My blowers (both cars) do not delay for the heat to rise above the cabin temp.
But both ACC units seem to work. they slow the blower at least when the car gets warm.

Where do I start to look for this, or what term would I search for?

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83 300SD Dark Silver Dark brown inside

There's a temperature sensor on the engine (thermostat housing?) which regulates the feature. On defrost the blower should always run, it bypasses the temperature sensor.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Is this seperate, or the same that send the signal to the gauge?
I will look at that. Anyone know what it should read cold and hot (ohms)?
thanks

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83 300SD Dark Silver Dark brown inside

It's separate. The gauge sender is on the left side of the block, and the HVAC sender is in the thermostat housing.

It's not a "sender." It's just a switch; it should be open when cold and should close at approx 100 degrees F. When the switch closes, it provides a ground path for a relay in the CCU.

If yours does not delay the blower its possible that the switch failed in the closed position. Sometimes they fail open and then the blower doesn't come on at all. Our 300D had that happen, so I just grounded it out.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
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'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Pull the wire off the switch on the thermostat housing.

If the blower shuts down, the switch is the problem.

If the blower continues to run, the CCU is likely the problem.