Climate Control Fan Speed
01-16-08, 05:05 PM
#32
as an electrical junkie maybe i can shed some light here.
power resistors do not "go bad" very easily.
It is the strongest part in the circuit.
the transistor is probably your culprit, and 99% cannot be repaired.
you need to replace it and depending on the specs you might be able to get an aftermarket one, since its toyota I would imagine the connector is diff at the least.
signs of a transistor not properly switching is a buzzing sound, and in much worse cases a ticking sound.
A bad transistor should be replaced very soon or at the least be removed to protect other electrical components on the same line from shorting out.
If the transistor goes AWOL and starts rapidly switching from power to ground it could ruin the resistor and melt wires and etc etc. you get my point.
unlikely? yes.
impossible? no
power resistors do not "go bad" very easily.
It is the strongest part in the circuit.
the transistor is probably your culprit, and 99% cannot be repaired.
you need to replace it and depending on the specs you might be able to get an aftermarket one, since its toyota I would imagine the connector is diff at the least.
signs of a transistor not properly switching is a buzzing sound, and in much worse cases a ticking sound.
A bad transistor should be replaced very soon or at the least be removed to protect other electrical components on the same line from shorting out.
If the transistor goes AWOL and starts rapidly switching from power to ground it could ruin the resistor and melt wires and etc etc. you get my point.
unlikely? yes.
impossible? no
01-16-08, 05:25 PM
#33
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In the case of the blower motor the resistor appears to fail closed and does not flap or do anything else.
It just supplies full power to the motor. I guess this is preferable to failing open and therefore no power.
In my experience the resistor packs often fail, transistors seem to be more reliable from what I have seen.
Matt.
It just supplies full power to the motor. I guess this is preferable to failing open and therefore no power.
In my experience the resistor packs often fail, transistors seem to be more reliable from what I have seen.
Matt.
01-16-08, 05:59 PM
#34
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I am installing mine tomorrow morning and I will try to post pics. This is one of downsides of owning an older car. Problems like this dont affect the performance of the car but can wear you down.
01-16-08, 06:04 PM
#35
In the case of the blower motor the resistor appears to fail closed and does not flap or do anything else.
It just supplies full power to the motor. I guess this is preferable to failing open and therefore no power.
In my experience the resistor packs often fail, transistors seem to be more reliable from what I have seen.
Matt.
It just supplies full power to the motor. I guess this is preferable to failing open and therefore no power.
In my experience the resistor packs often fail, transistors seem to be more reliable from what I have seen.
Matt.
one would be an open circuit where the resistance is so high that it will not allow any current to flow across it. If your AC still works this is not the case.
the second is a closed or "short" circuit where there is effectively no resistance any more and current is free to flow.
This is the only possible scenario that could happen here and this only happens from an intense heat buildup most common to another component that has failed, ie your transistor.
The resistor has nothing to do with how fast your fan blows, that is entirely dependent on the switching rate of the transistor at that resistance level.
when the transistor stops switching you get full fan speed because its running at 100% duty cycle (which should never happen even at full fan speed!). you could imagine that when it is stuck here this can cause alot of strain on the system and blow some resistors.
Think of it like what happens when you run your injectors at 100% duty cycle all the time. something has got to give.
if its broken then take it out asap, better safe than sorry.
thats all i'm trying to say
see wiki here: http://en.wikipedia.org/wiki/Pulse-width_modulation
01-16-08, 06:14 PM
#36
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Thanks for the info.
I haven't seen a wiring diagram for the blower motor assembly so I am not 100% sure how it is setup however commonly the resistor pack is used to provide variable fan speed and a transistor module is used in place of a relay to provide full power.
It might well be different on the Lexus with the resistor pack working with the transistor module, I couldn't say. As they are two separate modules I would assume that they aren't directly related, however you know what they saw about assumption :-)
The working diagram I saw had the resistor pack located in the airstream of the fan assembly which is usually done to cool the resistors when they are providing variable fan speed.
Circuitry I have seen with resistors controlling the switching rate of the transistors doesn't usually require them to be cooled as they don't pass as much current.
Matt.
I haven't seen a wiring diagram for the blower motor assembly so I am not 100% sure how it is setup however commonly the resistor pack is used to provide variable fan speed and a transistor module is used in place of a relay to provide full power.
It might well be different on the Lexus with the resistor pack working with the transistor module, I couldn't say. As they are two separate modules I would assume that they aren't directly related, however you know what they saw about assumption :-)
The working diagram I saw had the resistor pack located in the airstream of the fan assembly which is usually done to cool the resistors when they are providing variable fan speed.
Circuitry I have seen with resistors controlling the switching rate of the transistors doesn't usually require them to be cooled as they don't pass as much current.
Matt.
01-17-08, 07:47 PM
#37
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Installation Success. It is not that difficult, its just in hard to access place. The transistor is in the far right corner of the passenger side. It is mounted upside down and the screws are hard to get to. I had to use a rachet screw driver since no screw driver would be small enough height wise to fit. The climate control now switches speed and everything works great.
01-18-08, 04:08 AM
#39
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Installation Success. It is not that difficult, its just in hard to access place. The transistor is in the far right corner of the passenger side. It is mounted upside down and the screws are hard to get to. I had to use a rachet screw driver since no screw driver would be small enough height wise to fit. The climate control now switches speed and everything works great.
So how long did the whole job take? The transistor is all you had to replace?
Pics would definately be great if you have them.
Thanks for the info!
01-19-08, 10:36 AM
#40
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I just did the job last night, took me about 45 minutes from start to finish.
After removing the glovebox it's not obvious where the transistor module is however the resistor module is easily visible. It's pretty much in the centre of the assembly looking at you.
If you follow the wiring down from the resistor module it takes you to the transistor module.
It is impossible to get a screwdriver in there without removing the carpet and the plastic cover panel over the engine ECU. Once those are removed I could get a stubby screwdriver in without any problems.
The clips on the wiring are difficult to unlatch, I had to pull away the foam so I could find where they were latched.
Impossible to get any pics, you just can't get in there to see anything.
Refit wasn't hard, with the ECU cover removed you need to be careful that you don't drop the screws and lose them forever.....
Matt.
After removing the glovebox it's not obvious where the transistor module is however the resistor module is easily visible. It's pretty much in the centre of the assembly looking at you.
If you follow the wiring down from the resistor module it takes you to the transistor module.
It is impossible to get a screwdriver in there without removing the carpet and the plastic cover panel over the engine ECU. Once those are removed I could get a stubby screwdriver in without any problems.
The clips on the wiring are difficult to unlatch, I had to pull away the foam so I could find where they were latched.
Impossible to get any pics, you just can't get in there to see anything.
Refit wasn't hard, with the ECU cover removed you need to be careful that you don't drop the screws and lose them forever.....
Matt.
01-19-08, 11:32 PM
#41
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excellent. Its amazing how the dealer can quote 2hrs for that job. It kind of makes you laugh when you see how small the part is. I cant believe that thing cost me $160. Looks like something your local radio shack would have.
05-11-09, 11:30 AM
#42
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ok, Back from the Dead AGAIN....
I see there are only 2 possible parts... Did anyone have the problem come and go? Sometimes it would work? If so which one was it... the resistor and the transistor?
Thanks Guys!
I see there are only 2 possible parts... Did anyone have the problem come and go? Sometimes it would work? If so which one was it... the resistor and the transistor?
Thanks Guys!
08-24-09, 10:13 PM
#43
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Excellent, this has been an issue on my sc for 6 years :P
I have had a bit of experience replacing the blower motor resistors on a number of cars. so naturally I checked the repair manual to find the blower motor resistor location. However, when i took everything apart, I was stunned to find that there was not resistor in the location where its supposed to be. I could see the spot where its supposed/used to be (maybe on older models only). So I suspected the transistor, but didnt know for sure and i couldnt find anyone on clublexus or LOC that knew for sure. When i took it to lexus, the idiot "senior tech" said he couldnt duplicate the problem!!! It does this all the time all of the time, maybe 2 or 3 times in 6 years the blower motor would drop down to selected speed briefly, than go back to full speed. I didn't want that jackass even working on my car anymore, there were other issues with him as a tech as well, so ive done pretty much everything myself from that point on. Now i just have to find the part!
I have had a bit of experience replacing the blower motor resistors on a number of cars. so naturally I checked the repair manual to find the blower motor resistor location. However, when i took everything apart, I was stunned to find that there was not resistor in the location where its supposed to be. I could see the spot where its supposed/used to be (maybe on older models only). So I suspected the transistor, but didnt know for sure and i couldnt find anyone on clublexus or LOC that knew for sure. When i took it to lexus, the idiot "senior tech" said he couldnt duplicate the problem!!! It does this all the time all of the time, maybe 2 or 3 times in 6 years the blower motor would drop down to selected speed briefly, than go back to full speed. I didn't want that jackass even working on my car anymore, there were other issues with him as a tech as well, so ive done pretty much everything myself from that point on. Now i just have to find the part!
