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Blower Power Transistor

Awesome posts! Think I'll be able to get to the bottom of my AC gremlins. So just to clarify, if your fan only works when the fan speed knob is turned to HIGH, the issue is with the CCU, and related generally to bad caps and busted traces. But if the fan only blows high, regardless of what position the fan speed knob is turned to, then the issue is likely a blown transistor that's not modulating the speed of the fan. Am I good so far?

Is it possible for the transistor to work intermittently? Symptoms of my AC are:
- fan blows on balls-out high speed 98% of the time, regardless of where the fan speed knob is turned to. The other 2% of the time, the motor speed slows for 5-30 seconds to what I'm assuming is the correct speed, given that the cabin has cooled down to ~around the correct temperature (I'm guessing). But then it goes back to blowing at max speed.
- Also, hitting the Off button on the CCU will shut the display down, but the fan motor will continue to blow.

If the issue ends up being the transistor assembly, I'd like to at least make a go at fixing it. Obvious step would be to replace transistor (2SD1460/MJ 11016). Then, 2 questions:
- If it turns out that the thermal fuse is blown as well, would y'all happen to have a part # for the replacement?
- Can the blower motor be opened up? If so, shouldn't be too hard to clean some of the oxidation off the commutator.

Thanks a ton, guys!
 
NSteX said:
Awesome posts! Think I'll be able to get to the bottom of my AC gremlins. So just to clarify, if your fan only works when the fan speed knob is turned to HIGH, the issue is with the CCU, and related generally to bad caps and busted traces. But if the fan only blows high, regardless of what position the fan speed knob is turned to, then the issue is likely a blown transistor that's not modulating the speed of the fan. Am I good so far?

Is it possible for the transistor to work intermittently? Symptoms of my AC are:
- fan blows on balls-out high speed 98% of the time, regardless of where the fan speed knob is turned to. The other 2% of the time, the motor speed slows for 5-30 seconds to what I'm assuming is the correct speed, given that the cabin has cooled down to ~around the correct temperature (I'm guessing). But then it goes back to blowing at max speed.
- Also, hitting the Off button on the CCU will shut the display down, but the fan motor will continue to blow.

If the issue ends up being the transistor assembly, I'd like to at least make a go at fixing it. Obvious step would be to replace transistor (2SD1460/MJ 11016). Then, 2 questions:
- If it turns out that the thermal fuse is blown as well, would y'all happen to have a part # for the replacement?
- Can the blower motor be opened up? If so, shouldn't be too hard to clean some of the oxidation off the commutator.

Thanks a ton, guys!
Click to expand...

All the climate control units fail so if yours has not been rebuilt I would start with that. It also sounds like your blower high relay is sticking on, those like to melt and fail.
 
Thanks Brian! Hadn't even heard of the blower high relay. Found it in the manual (RTFM, right?).

Actually, started with a rebuild of the CCU (caps/traces), and that cured the initial issue of fan only working when knob was turned to "high" and the issue of the unit intermittently turning off.

Will report back. Thanks again.

- - - Updated - - -

Thinking about it more, what causes the relay to melt, do you think? High current draw from a dirty blower motor?
 
The relay caries a lot of current and sometimes they get hot and melt, just the nature of the design of car electricials.


NSteX said:
Thanks Brian! Hadn't even heard of the blower high relay. Found it in the manual (RTFM, right?).

Actually, started with a rebuild of the CCU (caps/traces), and that cured the initial issue of fan only working when knob was turned to "high" and the issue of the unit intermittently turning off.

Will report back. Thanks again.

- - - Updated - - -

Thinking about it more, what causes the relay to melt, do you think? High current draw from a dirty blower motor?
Click to expand...
 
daveh said:
just as ibadnsx and brian k said the transistor does get bypassed when on hi only and the resistance in the blower motor is usually always the cause either do to debris or dust/dirt causing drag on the bearings.If your buddy who lent you the control head still has his car it only takes about 5 minutes to switch out the transistor.good luck
Click to expand...

Briank said:
The relay caries a lot of current and sometimes they get hot and melt, just the nature of the design of car electricials.
Click to expand...

Briank looked at my board and I'm 99% sure the transistor needs to be replaced. Yes it's 2 bolts but how in the world did you get to the back Phillips screw in 5 minutes?
 
With CCU removed or plugged in (just back from rebuild) fan is still blowing on max all the time.
Removing the relay on the right fan stops blowing. I assume it is the main blower relay.
Another posted indicated Blower Hi Relay is next to it (and they are known to get stuck). But removing it does NOT stop the fan (CCU in or out).

https://www.dropbox.com/s/tooq0zdqm2ult2m/IMG_8686b.jpg?dl=0

Is the power transistor shorted, providing ground to the blower motor and causing it to run on high?

Where is the power transistor located (1991)? Links/DIY how to remove it?
 
You need to figure out what relay you are pulling to stop the blower motor, blower relay or the blower high relay. power transistors normally fail open so its unlikely its shorted.





KraftwerkTurbo said:
With CCU removed or plugged in (just back from rebuild) fan is still blowing on max all the time.
Removing the relay on the right fan stops blowing. I assume it is the main blower relay.
Another posted indicated Blower Hi Relay is next to it (and they are known to get stuck). But removing it does NOT stop the fan (CCU in or out).

https://www.dropbox.com/s/tooq0zdqm2ult2m/IMG_8686b.jpg?dl=0

Is the power transistor shorted, providing ground to the blower motor and causing it to run on high?

Where is the power transistor located (1991)? Links/DIY how to remove it?
Click to expand...
 
Last edited:
You can set up to test the transistor if you are handy with electronics and have the 'stuff' to do the test. You can also buy dedicated transistor checkers or if you go to an electronics parts vendor, they may have a tester that they could use to do a test on the transistor. Doing a static test with a multimeter is problematic.

The blower power transistor module is not cheap. Before you order a new one pull the module and wiring out and carefully examine the wires at the plug end of the wiring harness and where the wiring enters the transistor module. Look for frayed wiring that may have shorted out. As Brian K. noted, its more common for transistors to fail open rather than short out like yours appears to have done. If there is an external short in the wiring you might be able to repair it.
 
Old Guy said:
You can set up to test the transistor if you are handy with electronics and have the 'stuff' to do the test. You can also buy dedicated transistor checkers or if you go to an electronics parts vendor, they may have a tester that they could use to do a test on the transistor. Doing a static test with a multimeter is problematic.

The blower power transistor module is not cheap. Before you order a new one pull the module and wiring out and carefully examine the wires at the plug end of the wiring harness and where the wiring enters the transistor module. Look for frayed wiring that may have shorted out. As Brian K. noted, its more common for transistors to fail open rather than short out like yours appears to have done. If there is an external short in the wiring you might be able to repair it.
Click to expand...

Transistor and wires appear to be new.
I suspect previous owner bought new power transistor module including harness. Too lazy to install, and just zip tied to driver side loom.

I have a 'brother' (manual) 1991 car accessible. Is there a risk of swapping the transistor module over for test purposes? Unfortunately, this won't be a definitive test, since this one ALSO has HVAC/module/blower/power transistor/relay issues (was next on my list to fix once this (automatic) is done.

But I would swap in (if no risk): if it RUNS, then bad transistor module. If NOT, search continues for cause of high speed fan running max all the time.

Still would like to know where the 2 fan modules are located (particularly the HI).
 
KraftwerkTurbo said:
Transistor and wires appear to be new.
I suspect previous owner bought new power transistor module including harness. Too lazy to install, and just zip tied to driver side loom.

I have a 'brother' (manual) 1991 car accessible. Is there a risk of swapping the transistor module over for test purposes? Unfortunately, this won't be a definitive test, since this one ALSO has HVAC/module/blower/power transistor/relay issues (was next on my list to fix once this (automatic) is done.

But I would swap in (if no risk): if it RUNS, then bad transistor module. If NOT, search continues for cause of high speed fan running max all the time.

Still would like to know where the 2 fan modules are located (particularly the HI).
Click to expand...

The transistor module is installed in the blower housing so that it gets forced air cooling. If it was left just hanging in the front compartment, it may have overheated resulting in its failure.

Others can confirm; but, I believe that the power transistor module stayed the same right through to the final production year. The modules will likely have part numbers on them and the same part number would confirm that they are inter changeable.

Fan modules? Do you mean the relays? On a 1991 car the Blower Relay is the one in the photo that you posted with the red arrow and the Blower Hi Relay is the one right beside it.
 
Old Guy said:
Fan modules? Do you mean the relays? On a 1991 car the Blower Relay is the one in the photo that you posted with the red arrow and the Blower Hi Relay is the one right beside it.
Click to expand...

Yes, fan relays. Thanks for confirming positions. Will swap them with others of the same type to test functionality, just to be sure.

Here are photos of the power transistor (I think it looks fairly new; and was NOT installed in the fan housing as I mentioned above; hence my assumption that it was changed, and lazy mechanic just zip tied it on):
https://www.dropbox.com/s/mm0yhwo6gpprwra/IMG_8728.JPG?dl=0\
https://www.dropbox.com/s/96jgj11pfdefule/IMG_8730.JPG?dl=0
https://www.dropbox.com/s/eb8jlsfl6jm2zcg/IMG_8731.JPG?dl=0
https://www.dropbox.com/s/26s78xv2j76io66/IMG_8732.JPG?dl=0
https://www.dropbox.com/s/6vmz0v5lpdjcvza/IMG_8733.JPG?dl=0
 
BTW: the 'brother' car (manual instead of auto) shows the same symptoms: only blowing high. Plan was to take CCU out and mail in for repair. But in light of what is going on with this one, will first figure out what is causing the 'blow on high'.
Can someone confirm that:
a) with CCU disconnected, fan should not blow (certainly not on high)
b) with HI fan relay removed, fan should not blow on high
c) with power transistor unplugged, fan should not run on high, unless CCU is turned to high and closes HI relay
 
KraftwerkTurbo said:
BTW: the 'brother' car (manual instead of auto) shows the same symptoms: only blowing high. Plan was to take CCU out and mail in for repair. But in light of what is going on with this one, will first figure out what is causing the 'blow on high'.
Can someone confirm that:
a) with CCU disconnected, fan should not blow (certainly not on high)
b) with HI fan relay removed, fan should not blow on high
c) with power transistor unplugged, fan should not run on high, unless CCU is turned to high and closes HI relay
Click to expand...

a) - correct
b) - correct (definitely if the CCU is disconnected. If the CCU is connected the CCU might continue to apply a control signal to the base of the transistor causing it to continue to switch at the speed just below high. I have never investigated to confirm whether the control signal to the transistor is supressed when the fan speed is switched to high)
c) - correct
 
Last edited:
Relays tested (both HI and fan power).
New transistor installed. Repaired (came with car, not installed) CCU plugged in. Now runs.
It appears the cooling fins of the transistor CANNOT touch metal/ground. This may have been the issue on this car. Previous owner cut connector to installed transistor, and zip tied new transistor to AC lines under hood.

I got the old transistor out (and new one installed into the blower box).

I would like to repair the old transistor. Any photos or DIY link how the dig up the transistor (dremel), remove and install new transistor?
 
Briank said:
The transistor needs to be mounted in the blower assy for cooling.
Click to expand...
I put the new power transistor into the blower box where it belongs. But what a PITA that was. The rear philips is very difficult to get out and in.
And the unit does not want to come easily, blocked by the heater pipes; I could not get the rear hose of the hard line (did not want to risk ripping it). Removed two top screws of the box, allowed enough moved to force old unit out and new in.

Another reason it is NOT a good idea to just leave the transistor in the bay: when backside fins/housing connect with metal, it grounds the transistor, makes it run on high. When I found it that way, unit was VERY hot (thought it shorted, but likely hot from running on high).
 

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