Volvo 850 ECC Testing/faulty?

[abscate]

Do you think everyone at ALPS has headed for the mountains?

[Palou]

Hello,
I love my beautiful 1994 Volvo 850 2,4L non turbo station wagon.
Same as Navy, I got 3 years later the same dtc 419 with blower not activated by the ECC, nor by the rheostat sliding knob.
The blower itself works when blue line is jumpered to ground.
As suggested by dtc 419 trouble shooting, manual, I have checked the ground circuits.
The black wire from pin A6 was the only one connected to ground,
The 3 other brown wires from pin A9, A10 and C10 (=56 on test unit) were not connected to ground as expected and them are not connected between them.
On the A/C system wiring diagram these brown wires appear as being connected but I was unable to discover after tracking where was located their common ground connection which I presumed as being faulty.
I went extensively throughout MVS and web litterature, no way to find an answer.
Has anyone an idea about how and where these 3 brown wires are physically connected together and to ground as described on the wiring diagramm.

The ohmmeter did not confirm that these 3 brown wires are connected between them.

On another hand, the 3 wires connected to the power stage show continuity from pin A5, A27 and B12 (=42 on test unit) up to their terminal on the power stage.
The other A/C équipements (sensors, dampers, compressor, …) are operational
The blower stopped to be operational alter I disconnected the battery for one night.
I présume however that the ground circuit défault has to be settled first before considering any problem with the power stage itself.
Thanks in anticipation for your help.

[jreed]

I'm not sure this will be of any use to you, and you may have already seen it, but there is some description here of how to test for DTC 419:

Volvo 850 ECC climate control AC & heater system service manual.pdf

(1.3 MiB) Downloaded 103 times

"DTC 4-1-9 ECC POWER STAGE EMITTING FAULTY DIAGNOSTIC SIGNAL
1) Ensure ignition is off. Connect test unit to ECC control module. Check ground circuits. See DTC 1-2-1, OUTSIDE TEMP. SENSOR CIRCUIT SHORTED TO GROUND. If ground circuits are okay, go to next step.
2) Turn ignition on. Connect voltmeter between test unit pins
No. 6 and 27. Voltmeter should indicate 3 volts. If voltmeter
indicates one volt, there is no control signal to power stage. See DTC
4-1-8, NO CONTROL SIGNAL TO ECC POWER STAGE. If voltmeter indicates 4 volts, there is excessive voltage from power stage. See DTC 4-1-1, PASSENGER COMPARTMENT FAN OVERCURRENT OR SEIZED FAN.
3) If voltmeter indicates 12 volts, check wire at ECC control module terminal A27 (Violet/White wire) for a short to voltage. See Fig. 10. If voltmeter indicates zero volts, wire has an open circuit
or is shorted to ground. Go to next step.
4) Ensure ignition is off. Disconnect power stage 4-pin connector. See Figs. 14 and 15. Check Violet/White wire between power stage connector terminal 2A and ECC control module terminal A27 for a short to ground or open circuit. If wire is okay, go to next step.
5) Reconnect power stage 4-pin connector. Turn ignition on. Connect voltmeter between test unit pins No. 6 and 5. If battery voltage is present, go to next step. If zero volts are present, wire is shorted to ground.
6) Ensure ignition is off. Disconnect power stage 4-pin connector. Connect ohmmeter between test unit pin No. 5 and power
stage connector terminal 3A. If ohmmeter indicates continuity, replace power stage. If ohmmeter indicates no continuity, check wiring for an open circuit and repair as necessary.

[Palou]

Thanks JReed,
I was stuck with step 1) and the ground problem
Today I discovered where 10 brown wires are joining in the harness bearing the blower motor.
I then probably shaked some wires and found that the brown wires were connected to ground (apparentai by the ECC and not by a connexion direct to the car body)
However the blower did not restart.
I know have to understand why (step 2/3) there is 0 volt between wires from pins A6 and A27 although they are neither open nor shorted to ground.
The only odd connexion I discovered by testing was that the pink wire connected to pin A3 (going to interior lights system) is full contact with ground A6.
I am elsewhere wandering if the heather fan relay located above the engine radiator may be the cause of à default for the blower which does not work in the cabin.
I have now the engine warning light (with the lambda sign) which has lighted on and I wonder if problems are related.

Last, I have to look for how to check the power stage and fix it whenever possible..

Thanks for any help.
I already spent hours and days during last 12 months trying to repair my A/C automatic system while it is now very hot outside.