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Old 05-17-2019, 01:50 PM   #1
missthe1122
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Default Need advice - 1990 760 ECC error code 233

I'm trying to get my ECC system to work, but I get the flashing AC button and no fan function. The diagnostics test issues error code 233 Fan motor excessive starting current. This is the only error code present. In the winter I rigged up a manual switch + resistor pack to run the fan for heat and defrost function. This worked just fine, providing 3 fan speeds no problem. Now I need AC, so I bought a new VDO blower fan in case the old fan was actually "drawing too much current" but I get the same error code. I also swapped out the ECC control unit with another known good one and I got the same 233 error code. What's strange is when I first installed the new fan, the fan switch ran the fan at all the speeds. I thought my problems were over, but it hasn't worked since the initial try, and as soon as I turn the switch from AUT or 0 position, the AC button begins to flash. FYI I can trigger the AC compressor clutch by jumping 12V to the output side of the AC pressure switch but there is no voltage on the other terminal of the AC pressure switch. I read the article about converting from MCC to ECC and I noticed "ECC is not only more sophisticated and advanced, it can also be controlled manually just like MCC if you don’t like what the computer is doing." How do you do make this happen? My thought is if I can't figure out the excessive starting voltage problem, I would try to re-wire the system to bypass the control unit and convert the system to MCC. Not sure what to do at this point. Any suggestions?
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Old 05-17-2019, 02:05 PM   #2
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I always do blowers and resistors as a pair. The blower gets old and starts pulling too much current and fries the resistor.
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Old 05-17-2019, 02:25 PM   #3
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Originally Posted by missthe1122 View Post
I'm trying to get my ECC system to work, but I get the flashing AC button and no fan function. The diagnostics test issues error code 233 Fan motor excessive starting current. This is the only error code present. In the winter I rigged up a manual switch + resistor pack to run the fan for heat and defrost function. This worked just fine, providing 3 fan speeds no problem. Now I need AC, so I bought a new VDO blower fan in case the old fan was actually "drawing too much current" but I get the same error code. I also swapped out the ECC control unit with another known good one and I got the same 233 error code. What's strange is when I first installed the new fan, the fan switch ran the fan at all the speeds. I thought my problems were over, but it hasn't worked since the initial try, and as soon as I turn the switch from AUT or 0 position, the AC button begins to flash. FYI I can trigger the AC compressor clutch by jumping 12V to the output side of the AC pressure switch but there is no voltage on the other terminal of the AC pressure switch. I read the article about converting from MCC to ECC and I noticed "ECC is not only more sophisticated and advanced, it can also be controlled manually just like MCC if you don’t like what the computer is doing." How do you do make this happen? My thought is if I can't figure out the excessive starting voltage problem, I would try to re-wire the system to bypass the control unit and convert the system to MCC. Not sure what to do at this point. Any suggestions?
The panel in the dash indirectly controls the fan. There is a control unit mounted to the heat/AC case just to the right of the transmission tunnel. Usually when you are getting no blower, or, that code, the control unit is the problem. This controller also switches all the vacuum actuators.
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Old 05-17-2019, 02:59 PM   #4
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I always do blowers and resistors as a pair. The blower gets old and starts pulling too much current and fries the resistor.
This car uses a different system than the MCC. Instead of a resistor pack , the output to the blower comes from a servo motor??? Whatever that is. It's near impossible to find that unit. I have a manual switch and a resistor pack from a chevy which I used in the winter to run the fan at 3 speeds. I powered it via a fused 30A line switched via a relay. It worked fine for the heat and defrost. But now I want to get the AC going. I installed a brand-new VDO blower fan so it shouldn't draw too much current. I could put the resistors and switch back in but I'm not sure how to wire the AC. I was going to go directly to the compressor but someone said without pressure control, I'd blow up the system. I'm wondering could I just put 12V to the input side of the pressure switch on the AC dryer?
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Old 05-17-2019, 03:05 PM   #5
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The panel in the dash indirectly controls the fan. There is a control unit mounted to the heat/AC case just to the right of the transmission tunnel. Usually when you are getting no blower, or, that code, the control unit is the problem. This controller also switches all the vacuum actuators.
I thought about that unit. The vacuum actuators work because I can switch between vents and it did run the fan at all 4 speeds the first time I turned it on. I'm wondering what the controller uses to sense "too much starting current" maybe I can "trick" the controller that way. That servo unit is impossible to find. I've tried. I know the 960 used the same system, but there are not many junked 760's or 960's around here.
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Old 05-19-2019, 09:43 AM   #6
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I thought about that unit. The vacuum actuators work because I can switch between vents and it did run the fan at all 4 speeds the first time I turned it on. I'm wondering what the controller uses to sense "too much starting current" maybe I can "trick" the controller that way. That servo unit is impossible to find. I've tried. I know the 960 used the same system, but there are not many junked 760's or 960's around here.
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Old 05-19-2019, 03:19 PM   #7
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Put ad on the wanted section, someone will have one.
I'm not confident that the servo control is the problem and I don't want to wait weeks to find out. I'd rather just bypass the ECC system entirely and activate the AC manually. I'd appreciate advice on how to do that. I already have the parts to hook up the blower fan. I just need to know how to wire the AC system to safely trigger the compressor. I was thinking that I could just run 12V to one side of the low pressure switch since the other side goes directly to the compressor, but I don't know too much about Volvo AC systems.
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Old 05-20-2019, 10:34 AM   #8
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There is a Darlington power transistor module mounted near the blower. This allows a low current signal from the dash unit to control the high current to the motor. Opposite of many control devices; the motor is powered directly from the fuse and the power control is on the ground side. Part of this module is a low value resistor used for current sensing. One of the two small wires is the control wire to the base of the transistor, the other is the current sense output back to the dash unit.

First, disable your added stuff to put the system back the way it was. Then backprobe the heavy black wire of the power module with a voltmeter and connect its other end to a known good ground. Ignition on and read the meter when you turn the fan selector to 1. If you see it rise to more than 0.1 volts, you have a bad ground to the module. And if this low setting is enough to trigger the error, the failure is inside the module - suspect bad solder joints - although the transistor itself can fail.

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Old 05-20-2019, 02:21 PM   #9
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^^^The voltage drop test is a good idea. You could also use a current clamp and do some tests.
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Old 05-20-2019, 02:38 PM   #10
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Originally Posted by Mapleleafer View Post
There is a Darlington power transistor module mounted near the blower. This allows a low current signal from the dash unit to control the high current to the motor. Opposite of many control devices; the motor is powered directly from the fuse and the power control is on the ground side. Part of this module is a low value resistor used for current sensing. One of the two small wires is the control wire to the base of the transistor, the other is the current sense output back to the dash unit.

First, disable your added stuff to put the system back the way it was. Then backprobe the heavy black wire of the power module with a voltmeter and connect its other end to a known good ground. Ignition on and read the meter when you turn the fan selector to 1. If you see it rise to more than 0.1 volts, you have a bad ground to the module. And if this low setting is enough to trigger the error, the failure is inside the module - suspect bad solder joints - although the transistor itself can fail.
This sounds like a good way to move forward. Thank you for the explanation. I've already returned the system to factory and installed a brand-new blower fan. I see the module where the fan wires are attached to. I was beginning to suspect a bad ground, but your test is very explicit. I'll try it and report the results. Apparently error code 233 is fairly common, but the advice I found so far just says replace parts. I prefer troubleshooting as you've described.
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Old 05-20-2019, 06:27 PM   #11
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I replaced the blower motor on my 88 765 before figuring out that there was nothing wrong with the original. I ran a switch to a radiator cooling fan ballast resistor and a ground wire to the blower motor. I found the wiring points needed on the rear of the relay panel. there is a ground point on the trans tunnel in back of the relay panel. Relay panel is on passenger side behind the radio console.
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Old 05-20-2019, 06:38 PM   #12
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^^^The voltage drop test is a good idea. You could also use a current clamp and do some tests.
Original poster said he already replaced the motor with new and got the same result. That is practically a guarantee that there is not excessive current draw. This is a sensing issue.
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Old Yesterday, 03:27 PM   #13
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Originally Posted by Mapleleafer View Post
Original poster said he already replaced the motor with new and got the same result. That is practically a guarantee that there is not excessive current draw. This is a sensing issue.
I thought the same thing, but a voltage test is valid. A bad ground could cause excessive current draw even with a new replacement. I have two control units and they both issue the same error code. It's hard to believe that I have two control units failing in the same way - especially since one of them was working in the car I removed it from. I really want this mystery solved, so I'll try all the advice I receive. Thanks to all for the assistance.
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Old Yesterday, 03:32 PM   #14
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Originally Posted by Mapleleafer View Post
Original poster said he already replaced the motor with new and got the same result. That is practically a guarantee that there is not excessive current draw. This is a sensing issue.
Following another post, I installed a mechanical switch and a resistor array, which gave me 3 fan speeds using the original fan so I could have heat in the winter. Now I want AC and would like to get the original factory setup working. I'll just keep trying to figure this one out. I know you recommended using a chevy blower motor, but I purchased an original replacement made by VDO expecting that to work. So far it returned me to my original problem.
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Old Yesterday, 03:33 PM   #15
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Originally Posted by lummert View Post
I replaced the blower motor on my 88 765 before figuring out that there was nothing wrong with the original. I ran a switch to a radiator cooling fan ballast resistor and a ground wire to the blower motor. I found the wiring points needed on the rear of the relay panel. there is a ground point on the trans tunnel in back of the relay panel. Relay panel is on passenger side behind the radio console.
Following you advice from another post, I installed a mechanical switch and a resistor array, which gave me 3 fan speeds using the original fan so I could have heat in the winter. Now I want AC and would like to get the original factory setup working. I'll just keep trying to figure this one out. I know you recommended using a chevy blower motor, but I purchased an original replacement made by VDO expecting that to work. So far it returned me to my original problem.
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Old Yesterday, 04:38 PM   #16
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Originally Posted by missthe1122 View Post
I thought the same thing, but a voltage test is valid. A bad ground could cause excessive current draw even with a new replacement. I have two control units and they both issue the same error code. It's hard to believe that I have two control units failing in the same way - especially since one of them was working in the car I removed it from. I really want this mystery solved, so I'll try all the advice I receive. Thanks to all for the assistance.
What do you mean when you say control units? The panel in the dash with the temperature and fan speed control on it, or, the vacuum solenoid control unit?
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Old Yesterday, 09:25 PM   #17
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Quote:
Originally Posted by missthe1122 View Post
I thought the same thing, but a voltage test is valid. A bad ground could cause excessive current draw even with a new replacement. I have two control units and they both issue the same error code. It's hard to believe that I have two control units failing in the same way - especially since one of them was working in the car I removed it from. I really want this mystery solved, so I'll try all the advice I receive. Thanks to all for the assistance.
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
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