R134 level is up to full, but I have had to top off a couple times this summer. I put dye in it last month and found a leak at the top of my expansion valve (as a side note I've never seen an expansion valve leak - it's not leaking from a seal but from the seam between the diaphram and housing of the valve!). The valve is also on order.

The car is a 1987 300e. There is no cabin filter and there does seem to be sufficient airflow from the vents.

I had a very similar problem with my '85 XJ-6. Its cabin temp sensor is right under the dash. It was drawing air from the vents into the temp sensor, so when it was pumping cold air into the vents, it would think the cabin was cold and start pumping heat. It would yo yo continuously like this and took me a couple years to figure out what was going on. I'm wondering exactly where the cabin temp sensor is in my MB. Is the sensor in the ceiling where the little air grill is, or is the actual sensor located behind the glovebox where the fan is? If it's behind the glovebox then there are probably lots of places where I could be leaking air from places other than the cabin. On the other hand, if the sensor is located in the ceiling, then I've got bigger problems.

Thanks all for your help.

Bob Kopicki