Well, ya'll have been so helpful thusfar today, I'll troll again for wisdom.

Same 300E as I thought burns too much oil (turns out it's probably normal consumption) has extremely poor temperature control in the people tank. I understand that this is "climate controlled" and should try to maintain a constant temp by automatically adjusting the heater and/or AC.

To begin, the temp knob has no markings, so I can't make a judgement as to what temp it should be trying to regulate. That's ok, were it not for the fact that the only position in which it seems to produce any heat at all is in the fully "up" position. I assume that this is the equivalent of the highest temperature marked. Any other position results in very cold temps in the car. (Very cold is relative, however, 65 degrees here in California is freezing to most of us, but that's downright warm for other places.)

The fan does vary in speed, but no consistent temp is maintained, regardless of how it blows.

I've seen in other posts 2 things that seem promising. First is the "mono" valve and the other is the "temp controller" that is behind the glovebox (though this was described for a '85 300TDT - similar to mine?)

Are either of these two things likely culprits and reasonable candidates for replacement? Other ideas?

Thanks!

Sean

No, the '85 300tdt bears very little similarity. Your car has no monovalve although it has a heater control valve that some folks will mistakenly call a monovalve. Forget about comments from those who are familiar with the earlier car and not familiar with yours.

From your symptoms, the first thing I would check would be to see that the system is drawing a cabin air sample over the temp sensor. There is a little grille near the inside rear view mirror. From that is a tube that snakes around to a little fan motor that draws air and blows it across the temp sensor.

To check it, put some smoke near the grille while the ignition switch is ON and ensure that the smoke is drawn through the grille. If not find the little fan motor and see if it is turning. If not, check for voltage. If voltage is present, replace the fan motor.

The location of the fan motor varies throughout the 124 series. Mine is in front of and to the right of the glove box. It is easy enough to remove the glove box and look for it there. If it isn't there, it may be somewhere near the center console.

Best of luck,

If you're taking out the glove box, you should also check the vacuum lines coming off the distribution block to the left of the glove box opening. While they mostly control routing of air to different vents, one of them controls a flap that mixes hot and cold air. If this is not working, it may be part of the problem. Should be the line attached to port #6.

Edit: you should check that the line holds vacuum, meaning that the part on the other end of the line still works.

I did some digging this weekend and the sensor pump by the mirror appears to be working just fine. Reading some of the troubleshooting pages in the manual suggests that I may have a vacuum problem. Severl of the posts here talk about a MityVac which JC Whitney shows as being a vacuum tester for about $40. Here's the URL that I found it at.

http://www.jcwhitney.com/webapp/wcs/stores/servlet/ProductDisplay?productId=520&catalogId=10101&langId=-1&storeId=10101

Is there something else that I should have too?

Thanks!

Sean