luvLexus95

I'm a recent owner of a 95 ES300. My blower stopped working and have been wracking my brain trying to figure out what the cause is. Here are the issues;

1. The fan only blows at low speed. The display shows that the fan speed is increasing, but nothing happens.
2. Error code 21. I ran the HVAC diagnostic and only that code came up. No other previous issues and no other codes appear.

I went to a wrecker and swapped out the A/C Power Transmission (the part that slides into the back of the system, immediately to the right of the gas pedal) and that did nothing (unless that one is fried too).
From what I have read here, code 21 is a light sensor and given that it's mid-November, shouldn't impact the hvac system nor does it require any parts or service.

If I am wrong, please let me know and if you have any tips or pointers, please let me know...I would really appreciate it.
Thanks,
Rich

LeX2K

There are two components involved in the fan speed besides the HVAC controller check it out. 88750A and 87138
https://www.japan-parts.eu/lexus/us/...&pa=8875033010

How did you retrieve that error code?

luvLexus95

Thanks for getting back to me. Great looking cars!!
The part 88750A looks like the part I swapped out from the wreckers. This fits in near the firewall to the right of the gas pedal.
87138 looks like the resistor. I am currently trying to find where that is located to see is that's the issue. Do you know where this is located?

I retrieved the error code by pressing the "Auto" and "air recirculate" buttons simultaneously and turned the ignition key "On". My understanding is that any previous issues would appear in the display without hearing a tone. Existing issues appear with a tone you can audibly hear.

Thanks again!!

luvLexus95

I forgot to mention that I had discounted part #87138 because I thought if the resistor was faulty then I would only have the option to turn the fan on high speed (either an all or nothing) but not the opposite.
Thanks

LeX2K

I don't know where the resistor is, maybe near the blower motor? They are usually in the path of airflow to cool them off but this could be different since the resistor is used in conjunction with that transistor circuit. Which means the resistor might be causing your issue.

Also the used part you got could be cooked. A schematic would be helpful don't think I have one for your car.

edit- here's the wiring diagram for a 1993 hopefully it's close enough page 199 describes how the blower motor works.
edit 2 - page 30 shows the location of the resistor it is described as "low speed resistor".

luvLexus95

I pulled the glove box, thinking the same as you, kept in the path of the airflow to stay cool. It looks like there is one above the blower, on the righthand side beside the dust filter. Definitely not it according to the diagram you've attached. I was thinking the same about the part and have no clue how to bench test it. I will have a look and let you know about the resistor.

Arsenii

Hello,

From the wiring diagram, it seems like there are three controls for the blower motor speed in that car - Blower Resistor, Power Transistor and Extra–Hi Relay. Blower Resistor serves to provide a low speed, once the climate control is at the lowest setting, there is no control power coming to the Transistor, so it is closed, hence the blower spins slowly. Once the A/C Unit gives a signal to a Transistor, it opens up and allows more current to go, bypassing the resistor. The speed in the "middle" position is controlled by the voltage in the signal wire for Transistor (at least that is my understanding). And lastly, for the full blast, the A/C Unit activates a so-called Extra–Hi Relay, which connects the motor directly to Ground.

Does your blower motor work on the max speed? Since it has a different circuit for the high speed, it should work on the highest setting. If the blower motor works at the Low speed, then it is not a Resistor. If it works on both minimum and maximum speeds, then it is probably a Transistor that is bad. I would also suggest to inspect the wiring, since sometimes it starts crumpling because of overheat.

And lastly, it may be that your blower motor itself is not good. Power Transistor has a built-in temperature fuse, which shuts the control off in case of an overheat. If your motor is hard to turn or something like that, it may trigger protection, hence why it doesn't work. Both the resistor and transistor are rare to go out, and if they do, there is usually a reason for that.. Both the resistor and transistor are marked on the schematic linked above as 88750A 87138 respectively.

P.S. Completely forgot about a Code 21 you have - it is nothing to worry about, it will pop-up each time you are trying to run diagnostics in the dark environment. Just try running the diagnostics again, but this time under direct sunlight.

Hope this helps and best of luck!

LeX2K

That's how I read the schematic as well, although it is a bit convoluted. If you want to really confuse yourself read the description of how the blower speeds work.

If you can't find a good used one check this site they are generally cheaper than a local or online dealer even with shipping
https://www.amayama.com/en

Arsenii

Well, that is part of the reason why it took me so long to respond actually, it is quite a bit confusing..
Though that said, it seems like it starts to make sense after you stare at it for a while. As I wrote earlier, you have a resistor for the lowest speed, then the transistor kicks in, which is controlled by the amount of current supplied by the BLW pin of the A/C Unit, the maximum speed is done by the use of a relay, which, in essence, connects the motor directly to the battery. As for the VM terminal, I am not exactly sure about what exactly it is, but my guess would be that it is a pin to monitor the voltage supplied to from the collector pin of the transistor to "control blower air volume precisely" (that is how Toyota puts it), it is probably there to make the control more precise, and for an Auto mode, since in that mode, "the a/c control assembly controls the blower motor steplessly."

At least that is how I understand it.. Unfortunately, there is not a whole lot of information about it, since Toyota bailed on that idea by the end of 1990s, and started using a Linear Controller, which is probably for the better, since it is more durable, and gives you seemingly endless possibilities.. Hope I didn't confuse you even farther with that though..

Hope this helps and best of luck!

luvLexus95

LOL...not at all. I fell in the mud right about here..."by the BLW pin of the A/C". It's all good though. I am starting to make sense of it.

To answer your question, the fan only blows at the lowest speed. Whether I have the climate control on by pushing the "Auto" button "On" or I am pushing the fan speed button up with my finger it only blows at low speed. Logically it tells me it's not a resistor because a resistor resists the flow, which it is not.

Part #88750A (Power transistor): I pulled one out of a wrecker, connected it to the plug from the existing one (while the transistor was still installed) and the fan speed options didn't change...only low speed.
When I pulled the glove box out, I noticed one of the three screws holding the blower in place missing as well as two screws that attach a harness of bundled wires missing as well.

Onward ho!! Thanks to both you and Lexus2000 for all your help and advice!!

Arsenii

Huh, a good sign in a bad way.. Someone was there before, which may indicate all kinds of bad things, considering the fact that they forgot the screws. That makes me wonder if the A/C Unit sends all the necessary signals..? All that may also indicate a damaged wiring as well, so be on a lookout for any torn, damaged, fried, etc. wires, and if you see one, use wires from the junkyard to repair the damage.

Try putting a light bulb instead of the blower motor to eliminate the possibility of a motor failure. You can also try reaching for the Extra-Hi Relay, which *it seems like* is marked as 88630M on the diagram and see if it gets both the power and the signal. Pretty much everything in the car is controlled by Ground, it will be pain to diagnose with just a regular multimeter, so I will suggest you to get or make a test light (basically a light bulb with a couple of wires). You can see which set of pins is for the coil and which is for the switch by measuring the resistance between relay pins, the ones that have resistance between them are for the coil, other two are for the switch. That relay breaks the Ground supply for the blower motor, so connect one lead of the test light to any 12V supply, and the other to one of the switch pins on the relay, the test light should light up on one of the pins, indicating Ground supply; test the other switch pin by measuring continuity between it and one of the blower motor pins. As for the coil, it should have a constant 12V supply to it, and is controlled by the Ground supplied by A/C Unit, meaning that if you were to complete the circuit by adding a separate Ground for the coil (in other words, bypass the A/C Unit), it will trigger the relay, and the blower should set off at full blast. Set the blower speed and temperature to maximum, then check the power supply and see if the A/C Unit supplies Ground for the coil; if not, it may indicate a fried A/C Unit.

All that should at least give you both Minimum and Maximum speeds, but as for the middle, emmm... I am not exactly sure a 100%, but I have a theory - the A/C Unit's BLW pin supplies voltage to the pin 2 of the Power Transistor, therefore opening it, and by varying voltage on BLW pin (consequently Pin 2 of the Power Transistor), it varies the voltage supplied to the blower motor, thereby controlling its speed. You can measure if you at least have something coming to that pin in the first place, since otherwise the transistor won't open, and you won't go past the first or max speed. I would probably suggest using a multimeter there, since the voltage should not be that big.

Again, that is my theory on how that system works, I am not sure if that is right or not though, so please be careful not to make it even worse. That is pretty much all I can think off at the moment..

Hope this helps and best of luck!

luvLexus95

Yesterday I received part #88750A, the power transistor that is immediately to the right of the gas pedal. I pulled the plug from the existing and connected it to the new one (leaving it lie on the floor beside the gas pedal). I turned the ignition on and still only had low fan speed even though I was adjusting the fan speeds using the up and down arrows on the control panel.

I thought I would try a test to see what would happen if I disconnected the heater bower resistor (part #87138). No change, still low speed.
Then I disconnected both. The result was no fan. This leads me to believe that the resistor has blown.

If so, how do I remove it? From it's location above the gas pedal, I can access one screw but the second screw is right against the firewall and can barely see it behind a covered wire going up into the dash and with the gas and brake pedals am having a challenge trying to see, access, and remove the screws.

Any suggestions would be appreciated.
Thanks in advance,
Richard

Arsenii

Huh, that is really interesting..

Did you check the Extra–Hi Relay? You should have the highest speed even without both transistor and resistor connected, you just need to make sure that both Power and Ground are coming to it where they should, just like I described in my previous post. It is important, since it may indicate either bad wiring or a fried A/C Unit.

You don't necessarily need to remove the Resistor to test it, you just need to measure the resistance between its leads, which should be around 1.8 – 2.2 ohms. What is more concerning is that you have power coming to the transistor at the lowest speed, which (at least from my understanding) you should not. From the wiring diagram, the resistor is always connected to the blower motor, so if the Blower Relay is active and only Resistor connected, you should have the lowest speed. Check of the blower motor will work with the Transistor disconnected, if not, check the wiring that goes to the resistor.

Hope this helps and best of luck!

luvLexus95

I'm trying to find the extra high speed resistor. It seems the 94 diagram in this tread (LEXUS ES300MCV10L-BTPGKA - ELECTRICAL - HEATING AIR CONDITIONING HEATER UNIT BLOWER | Japan Parts EU (japan-parts.eu) and and my '95 have some slight differences as I can only find the low speed blower resistor and the power transformer on the driver's side. I peeled the carpet and insulation back from the side of the console and didn't see or feel anything. Any suggestions?
Thanks

Arsenii

Well, I probably spoke too soon about that relay, after doing a bit more research I realized it will be ... a bit tough to reach to say the least.



It is still possible to check if the A/C unit even sends the Ground for the relay coil by checking a pin on A/C Unit marked below. I have attached an FSM for the Air Conditioning for a 1993 Lexus ES300, while it is not the right year, it is the best I could find. That said, at least from what I know, the pinout stayed the same.. That manual also contains information on how to check Power Transistor, Lo-Resistor and the motor itself, as well as labels for all the pins in the A/C Unit, so it should be quite helpful.



Hope this helps and best of luck!