TLTrance

I recently replaced the blower motor transistor (It had burned out -- I was not able to control the fan speed or A/C temperature -- it just kept blowing at a constant speed and temp) with a standard motor branded version, as opposed to OEM.

Has anyone done this before? I'm asking because I noticed that the lowest fan speed (1), is a bit "faster" (stronger) than the original lowest setting. Also, it seems that the heater doesn't really start kicking out heat until I turn the temp to the upper 70s, which is higher than before.

makk

The heater is unrelated to the blower transistor. It is possible it spins a bit faster, maybe the first setting has a lower resistance on first speed setting.

TLTrance

Yeah, it was just one of those things I noticed... now that I think about it, the heater "intensity" clearly has nothing to do with the transistor... However, if it is required for the correct operation of the A/C, then does this imply perhaps that the A/C part (cool air) is kicking in too strongly? Sort of like a "proof by negation"...

Not sure...

makk

Not really sure what you are getting at. The transistor has nothing to do with heat or cooling. It merely regulates the speed of the fan based on driver selected fan speed. On full speed, it bypasses the trans and blower spins max rpm. Next fastest speed and the ground circuit goes through a small resistor. So on and so on.

TLTrance

Makk: When the transistor is blown, I believe the car also disallows the use of A/C, even though the device itself isn't actually responsible for the A/C functions.

makk

The a/c is a separate system and not related to blower function.

TLTrance

You keep saying this, but first hand experience tells me that at the very least the A/C function is disabled when the transistor is blown. Anyone else on this forum would like to chime in?

The blower transistor may not regulate A/C function explicitly, but when it is blown, there must be some other "logic" in place that the car itself is responsible for that prevents cold air from coming out. So, semantics aside, when the blower transistor is blown, the A/C does not work like it is supposed to.

Jackass

If the transistor is blown, the blower doesn't work which means you have no heat and no A/C. No fan == no cabin temperature controls besides the windows.

makk

Not always true. It commonly fails and you have high speed blower operation only. Your heater and air conditioning work as usual.

nfnsquared

^^^Yeah, if the transistor malfunctions and assuming transistor Collector-Emitter continuity is maintained, the blower motor will just receive a straight ground and run at high speed only.

If the transistor totally burns up and Collector-Emitter continuity is broken, then the blower motor will not run at all.

There is a Blower Feedback signal/current that is returned from the Collector side of the transistor to the Climate Control Unit. I assume that if there is no signal/current sent to the Blower Feedback circuit (e.g. the transistor is complete toast and no signal/current is sent either to the blower motor or the Blower Feedback circuit), the Climate Control logic will shut off the rest of the HVAC functions.

I don't know, but the Blower Feedback logic may even be smart enough to monitor current output from the Collector to tell if the transistor is sending the correct current to the blower motor for the selected fan speed.

Again, exactly how the Blower Feedback logic functions is an assumption on my part, but it would make sense to shut down the rest of the HVAC system if the blower motor is not running and to also monitor the current sent to the blower motor by the transistor (which then could theoretically detect a failing/malfunctioning transistor and set the DTC "S" indicator signal or the DTC 1241 "A problem in the blower motor circuit". [Service Manual page 21-44] )

I have the ETM but don't have time to scan the diagram right now (pp. 60-1 and 60-12). I'll try to get it in later tonight.

Jackass

For the most part, we are all saying the same thing. If the transistor is shot, you do not get the expected outcome from the A/C and/or heater system. The systems in general are fine, but the blower that moves the air inside the cabin is not functioning in the expected manner.

nfnsquared

As promised:

fulla

Hey guys, I'm new here, my blower does not blow at all, high, low or in between. I can adjust the temp up/down and cut the AC on or off, but nothing happens except the digital display going up/down (temp) or the AC saying on or off, any ideas what's wrong? Thanks for any help.

fulla

Come on guys, any help at all? Can anyone tell me the fuse numbers to check? I looked at the fuse covers ( inside the footwell and under the hood). Looked like one under the hood had "blower" marked on the cover, it was a 40 volt I believe but it was good. I need help with the location of the fuses or relays. I took the cover off of the bottom of the glove box to access the wires and look around, everything looked good to me. How bad do the wires look if they are burnt, like some people are saying might be a common problem? Any help would be appreciated, thanks in advance!

Vlad_Type_S

iTrader: (3)

Welcome to the site!

Are you driving an 04-06 or 07-08? I believe they have (albeit small) differences in the fuse boxes. I have the shop manual for the 07-08 so I might be able to help you locate those. Also, fuses are rated in Amps, not Volts.

A google search will provide you with methodical troubleshooting methods for a blower motor: most cars have a very very similar HVAC system architecture. Here are the possibilities I can think of off the top of my head (in decreasing order of likelihood):

1) Bad Blower Motor Relay
2) Blown Fuse
3) Bad Resistor Card
4) Burnt Out Blower Motor
5) General Electrical Problem (i.e. damaged wiring/contacts/loose connection)
6) Defective Control Unit

To troubleshoot this yourself, you'll need a DMM. (Digital Multi-Meter) You can pick one up for probably less than 20 bucks.

fulla

Thanks Vlad, I have an 04 TL. I bought a new resistor/transistor but did not install it yet. Reading some post and the Internet it seems like a lot of people say that if the rest/trans. Was bad the fan would still run on high speed, mine does not run at all. I'm going th try and run 12 volts directly to the motor and see if the motor spins, that would eliminate that, can you tell me the number(s) of the fuses and the locations? I know you said you have an 08, but I'll compare it to mine to see if they are the same, also, where is the relay? Do you know how to check the resistor or relay with a volt meter, if so, I have one of those already . I did check the wires going directly into the blower, and it said 14 volts I believe (don't remember exactly its late here) ill double check in the am. The funny thing is it was ready that with the fan set to off and the fan speed set to high! Hopefully it not the control unit, that sounds expensive. Thanks again for your help, it's getting ready to be summer and I need the AC. I like to try and fix stuff myself so I know it's done right, I've been burnt by shop before.

johnny3

You have to remove the glove box to get to the resistor I'm pretty sure I've seen it when I changed my AC duct work filter, just change it out & all will probably be normal again, also will be a good time to change that filter. Do a search on ac filter or resistor & you should find lots of info.

nfnsquared

No you don't (at least for an 04TL), it's easily accessible under the passenger side dash right above the carpet line, no need to remove the glove box.

Read my post #10. If the transistor is totally fried, the motor won't run at all. It's a 5-minute DIY replacement. My bet is the new transistor will fix it.

fulla

Thanks nfnsquared all all that helped, I have a new resistor and will replace it in a few min. Will let you all know if that fixed the problem, I certainly hope so!

fulla

Thanks again for everyone's help, I just replaced it, kind of reluctantly, because of it being a $55.00 electrical part that I can't return, but....... It works!!!!! Now I'll be cool in the hot VA summer months. Thanks again everyone.

nfnsquared