Fans Not Working
10-28-2023, 03:49 PM
#16
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Alan
10-28-2023, 03:58 PM
#17
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As I am aware folks who carry out this kind of work warrant their efforts and a simple check with the supplier should help you clarify your position in that regard.
Duff motors can precipitate such failure but as you have new motors that seems unlikely. The mosfets will heat up during operation and if faulty that can cause them to take a dump until they cool down or so I would think.
10-28-2023, 04:10 PM
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Alan
10-28-2023, 04:24 PM
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Ash,
As I recall the switch closes at higher temperature so to simulate operation one has to short the two cables.
Check to ensure you see voltage on the feed cable to the PWM unit- if there is no voltage going in for sure non will be coming out.
The control unit next to the passenger seat sends a control signal to the PWM unit and both fans should run at the same speed. When the inlet manifold switch is made both fans should run at about 2//3rds of max speed. If the controller senses that both fans are not running it ramps up the operational fan to full speed.
The ac switch is used when testing because it turns on both fans at 2/3rds of max speed irrespective of engine temperature. When the ac is switched off the fans will not run until the requisite temperature in the water bride is reached and that is about 80C as i recall. The PWM unit is a solid state high frequency switching unit that turns power on/off rapidly - this simulates modulating the voltage and the fans operate as though they were being modulated by voltages in the range of 9V to 12 volts.
As I recall the switch closes at higher temperature so to simulate operation one has to short the two cables.
Check to ensure you see voltage on the feed cable to the PWM unit- if there is no voltage going in for sure non will be coming out.
The control unit next to the passenger seat sends a control signal to the PWM unit and both fans should run at the same speed. When the inlet manifold switch is made both fans should run at about 2//3rds of max speed. If the controller senses that both fans are not running it ramps up the operational fan to full speed.
The ac switch is used when testing because it turns on both fans at 2/3rds of max speed irrespective of engine temperature. When the ac is switched off the fans will not run until the requisite temperature in the water bride is reached and that is about 80C as i recall. The PWM unit is a solid state high frequency switching unit that turns power on/off rapidly - this simulates modulating the voltage and the fans operate as though they were being modulated by voltages in the range of 9V to 12 volts.
Hey Fred, What is the PWM unit?
10-28-2023, 04:59 PM
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Pulse width modulation unit. The fan controller unit sends it a signal telling it what is wanted and it responds accordingly by adjusting how long the voltage is applied relative to the time it is switched off. That is the unit on the front of the engine bay that is probably causing your grief.
10-29-2023, 11:54 AM
#22
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A MOSFET either works or dies - there is no coming back. Failures in the actual driver MOSFET are likely due to excess temperature or current (which amounts to excess temp pretty quickly). Most common causes on self rebuilds is insufficient cooling due to poor heatsink attachment (or poor thermal materials) or just incorrectly rated MOSFETs. If the pre-driver stage (sill area) fails such that it still works functionally but doesn't provide sufficient overdrive voltage for the MOSFET gates - this can also cause a driver stage voltage drop which will get you both lower fan speed operation and very rapid major driver stage overheating.
Alan
Alan
Not very well expressed by myself- these are rebuilt units and my thinking was more along the lines of a soldered joint failing thus rendering the mosfet [temporarily] inoperable and then operable upon cooling down a bit.
10-29-2023, 12:58 PM
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Alan
10-29-2023, 01:19 PM
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Swap the wires to the fans and see what happens - if the other fan now works and the previously working fan doesn't then the fans are both OK and the issue is upstream - in the fan controller, wiring, fuse etc. If the fan behavior stays the same (the same fan fails to work) then its a fan issue.
The relay has nothing to do with this (flaps only) so ignore that - but since something you did restored some function I'd be suspecting the fuses. You can test the fuses electrically and that is what you should do. On the face of the fuses (where the amperage rating is) there are 2 small dimples allowing you to probe the fuse blades while in circuit. Using a DVM ground one probe and test the voltage at the top of fuse #28 & #29 (for an '89). These are the inputs to the fuses (on '85 and later cars) you should have battery voltage there. Then test the bottom (output) of the fuse - you should also have battery voltage there. Try this again with the car running and the fans supposedly active - measure the bottom of the fuse - do both still have battery voltage. If yes to all then the fuses are OK and the fan amplifier looks more likely as a cause.
Alan
The relay has nothing to do with this (flaps only) so ignore that - but since something you did restored some function I'd be suspecting the fuses. You can test the fuses electrically and that is what you should do. On the face of the fuses (where the amperage rating is) there are 2 small dimples allowing you to probe the fuse blades while in circuit. Using a DVM ground one probe and test the voltage at the top of fuse #28 & #29 (for an '89). These are the inputs to the fuses (on '85 and later cars) you should have battery voltage there. Then test the bottom (output) of the fuse - you should also have battery voltage there. Try this again with the car running and the fans supposedly active - measure the bottom of the fuse - do both still have battery voltage. If yes to all then the fuses are OK and the fan amplifier looks more likely as a cause.
Alan
I checked the fuses and I DO NOT have 12V on one of the fuses. What is the process to correct this?
10-29-2023, 02:00 PM
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The fuse wasn't making good contact within that slot. I bent the blades a littel and now I get 12V on both. Both fans are working. Thanks for all the help guys.
Ash
Ash
10-29-2023, 03:21 PM
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I do agree that this suggests you will in fact have more fuse issues here in future. The likely problem is damage to the fuse holders. Most likely cause is poor quality fuses or water onto the panel from the blower motor area - evaluate visually for this. Use only good quality ATC/ATO fuses from Bussman or Littelfuse, these aren't really that expensive - and cheap Chinese fuses on eBay have very poor current accuracy ratings, the wrong plating materials and often dimensional problems with the blades. This can cause poor contact and high contact resistance @ the fuse connection - this then causes local heat and damage to: the fuse (melting), fuse holder (charred contacts) and overheated wire insulation on the CE panel wires - all bad news. If your fuses have bright brass/gold looking terminals - this is not good news (and not gold). But anyway if you don't know the provenance - it might be best to assume the worst
If the fuse holders (blocks of 5) are badly damaged they may need to be repaired (if possible) OR replaced with the exact same fuse block (matching numbers) - from the correct year of CE panel. They are NOT all the same - and the wrong ones can damage your car and cause all kinds of functional problems. From a donor panel you can also mix & match blocks and terminals in the holders to get what you need - they are differently connected inside on the input side. It is a fair amount of work to R&R these so if yours currently works - just use the proper high quality fuses.
Alan
If the fuse holders (blocks of 5) are badly damaged they may need to be repaired (if possible) OR replaced with the exact same fuse block (matching numbers) - from the correct year of CE panel. They are NOT all the same - and the wrong ones can damage your car and cause all kinds of functional problems. From a donor panel you can also mix & match blocks and terminals in the holders to get what you need - they are differently connected inside on the input side. It is a fair amount of work to R&R these so if yours currently works - just use the proper high quality fuses.
Alan
01-10-2024, 12:40 PM
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Hey guys,
still having issues with the fans. I decided to change the fan harness because only one fan worked sporadically. I changed the harness and neither fan works now. I tested the fuses (upper & lower) and I have 12-13 volts. When I shorted the wires on top of the intake, neither fan worked. I checked the voltage at the sensor on top of the intake and I’m getting nothing.
should I just get another sensor, or is there something or some connection I need to check first?
Ash
still having issues with the fans. I decided to change the fan harness because only one fan worked sporadically. I changed the harness and neither fan works now. I tested the fuses (upper & lower) and I have 12-13 volts. When I shorted the wires on top of the intake, neither fan worked. I checked the voltage at the sensor on top of the intake and I’m getting nothing.
should I just get another sensor, or is there something or some connection I need to check first?
Ash
01-10-2024, 02:34 PM
#30
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Ash,
Since you had issues occur before with the fuse holders I'd say its most likely still the cause here. Measuring 12v on the top and bottom blades of the fuse (in the dimples) doesn't mean for certain that the bottom blade is actually connecting to anything in the fuse holder. So an experiment here would be to test the pin out of the CE panel that connects to the bottom of these fuses. For fuse #28 its output goes out on CE Pin Q21 and Fuse #29 output goes out on CE Pin Q22 If this gives a different result than the bottom dimple of the associated fuse - your fuse holders are damaged enough they don't conduct.
Alan
Since you had issues occur before with the fuse holders I'd say its most likely still the cause here. Measuring 12v on the top and bottom blades of the fuse (in the dimples) doesn't mean for certain that the bottom blade is actually connecting to anything in the fuse holder. So an experiment here would be to test the pin out of the CE panel that connects to the bottom of these fuses. For fuse #28 its output goes out on CE Pin Q21 and Fuse #29 output goes out on CE Pin Q22 If this gives a different result than the bottom dimple of the associated fuse - your fuse holders are damaged enough they don't conduct.
Alan