fan as you suggest and see if that could be causing this problem. I just want to get to the bottom of this. I have only had this car 1.5 years and not quite ready to give up on it.

I know you can definitely understand about the heat in Texas! Thank you again.

Wait until July & August!

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE

Have the viscous fan clutch checked also. Low air flow across the condensor is a major cause of complaints of poor A/C at idle (or real slow).

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

If you paid a shop to replace the stack of parts mentioned in your opening post and you have no cold air after all that work and your $$$$, I would take it back and DEMAND that they resolve it.

That aside, there have been many posts here about 126 owners converting from the original R-12 to the newer R-134A. Not many have been pleased with the outcome.

I do not believe the refrigerant issue in itself is your problem because you say no cold air. However, if the shop you used improves upon you current situation, do not be surprised if you never feel like the system is really getting it done.

As far as I'm concerned, R-12 is the only refrigerant to use in a 126 car.

Just my 2 cents.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

one thing you could do since condensing is the big issue with 134a is to take out condensor and using mag wheel cleaner[weak acid] clean all the black paint off the tubes and fins.this will give 25-30% improvement in efficiency.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg

Not enough air flow over the condensor could not only reduce the cooling efficiency BUT can also cause the compressor to cut-off because of excessively high pressure on the high side. So either the condensor fan is not operating or it is not operating in the correct direction (i.e. the flow should be from the outside towards the inside). I am not familiar with this car but on my 260E there is a temperature sensor on the engine block which sends signals to the climate control relay, and if this is bad, it could cause the relay to cut-off the compressor. So while you are idling, check the condensor fan and also check if the compressor clutch is actually running when the air blowing is hot. Have you checked the pressures ? What are they 1. when you do get cold air and 2. when you dont ?

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Saumil S. Patel

Without A/C manifold gauges it's hard to evaluate your system, but with a little common sense you should be able to find the problem. I have experienced your exact problem when my Aux. Fuse was blown. Replaced the fuse and all has been well since.

If your A/C is cooling when driving but not in heavy traffic, then the Auxiliary Fan is probably the problem. If it were me, I would jumper the connectors at the Auxiliary Fan Temp. Switch at the Receiver Drier (this is the one with the pigtails). This way, the fans are operating when the engine is running and you can test your A/C cooling temperatures while driving in heavy traffic and also test your fans to make sure they are operating. If the Aux. Fan doesn't operate, then check the fuse and the Aux. Fan Relay.

You have received a lot of good advice from fellow members so far.

Good luck,

Dave

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

I beg to differ on my 87 420 SEL I had the same problem and I changed the expansion valve, evaporator, and dryer with new switches.

When I pulled out the evaporator its fins were packed with years of dirt and other debris. Not allowing the blower fan to draw enough airflow to produce a good cooling result at a stand still.

After installing the expansion valve, evaporator, dryer with new switches, vacuuming the system and charging it with 134a my system runs at a cool 42 degrees at the center vents.

I am not suggesting for someone to hire someone to change the evaporator since it is like open-heart surgery and a 22-hour operation and would cost thousands for someone other than yourself to do.

But if you are capable of performing such a task then do so it is well worth it!

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William
________________________________________
1987 420 SEL - Like a fine wine only better with age

Thank you for your reply wscheffer. I really appreciate it. It makes sense to me. The guy who installed the new compressor for me along with the expansion valve and drier, did inform me he was going to blow the expansion valve clean. He had my car for a cpl of weeks. I am under the assumption he did that but I will have it checked.

Thank you so much for your help.

I love this site. I do get great info. I am really feeling at the end of the rope on this a/c problem and now that I have some suggestions, I am feeling hopeful. Thank you. I will see today as suggested to pull over and see if I can see the auxillary fan and condensor fan moving while in afternoon traffic. And of course, I will take it to the shop again with these suggestions and see if we can get my baby running good again. I will also take the great advice and have the fins and tubes cleaned to get as much cold air as I can. Thank you all. I will keep you updated!

The AUX fan as activated by the switch on the dryer...

The current runs thru a big resistor near the compressor. They sometimes go bad.

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2012 E350
2006 Callaway SC560

Hi Fpilot,
I had a very similar problem on my '82 380SL, and it turned out that the air conditioner was valiantly struggling to cool the car, but the monovalve was opening up at low engine speeds because the auxiliary water pump had quit working, which allowed hot water to enter the heater, totally negating the efforts of the AC system. When I would speed up to normal highway speeds the car would cool right down because the monovalve had enough water pressure provided by the engine's water pump to start working. (ie, closing it's valve.) The monovalve requires that the auxiliary water pump works to provide enough water pressure to hold the monovalve closed when the engine is running at low speeds. The valve is made just like the valve in your dishwasher or clothes washer, ie, it has a small primary valve that opens to allow water pressure to shut off the main valve. If there isn't enough pressure, the valve will dribble hot water into the heater, making the AC ineffective.
What I did was to replace both the monovalve and the auxiliary water pump with a vacuum operated valve that positively opens and closes regardless of the water pressure. I used a switchover valve (electrically operated vacuum solenoid valve) which is operated by the electrical lines that went to the monovalve and controls the vacuum to the new vacuum valve. The whole conversion only took an hour or so, and the results are totally amazing! Now the car stays really cool in hot weather, regardless of speed, from idle to freeway speeds, and a side effect is that the engine runs cooler in hot weather because it isn't trying to both heat and cool the same air.
If you think about it, the SL's cabin is pretty small, and really doesn't take a massive air conditioning unit to keep it cool, as long as it's working well. I posted the details of my change on a thread in the diesel pages, as someone there was having a similar problem, here's the thread with details...

Mono Valve Voltages

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C

Drive down from Ohio to say Houston, Texas this July. Spend a couple of days there driving around in stop-n-go rush our traffic. After that, head west to Phoenix, Arizona and do the same.

Check back in here afterwards and let us know how you feel about R-134A in your 126.

It may work in Ohio during the summer. Few if any who live in REALLY hot climates have had anything good to say about R-134A in a 126 car.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"