300DT AC controls (1983)

[coachgeo]

I've read in here all about the issues with the 300 AC system. At the moment I dont have questions that relate to these issues. I checked the online manuel but that manuel's (Skinner FSM) General description of the function buttons of the AC are somewhat different than the buttons and knobs I have.

My questions are simple. How the hell do you turn it on, control temp etc. Right now I have nothing but heat no matter how I set the buttons. but then again I dont have a clue what switches are what.

I see a verticle orineted temp. roller nob. It seems to roll from a blue section to a red section. I assume blue is cool and red is hot. There is an EC push button. In the same row of buttons with the EC there are several buttons with up and down arrows. The arrows are either outlined in white or filled in with white.
There is also one button that is an outlined white circle.

Again the car is an 83 300DT

For a properly operating CC system simply set the temp dial to about 25 and leave it there or adjust it a few degrees one way or the other for your own comfort. DON'T set it on Max or Min. Let the system automatically adjust temp for you.

Then press the button that has a solid white up arrow and a solid white down arrow. Then press the fan button that says auto.

If it is working correctly that's all you need to do. If it is blowing real HEAT all the time, the problem is likely to be the monovalve that has four screws in the top and it's near the battery. This is a common problem.

Another common problem is that the hose on the climate control temp sensor disintegrates and disappears. This is that little grill in the upper center of the dash. Remove the glove box and look behind it. There should be a hose that goes across to the left of the glove box to that sensor below the little grill. Go to home depot and get 3/4" foam hose that is used to insulate pipes in the winter time. Cut a section the right length and put it in place.

These are the two common failures of the climate control system. This does not take into account the refrigeration system. If it has freon, and everything above is set and checked the compressor should kick in. If it doesn't it is probably low on refrigerant and will have to be seen to.

Good luck,

[coachgeo]

UPDATED since posting this

Thanks Larry.

I knew about the foam hose issues and I would figure a car this old has probably leaked out the AC refrigerant by now. I just wasnt sure cause I did not even know how to turn it on.

BTW. I found a blown fuse that affected the rt. two running lights anddddd..... the EC. I installed a new one and now have cool air or hot air as set by the temp dial.

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UPDATE: read another thread that mentioned fuse #14 and its connection with the monovalve. This is the fuse that was out on my car. Explains why I now have a working (or partially working) environmental Control system.
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That was at night when it was just a little cool outside, and I actually had to set the temp controll to slightly warm to be comfortable. I suspect that for now I will not have cool air in the day time. I'm assuming the cool air from the vents was cool outside air being brought inside and NOT the AC working. Time will tell. At least the EC's Temp control system appears to be working.

How do you just turn on a "Vent" NO AC just blowing in air from out side?

[sixto]

Originally posted by coachgeo
How do you just turn on a "Vent" NO AC just blowing in air from out side? [/B]

Press the button with EC in the middle, if it has such a button.

Sixto
95 S420
87 300SDL

[coachgeo]

Originally posted by coachgeo
How do you just turn on a "Vent" NO AC just blowing in air from out side?

Originally posted by sixto
Press the button with EC in the middle, if it has such a button.

I thought EC (Environmental Control); which I have, was the button you push for the system to "automaticaly" control where the air comes from (heated, AC, or vented air)? My question was what button do you push to NOT use the automatic system but just vent some air in from the outside.

Guess Im thinking it works like a good high dollar 35mm camera. You can set things to either be fully automatic or fully manuel. Is this not the case?

[psfred]

The buttons are, from left to right, defrost (full heat, all the air to the windshield), split flow (some air to floor and to windshield all the time, nice for winter driving), full automatic floor/dash vents (no defrost flow), EC (economy -- works like the previous button but without the AC compressor) and ) for OFF.

There are three vertically arranged fan buttons -- bottom is low (don't use this in really cold weather, you feet may freeze from low airflow), auto, and high.

There is some "float" on the temp setting -- my 300D tends to run a bit cool, so I sometimes have to set it warmer a few degrees on cool days to keep cold air from blowing on me. Less of a problem on EC since the AC isn't running with reheat. Small adjustments are needed from time to time.

If you still have poor temp control, or the unit switches modes constantly with contant operation of the switchover valves (lots of clicking noises from the dash), the pushbutton control unit needs to be resoldered or, if that doesn't fix it, replaced.

Peter

[lietuviai]

Originally posted by LarryBible
Another common problem is that the hose on the climate control temp sensor disintegrates and disappears. This is that little grill in the upper center of the dash. Remove the glove box and look behind it. There should be a hose that goes across to the left of the glove box to that sensor below the little grill. Go to home depot and get 3/4" foam hose that is used to insulate pipes in the winter time. Cut a section the right length and put it in place.

I wonder if it matters that you need to use a foam hose. I used a piece of old garden hose that was about the same diameter and everything seems to work fine.

[sixto]

Originally posted by psfred
The buttons are, from left to right, defrost (full heat, all the air to the windshield), ...

I'm sure Peter meant to include -> AC compressor engaged for dehumidifying and recirc mode engaged too.

There is no manual control of center vents, intermediate fan speed and until 1986, cabin air recirculation. Basically, there is no manual control as you know it on other cars with ACC.

Sixto
95 S420
87 300SDL

The garden hose will work but will not give the temp sensor an air sample that is an accurate sample. The foam hose has lots of insulation capability so the air that hits the sensor is pretty much the same temp as it was when drawn into the hose.

Have a great day,

[coachgeo]

Originally posted by psfred
The buttons are,....

Peter

Mucho thanks Pete and Sixto

[sixto]

Originally posted by LarryBible
The garden hose will work but will not give the temp sensor an air sample that is an accurate sample. The foam hose has lots of insulation capability so the air that hits the sensor is pretty much the same temp as it was when drawn into the hose.

Larry,

I thought the sensor was right behind the dash or dome light grille? It shouldn't matter what the temp change is between the sensor and the aspirator motor since, right? Or do some MBs have the sensor at the far end of the hose?

Sixto
95 S420
87 300SDL

sixto,

It depends on the chassis, the 124 sensor is down low and the air is drawn through the grill at the rear view mirror down to the sensor.

The late 123 chassis, as was the original question in this thread, the sensor is indeed behind the grill, but the air is drawn over the sensor by the draft drawn through the foam tube that disintegrates over time.

I don't know where the sensor is located on the 126 or 140 chassis. I'm a poor boy and have to drive the little cars.

Regardless of whether the sesnsor is five feet away or right at the grill, air must be drawn through the grill someway.

Good luck,

[lietuviai]

It looks like my sensor is on the top of the dash in the center, is that it? Its a small square button that looks like it has a grille pattern.