I am having an issue with the HVAC in my 190E. The defrost flap is always open and the heat would come on with the AC.

I first checked the heater valve and it was fine, so I suspected either the vacuum module or the HVAC control panel. I swapped the control panel with another one which I am not sure is good but it worked the same way as the original so I decided to check the vacuum control module. I had swapped it out before with another one when I first started having issues earlier this year but it didn't change anything. I just figure it is probably this module because it gets incredibly hot and it works for a few of the vacuum flaps but not others. I tested each of the vacuum flaps and found the defrost flap circuit is not holding any vacuum so either there is a line broken or disconnected or the pod is bad. Everything else held vacuum. The module can open and close the floor vents and recirculate flaps but heater box flap and heater valve are always open.

My guess is the solenoids for those valves have gone bad or are failing, which is why the unit gets incredibly hot. I might try to upload a picture tomorrow but the circuit board for the module has definitely been hot, right at the solenoids for the heater box flap and the heater valve.

I'll try testing the function and resistance of the solenoids and swap some around between the two units at the Invention Studio at GA Tech but I am wondering if anyone else has had this issue. The module in the W201 is behind the glove box and there are two versions, the early version is two separate pieces with a vacuum connector between the two (IIRC) and the later style is one piece.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.