Honeywell DT90E compatibility
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Joined: Wed Oct 31, 2012 2:06 pm

Honeywell DT90E compatibility

by seanxb » Wed Oct 31, 2012 2:28 pm

I am replacing an old dial honeywell room stat (42003840-001) with a digital DT90E.

I am unsure about the wiring compatibility and wondered if someone could clarify please?

Currently, I have 3 wires - Blue, Yellow and Red.

The blue is inline with a resistor and then tied to the yellow, which is then connected to what I assume is the thermistor. Indicidentally, Blue is in terminal no.2 and yellow in no.3.
The red wire is in terminal 1 and this runs to the other side of the thermistor.

The new unit has three terminals only, A which is marked as Live, B which is marked as neutral via a resistor symbol and C, which is not marked but on the diagram, it looks like it is internally connected via a switch to A.

Question being, where do my Blu, Yellow and Red wires go on the new unit?

Any help would be most appreciated.

Thank you,