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Need advice - 1990 760 ECC error code 233

There are three components in play. The control unit, a servo motor which is wired only to the control unit and a power unit wired directly to the blower fan and also connects to the low pressure switch on the accumulator. The control unit works the vents flawlessly. I centered around the power unit that feeds the blower fan. This is what I found. The BLK wire from the power unit is GND with no voltage variation when running. There is a GRN/YEL wire from the power unit to one side of the low pressure switch on the accumulator. The fan wiring is VIO and BLU/BLK. Weirdness: Both of these wires have the full BATT voltage when running and when the car is turned off! That ain't gonna run a fan! And, why are they powered when the car is turned off? Looking at the terrible schematic I have from my Haynes manual, the Control Unit feeds the input to the Darlington pair transistor via A RED/BLK wire. It looks like a relay in the power unit switches the output of one of the transistors to GND. The other output of the transistor is wired directly to the BLU/BLK fan wire. I can't really understand how it works from the schematic. Anyway I don't believe it is a bad control unit, because I have two and they both do exactly the same thing and issue the same error code (233). I did open them up and look for solder problems, but a close inspection didn't show any. I believe the problem could be the power unit and of course I can't find another one of those. I believe this is the case because I measured full battery voltage in respect to GND on both fan wires when the engine is running and the engine is off. That can't be right. I can run the fan by disconnecting the BLU/BLK wire from the power unit and grounding it. What is going on?
 
Mapleleafer said:
...suspect bad solder joints - although the transistor itself can fail.
Click to expand...

I remember chasing a similar problem on more than one 960 with ECC, and I remember the issues traced back to soldering. Well, actually not soldering, but delamination of the circuit board traces from the circuit board where the connector came in. Reflowing the solder solved the problem.

Now, which modules in the fan control system is lost in the pit I call my memory. I know I was put on to it by a post somewhere here, probably from before 2010. You might want to search "ECC bad solder" and see what it gets you.
 
jwernerny said:
I remember chasing a similar problem on more than one 960 with ECC, and I remember the issues traced back to soldering. Well, actually not soldering, but delamination of the circuit board traces from the circuit board where the connector came in. Reflowing the solder solved the problem.

Now, which modules in the fan control system is lost in the pit I call my memory. I know I was put on to it by a post somewhere here, probably from before 2010. You might want to search "ECC bad solder" and see what it gets you.
Click to expand...

Man I am good. Found a thread about it (from 2006!): http://forums.turbobricks.com/showthread.php?t=73422&highlight=solder
 
jwernerny said:
Man I am good. Found a thread about it (from 2006!): http://forums.turbobricks.com/showthread.php?t=73422&highlight=solder
Click to expand...

Thanks for the link cjwernemy. I think it addresses a different problem than I'm having. My control unit(s) switch between the vents properly. As I mentioned previously, in the winter I hooked up a mechanical switch and a resistor array to bypass the control unit and run this car's original fan at three speeds. The control unit worked perfectly for heat control and vent switching. I could direct the heat to the floor, dash vents or defrost vents at will. Now that summer's here, I need air conditioning, so I went back to the factory system. Re-soldering seem to be the default advice for Volvo circuit boards and relays. I wish it were that simple. I am leaning toward replacing the power unit since that's the only part of the system I cannot verify. I'll start hitting the junk yards hoping to find one.
 
ZVOLV said:
Do voltage drop tests.
Click to expand...

I did a voltage drop test between the ground wire on the power unit ground lead and chassis ground. There was no detectable voltage difference with the engine running. I'm not sure where else I should test. But the problem as I see it now is that 12V (14V with engine running) appears on both sides of the two-wire connection to the blower fan. I don't get it. For safety, I disconnected one wire (blu/blk) from the power unit and grounded it. The fan spun immediately but I didn't want to run it for too long since there was no resistance in the path. This can't be right and I don't know how a voltage drop test would help here. I'm guessing defective transistor amplifier in the power unit. I wish I had an easier-to-read schematic, like the ones you see in the green books. Does anyone have one?
 
Mapleleafer said:
A bad ground will reduce the current draw across the motor. That said, I found the wiring diagram and see that the motor ground circuit includes a common ground for the dash (control) unit, making it lower on the list. That makes bad solder in the module my #1 suspicion (like every other Volvo module, controller relay or gauge that I've seen which doesn't work correctly). Resolder the 2 pins at the transistor itself, and all the ones where the plug connector meets the PC board. If solder does not cure the error code, the transistor has failed.

Here is a list of the wire functions:
Heavy wires
1 VIO fused power from battery
1A BL-BK neg side of blower motor
2A BK Ground

Smaller wires
2 GN-Y to A/C compressor low pressure switch
3 BL-R hi blower relay coil
4 PK PWM blower speed signel (transistor B)
5 BN A/C compressor relay coil
6 PK blower current sense
Click to expand...

I wonder if I inserted a resistor in series with the pink wire would it reduce the current and fool the control unit?
 
missthe1122 said:
I did a voltage drop test between the ground wire on the power unit ground lead and chassis ground. There was no detectable voltage difference with the engine running. I'm not sure where else I should test. But the problem as I see it now is that 12V (14V with engine running) appears on both sides of the two-wire connection to the blower fan. I don't get it. For safety, I disconnected one wire (blu/blk) from the power unit and grounded it. The fan spun immediately but I didn't want to run it for too long since there was no resistance in the path. This can't be right and I don't know how a voltage drop test would help here. I'm guessing defective transistor amplifier in the power unit. I wish I had an easier-to-read schematic, like the ones you see in the green books. Does anyone have one?
Click to expand...

Two things;
1- I mistakenly wrote pink for pin 4 instead of red/black and 2, you overlooked my original reply that mentions that the control circuit is on the ground side of the motor.
This means that without any current flow to run the motor, having full battery voltage on both sides is absolutely correct. The transistor is there to provide speeds less than maximum. Full speed is accomplished by engaging a relay whose contacts bypass the transistor and tie the heavy blue/black terminal directly to ground, just as you did with the jumper wire.

Current sensing works by looking for the voltage differential between the pink and red/black wires. It should probably be somewhere between 0.6 and 1.3 volts, depending on speed and whether the motor is accelerating or stabilized. As all current sensing circuits do, it is measuring a voltage drop across two points with known characteristics. Georg Ohm did a really good job of explaining this phenomena.

The place to look for bad solder is INSIDE the power module at the transistor pins, and the blades to the wire connectors. I'm fairly sure that the same part was used from 1988 to 1998 on 760,780, 960, 940SE, V/S90.
 
lummert said:
Question about the blower current sense wire. How many volts should be going to this using a resistor? I don't need to worry about my a/c as the compressor is no longer in place seeing as the a/c hasn't worked for as long as I've owned the car (13 years).
Click to expand...

I'm thinking that it measures current flow rather than voltage. I'm going to try inserting a resistor in series with the wire starting with a low ohm value to see if reduced current clears the error message and allows the fan to run. If this works you should be able to eliminate the switch you rigged up and use the control unit to run the fan. I had a 960 with a crappy compressor (no AC) but the control unit still ran the fan for heat and defrost.
 
Mapleleafer said:
Two things;
1- I mistakenly wrote pink for pin 4 instead of red/black and 2, you overlooked my original reply that mentions that the control circuit is on the ground side of the motor.
This means that without any current flow to run the motor, having full battery voltage on both sides is absolutely correct. The transistor is there to provide speeds less than maximum. Full speed is accomplished by engaging a relay whose contacts bypass the transistor and tie the heavy blue/black terminal directly to ground, just as you did with the jumper wire.

Current sensing works by looking for the voltage differential between the pink and red/black wires. It should probably be somewhere between 0.6 and 1.3 volts, depending on speed and whether the motor is accelerating or stabilized. As all current sensing circuits do, it is measuring a voltage drop across two points with known characteristics. Georg Ohm did a really good job of explaining this phenomena.

The place to look for bad solder is INSIDE the power module at the transistor pins, and the blades to the wire connectors. I'm fairly sure that the same part was used from 1988 to 1998 on 760,780, 960, 940SE, V/S90.
Click to expand...

Okay. I wasn't sure how the current sensing worked. And the full voltage on both sides now makes sense. I really appreciate your input. My electronics knowledge is limited. It's kind of tricky to remove the power module, but I'll try exactly what you've said. Thanks again!!!
 
I removed the power stage and re-soldered the three pins of the transistor. The center pin solder looked a little fishy. Re-connected it and of course the same 233 and no fan. I'll be calling junkyards again after Memorial Day. I'd like to buy another power stage to see what happens. If anyone has one please let me know.
 
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