I have a 1991 300D. While the car is in motion(normal flow of treaffic) the a/c works just fine, but at slow speeds or when idling it doesn't maintain the temperature. When sitting in traffic it seems like the air starts getting warm or it's just not as cold. What could be the cause of this?

You really need to share what kind of car you are talking about.
You need to check your viscous fan if you have one.
You need to check your aux fan if you have one.
You need to clean both sides of both your radiator and your condensor.
You need to see that your engine fan shroud is intact and positioned correctly.

If it cools fine ' at speed' then these are the most logical and cheapest things to look at first.

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Our mind reading skills are quite weak here at Mercedesshop. What year and model are you dealing with? Is it safe to assume that it is a Mercedes Benz?

If you have a W123 then that is common, almost normal. {with any refrigerant}


Same pretty much for pre-'93 W124's too I believe. Especially if converted to R134a. {since I was able to read your mind}

Put your car in your signature or in the body of your question. It is a pain to have to go look at your profile to find the info, and annoys those above who are most likely to have your information.

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Sorry Jimmy, I have to disagree. Now that my 123 has been repaired my wife insists on driving it to pickup the grandkids after school. The only reason is (compared to her new Lincoln) she can idle in the pickup line (might be 100+ outside with a 10+ minute wait) and the car stays nice and cool.

Sorry OP, I can't help cause I'm not as good of a mind reader.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html

Low charge.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

I apologize guys. I have a 1991 300D. From reading a few of the other threads, I believe that one of the fans should come on as soon as I turn my a/c on. Well, it doesn't. I'm not sure which side should come on, or where to start troubleshooting the problem.

Both fans come on. They are wired together. If only one is running only one needs to be replaced. Had similar problem. They run at 2 speeds.
Bob

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92 300D 2.5L OM602 OBK #59

Neither one of them come on when I turn on the a/c. Aren't they suppose to come on at a low speed? I let the car idle with the a/c on one day last week....the fans kickicked on at high speed to prevent the car from over heating. The inside of the car never quite got cool while it was idling. I drove it about 6 miles before I let it idle.

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1995 E420 152k
1991 300D 2.5 348116 daily driver
1992 300E 2.6 196k-work in progress(head gasket)
2002 BMW 745Li 93k

Here's my thread of the aux fans for the W124 300D.

It should help.

W124 92 300D OM602 Aux Fan Question/Trouble Shooting

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92 300D 2.5L OM602 OBK #59