Hi there --

am extremely frustrated and as the mercury climbs near 100, wondering how I am gonna make it.

I have an 1980 300sd, 180k mi, love it to bits BUT it's freaking hot and I can't use the air, and this week the passenger window decided to crap out and I am going to die. Am working on the window, but really, I need the a/c working.

It worked intermittently first years I had the car. Last summer, it didn't come on. Took it to mechanic for freon charge, he said compressor and freon and solenoids were fine, that it was "a vent door stuck shut" and it would cost him $600+ to dig in and open the door (can you tell I am a woman and mechanics talk to me this way?). I said no thanks.

In ANY position the vents blow hot air. In defrost, the defroster blows lots of hot air. In lo-air, temp set at 68, it blows hot air. At hi-air, temp set at 85, it blows hot air. If I shut the CCU off, air shuts off. If I have it on at all, it blows hot hot hot air.

When I engage separate a/c switch, compressor turns on, power takes a hit, and hot hot hot air continues to merrily blow all around me.

I yanked the CCU tonight in desperation. I want to smash it to bits with a hammer. This is probably not going to fix it. Help. Please. help.

Welcome to the forum.

As you probably know, you've got a W116 chassis there. It has a climate control servo that is unlike any of the systems on the W123 or the 126.

You'll have to be patient as there are not all that many folks who have the W116, and even less that are knowledgeable on the function of the climate control system on it.

You said the compressor engages? Do the two hoses going to the comp change temperature? One should get hot (the hi pressure side) and one should get cold (low pressure or suction hose).
If so, the system is working. Just need to figure out why you're not getting the cooled air.

1984 300d Turbo 139k
Your Monovalve Is Defective, The Rubber Seal Inside The Valve, Replace The Seal Kit $50.00 Its On The Rear Engine Fire Wall With 2 Hot Water Hoses 2 Mounting Bolts And 4 Screws On Top To Replace
The Kit This Is Normal Open, It Close When A/c On

I agree - it sounds like the monovalve is bad - though there is no guarantee that it will be blowing cold when you fix it - at least it won't be blowing hot on you.

Once that is fixed it should be as simple as a recharge for you if the compressor is still kicking on we know there is likely to be pressure still in the system.

John

__________________
John Hughes, was in Landstuhl, Germany but currently in San Antonio, TX


1978 280CE Astral Silver now 59,xxx miles and counting "Silber-Kugel"
1986 300E Black Pearl Metallic 143,xxx miles 5-spd daily driver w/ blk leather "Schwarz-Schönheit"
1989 190E 2.6 (euro) 5-spd Desert Taupe 112,xxx kms Had to leave behind in Germany!!! "Helga"
1983 300D Pastel Beige now 312,xxx + miles SOLD

OBK#24

obviously I'd so much rather have it be the monovalve. I will follow the sage advice of someone here and take it to the a/c place for diagnostics, but am also going to feel the hoses and see if ac is getting cool. Do you think random a/c place will know about the monovolve? My mech didn't...

I do believe compressor is cooling, as I kept getting a very cool rush as we had hood open trying to figure it all out.

If it is the servo, I still love the 116s. But I'd really prefer it to be the monovalve. Any other diagnostics I can do to isolate that as a problem? I mean, ones that with my limited ability (couldn't even find compressor earlier) I can handle?

ps changed #9 fuse, just for back-up.

I'd have to agree that to look at the monovalve is the first thing to do. I bought a kit on eBay for about $20.

If you still have problems after it is replaced, then we'll have to do a deeper dive.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

I can't even find ANY hoses from what I thought was the compressor. There are wires, but no hoses.

and now my window is all screwed and half in, half out and I can't figure out why the assembly won't budge.

So I think I will just indulge in the girl solution and just sit here and cry.

this is so freaking frustrating and hard.

Does anyoen think the a/c place will be able to diagnose nd repair a monovalve problem? I can't even locate a freaking hose by mysel.f.

In front of the radiator is the condenser. It looks like a small radiator. This device dumps off the heat from the compressor. So, if you find the line that enters the condenser and follow it back........you'll get to the compressor.

There are two lines coming off the condenser. One goes to the compressor. One goes into the cabin to provide the fluid for cooling. Both of these lines will be fairly warm.

When you find the compressor, there will be a second line coming from the cabin. It will be relatively cold if the system is working properly.

A 1980 does not have a monovalve. It has the evil servo.

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

it has to be one or the other. It does or it does not? This may be the cause? An AC place may or may not be able to advise without ripping me off? Please, guys. money's tight and I am really suffering. Please help me.

It seemed like for me at least that 9 out of 10 times if I had a window "quit" it was due to corrosion at the switches/ wire harness in the center console.

I'd be willing to bet the A/C repair place wouldn't be familiar with the setup of the older MBs.

While not the most scientific way, I looked at the parts catalog and they had no listings for monovalve on your model.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

No, the window problem is that the gears of the lifting appartus no longer mesh. Theu've apparently just been meeting barely for years, and now just can't grip one another. I got the door panel opened and the lift halfway out, but there I am stuck, with the glass tilting perilously and no idea how to proceed. the good news is I leaning a ton. The bad news is that what I am learning is mostly what NOT to do.

I did replace the window switches with much success earlier this year. This time, the switch and motor are fine, it's the gears and the fact that I don't know what I am doing...

As far as the a/c, I really am afraid to take it to an a/c place if I don't know what to ask. They lean on your SO HARD for money and offer so little... last year it cost me $400 in a/c recharge and diagnostics to end up just as hot and frustrated as I am this year.

I so appreciate everyone's help. I just want to diagnose this and get some relief.

hey topanga
i'm hot too, can't use my AC either for other reasons (overheating engine). long story short, i'm in LA and found possibly 2 good MB mechanics who seem to know the old cars: Enrique in Tarzana at Mr. MB Motors and a guy named Nick at Stuttgart Motors in North Hollywood. I haven't been to Nick yet, so I can't personally recommend him, but he comes recommended by a helicopter mechanic I know who owns an 82 300D, says he knows his stuff.
hope this helps. i'm broke too and still a beginner and also have to rely on help from mechanics. tons of knowledgable people on this forum though, so keep looking around here.
good luck

__________________
1982 300TD, 265k
1984 300D, 282k

According to my resources, the 1980 300SD is indeed a W116 Chassis car. The early W126 cars came with the Servo style hvac system and had the buttons in the dash in a vertical line. Whereas the later W126 and the W123's after about '81 had the Monovalve and the buttons in the dash were in a horizontal line. Not a 100% sure, but I suspect that if the buttons are arranged vertical, it likely has the Servo like the early 126 SD's and 123's.

Go to the following site to see details about which year the various cars and chassis were available in the US.

http://home.hiwaay.net/~gbf/mbmodels.html

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150