Similar (but not the same) problem with 190D (1985).
When driving with the heater button ON and set for heating (about 22-24C) the car seems to cycle from heat to cold to heat. So, for instance I get the heat until the car (interior) is warm, and then the climate control clicks and the AC comes on, until the heater kicks ON again. and so forth... This does not happen with the EC (Economy) button pressed ON. Because my AC was kaput last winter, I don't know if it's normal.
On top of that, when in the EC mode, the heater seems to get stuck and I have to "restart"it by moving the temp control to max (only happened twice). Any thoughts??????

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1985 190D 2.2l Sold-to Brother-in-law
1996 Mustang 3.8l -"thinks it's a sports car"
1988 Grand Wagoneer - Sold (good home)
1995 Grand Cherokee Ltd -"What was I thinking??!!"