Apparently the ECC dash unit for the 850 is the same from 93-97. However, I have noticed the wiring harness plug is available in a green plastic or yellow plastic. Mine has green plastic wiring harness plugs. Does the color of the plugs matter? Are they inter changeable?

I would stay with the green, only because I don't know where the yellow was used. It could be for RHD? Obviously, yellow belongs in a different wiring schematic than the green.
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My back feels better when I sit in a Volvo seat

Thanks for the response Klaus. My original 93 850 ECC had a green plug. Today I got two units from a friend who pulled the parts from a Pick and Pay. One has a green plug the other is yellow. He told me that both male plugs in the donor cars were green. Haven't had the chance to try one yet...will do tomorrow and report back. I am hoping this solves my problems.

Just to be helpful, you may need to clear the codes in B-1. Unplugging the unit will not clear any codes.
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My back feels better when I sit in a Volvo seat

Right Klaus. I installed the green plug ECC unit and cleared the codes. None of the B1 codes returned and I have some control over the blower speed although it does not appear to be as forceful as below. The "Auto" function does not appear to function at all. Curiously, I am now getting the ABS dash light and code 444 from the A3 port. Could these seemingly unrelated issues be a faulty electrical ignition switch beginning to manifest itself?

The only time I got an ABS pump failure, my daughter drove through a couple of inches of water - at speed - and got the wiring very wet. A couple of days of drying solved that, along with clearing the code and then driving the car above 20mph for the self-check. An ABS pump failure is quite rare.

The auto blower speed depends on outside temp and in cabin temp selection. If the engine is cold and it is not hot out, the blower will probably not run until the engine coolant gets above minimum.

If you are pushing the blower speed to max, then it should be getting 12V and blowing like crazy. It could be that the blower is getting old and the commutators are getting threadbare and not making good contact.

It is possible that the 'temp' dials on the new ECC are not calibrated the same as on your old one and you may need to adjust the temp up/down from the previous position.

No codes are a good thing, but something else to think about: The vent positions could be compromised with the new ECC. You might have to run mode 999 to recalibrate all of the vent positions. If you have a Haynes manual, there is an explanation of how to do this...
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My back feels better when I sit in a Volvo seat

Klaus, I assume you are referring to the following procedure?
Self-Adjustment Of Damper Motor Limit Positions
1) Turn ignition on. Place fan (blower motor) lever in manual
mode. Turn function selector to AUT (automatic). Ensure system is in
TEST MODE 4.
2) Enter control code 9-9-9 by pressing button on diagnostic
unit 9 times in quick succession. Enter each of the 9 series 3 times,
with a short pause in-between to allow LED to come on again. ECC
control module is now ready to adjust damper motor limit positions
automatically.
3) Wait about 10 seconds for fan to start. Turn ignition off
to exit TEST MODE 4. Turn ignition on. AC OFF and REC indicator on A/C
control panel should flash. Drive car for a few minutes at speeds
greater than 20 MPH.
4) Stop car and turn engine off, but leave ignition on for at
least 2 minutes to enable ECC control module to store all values.
Start TEST MODE 1 and record DTCs. If DTC 1-1-1 appears, self-
adjustment is complete. If DTC 5-1-1 appears, self-adjustment is not
complete.
Changing Data Transmission Speed/Rate From ECC Control Module
To On-Board Diagnostic Unit
Enter desired control code (3-1-1 or 3-1-2) by pressing
button on diagnostic unit "A", with a short pause in-between to allow
LED to come on again. System always starts at normal speed unless
another option is selected. If another option was selected, system
will revert to normal speed each time ignition is turned off.

If you think the vents are being controlled properly and you get enough air flow, then 9-9-9 is not necessary. What it means at the end of the test is to turn off the engine but leave the key in position I for 2 minutes.

You will find that the test takes less than 1 mile at 25mph.
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My back feels better when I sit in a Volvo seat