After research I thought this was due to the duo valve so I replaced it and the symptoms did not change: constant heat unless AC is set to MAX.

I tested the valve I removed and found:
1) Taller cylinder seems to be a pump and it buzzes (turns?) with 12V
2) Smaller cylinder is the magnetic valve and it seems to close properly. I blew air into it with my hand on the other three ports and it stopped with 12V applied so I likely replaced a good valve!

The climate controller (cc) seems to operate for each button.

I rechecked the connector(s) voltages with engine on:
1) cc off: valve 11.90 (closed), pump 0.60 OK
2) cc & blower on, knob to cold: valve 0.56 (open), pump 11.43 (on) CONSTANT HEAT
3) cc & blower on, knob set to max cold: valve 11.82 (closed), pump .72 OK

Just to confirm, the L shaped connector is for the valve and the flat connector is for the pump?

I've swapped a cc with no change. Any ideas what to check next? Thanks in advance!

Attached Thumbnails

 

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'88 300TE, 175k, black RENNTech 3.6L Recaro C's AMG 1 SOLD
'92 500E, 110k, Spruce green, stock SOLD
'94 E320 Cabriolet, 130k, E500 wheels, Emerald green SOLD
'94 E320 Cabriolet, 110k, black, stock, SOLD
'88 300TE, 229k, dark grey, SOLD
'90 300CE, 212k, white, new paint, SOLD
'91 300E, 209k, white, rebuilt head SOLD
'74 914-6, grey, 2.7L 325hp twin turbo Audi conversion

Interior heat sensors.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
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