Hello

Lately its been hot and humid in Southern Ontario.

I was stuck in a rush hour traffic with the AC going and I noticed my car running much warmer, usually it howevers just a needle width above the 85C mark but today it was 1/2 way between 100 and 120.

Now if I run the car on the Economy setting, ac compress off, the car would hold a steady 90C temp.

Any ideas? My first guess would be the high speed fans.

i agree... check them. also you might check freon level.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

If this only happens in traffic, I would suspect the fans. If you have overheating at other speeds I would suspect a coolant flow issue, such as a partially clogged radiator or a worn/crap encrusted impeller on the water pump. I don't think that low freon would cause this, but a clogged expansion valve might. As freon level drops so does high side pressure, which reduces superheat, which means that the air flowing through the condensor to the radiator won't be as hot. A restricted expansion valve will cause high side pressure to increase dramatically, which will make the condensor very hot. The hotter the condensor, the hotter the air going to the radiator. It's probably just a fan issue, though .

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1982 300D, black w/ palomino leather, 203K
2001 E320, champagne, 105K (Mom's)
1999 Dodge Dakota, squeaky & battered, 142K

My guess would be that the fans are not coming on at low speed. I have the same issue but haven't figured out why they are not coming on. Check out this thread which is helpful but not conclusive.

95 E300D fans don't run at low speed

I am also going to check the pressure in the A/C system, as someone suggested that low refridgerant could be the culprit.

Common problem on these cars. Pull the cover off the rear portion of the fuse box under the hood and you will find the Blue (low speed) and Green (high speed) aux fan relays. They have fuses right on them. The low speed relay fuse blows all the time from constant use. I think it's a 15a fuse.
A new fuse should get you several more years of fan operation.

Good luck.
Dr.D

__________________
Dr.Diesel -
Shop Foreman
Master Guild Mercedes-Benz Technician.

Think the dealer is expensive? Do you know how much it costs to train a dealer tech? Or buy the required MB special tools to have on hand?

Dr.D.

Thanks for that info. My fuse was indeed blown.

Now the fans come on at low speed as they should.

Here a some pics for those that may also run into this problem.

To access the rear panel you need to remove six screws and lift off the cover. You can see the blue and green relays. The second picture is the low speed relay, and blown fuse.

Attached Thumbnails

   

This also applies to gas powered W124's as well. The 400/500E's are pretty
notorious for this but, the E320 is just as common.
Too small a fuse I would have to guess.
Glad you fixed it.
Dr.D

__________________
Dr.Diesel -
Shop Foreman
Master Guild Mercedes-Benz Technician.

Think the dealer is expensive? Do you know how much it costs to train a dealer tech? Or buy the required MB special tools to have on hand?

Thanks everyone

I took the cover off to get to the fuses and I found a blown fuse indeed. The low speed aux fan fuse was blown. I got a new one and now the aux fans come on when ac engaged!