When I am running my a/c, I notice that when I stop at a stoplight or am stuck in traffic the temp. gauge rises very high. When I proceed in normal traffic it goes down. I also noticed that my in-dash outside temp. gauge no longer works. Are the two in correlation with each other?. I plan to take the car to my indy. next week and I wanted to be able to give them some idea as to what is really going on with this car. The car is a 1993 300e. Thanks in advance.

test your viscous fan clutch using the broomstick method, also check the electrix aux fan(s). If those check out, look for oil sludge in your coolant reservoir and/or an oil leak towards the rear passenger side of the cylinder head where it meets the block.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

First suspect for that condition is the a/c low speed aux fans/circuit and the two most probable causes for that system failure are the fuse or a slightly low refrigerant condition.

The easy test for this circuit is to put the key on and jumper the two spade connectors at the end of the high pressure sensor wire .... at the a/c reciever/drier..this is the sensor with the 6" pigtail wire leads . IF the fan comes On w/jumper, the4 circuit is verified and the suspect is low refrig....if No, then the suspect is the low fan relay/fuse/ or Resistor, with the fuse being the first suspect ..

__________________
A Dalton

what about the outside temp. gauge in the dash? Is that related to the aux. fan or fuse?

No

Low aux fan has ONE function..to add additional airflow across the a/c condenser when the high pressure switch senses that there is a HIGH THERMAL LOAD on the a/c system and it is being TAXED.....that circuit is a simple 12 volt/ relay circuit with only one controlling sensor ..
That sensor is the one I mention in the Low Fan jumper Test.

If the low fan does not come on and the a/c is experiencing a high thermal load , [ which happens in slow traffic or stop/idle conditions because of low airflow with a stopped/slow moving car] , then the radiator gets heated from the passive heat radiation of the a/c condenser ...simple. The results ..you over-heat the coolant system. And the most often over-looked cause of such a condition is the a/c system is just a little low on refrigerant...allowing for a/c operation, but not good enough to trigger the low fan switch that I have you jumper.
So test that first, before you do all the other things you are going to be told are bad....

__________________
A Dalton

If you find that the viscous clutch is dead, or well on it's way out, I ended up with a euro spec one that had barely been used before the owner of the car found his dream car and parted out the 500SEL that he had been driving.

I bought it, but then the electric conversion finally arrived, so I didn't need it.

__________________
-Josh
Testing the cheap Mercedes axiom, one bolt at a time...

Yesterday when my wife got home, I went out to her car to see if the aux. fan was running. It was not running. I figured that if she drove the car 10 miles from work the fan would be running shortly after she cut the car off. I pulled the hood and checked the aux. fan fuse and sure enough it was blown. I replaced the fuse and the aux. fan came on. Today when she comes home I will drive the car and see if the temp. gauge goes up when I stop at a stoplight. Being that the problem was a blown fuse, do I still need to check for low refrigerant? Also the outside temp. gauge is not working anymore. I checked the fuse for it also, but it is not blown. The outside temp. gauge is on the same fuse as the turn signals. The turn signals work, but the outside temp. gauge does not. Thank you Arthur Dalton for your advice!!.

how high does it go up? It seems normal that the temp should rise with the a/c on and in stop and go traffic. Mine does.

__________________
1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

It was going up almost to the 120 degree celsius line. I drove it today with the air on and it seemed to stay between the 80 and 100 degree celsius line. It appears that the aux. fuse was the culprit.

Very Good.

The fan for a/c operation is the LOW speed .. yuo have taken care of that one...Now, you can now check the High fan for proper operation by simply turning key to RUN position and unplugging the 2 wire blue sensor at the thermostat housing..that should give you high fan for coolant temp protection

__________________
A Dalton