[Rickl]

I do have a constant voltage from the ac amplifier, even when it is off. (it's around 13.3 dc). Couldn't make sense of the signal wire on ac or dc volts. It might be too small for my cheap meter to pick up but it does change (spike for a second) when the speed is adjusted.

Eric; You can download the repair manual for the AC system at the same location you found the electrical diagrams. The manuals contain a trouble shooting chart, and you seem very capable of following it.

One other simple test is to measure that the ground wire on the blower connector really does have a good connection to chassis ground.

The signal from the AC amplifier is a pulsating DC voltage, with a varying duty cycle. This can only really be observed with an oscilloscope, but an old analog voltmeter should at least let you see the voltage change as the duty cycle changes. A digital voltmeter is almost useless for this type of reading.

Do you see the speed ramping up on the LCD display when you try to adjust it?.

 

[Rickl]

Any chance it's the AC amplifier? I'd like to make sure it's the blower controller before buying a blower assembly.

Logical trouble shooting, I love it.

My theory is that the electronics inside the blower assembly act like a simple Triac controlled lamp dimmer, or speed controller. By varying the voltage on the gate (or more specifically the time that the gate is opened) we control the voltage getting to the device.

In this case it looks like the varying gate voltage is the SI signal from the amplifier, and the power for the motor comes on the B+ lead. Which may just stand for battery, or many older engineers still make reference to the B+ plate voltage used on vacuum tubes.

So you know that you have full battery voltage on the B+ line (Pin #3), and I assume you checked for a good ground on Pin #1, so you only need to see if the duty cycle of the 1v square wave on the SI line (pin #2) changes as you adjust the fan speed.

If you have a scope, then that's the way to go. Otherwise try using an old analog voltmeter ( with a mechanical meter and pointer) on the DC scale. Analog meters have the magic ability of displaying the "average" value of a varying DC voltage. When the duty cycle is near 1% on- 99% off, the meter will read near zero. at a 50-50 duty cycle the meter should read ~.5 volts, and at a 99-1 duty cycle it should read ~1v. Be aware though that depending on the meter, it may be difficult seeing a voltage this low.

Am going to jump connect the motor directly to connector E-53 and make sure we're good there. I did measure 13.3 vdc so no reason that shouldn't spin the blower motor too.

I assume you want to do this test to determine if the B+ pin on E-53 can deliver the proper current. As long as you're using jumper leads from the motor to the B+ lead, and not plugging E-53 onto the assembly it should be OK. I think if you were to short out the internal circuitry with E-53 connected then you could risk damaging the amplifier via the SI lead (Pin #2).

Or am I over analyzing, just buy a blower assembly from the junkyard?

You don't seem to be having any problem following the diagnostic procedures, so why not continue and make sure you are replacing the proper item.

EDIT: The location of the AC amplifier is shown on page AC-7 of the manual.

 

[Rickl]

I don't have a scope or analog meter. Ill try to borrow one. Or could I use a logic probe? I have one of those but never used it. There's always a first time.

The logic probe is designed to light when there is a logical "1" and be dark when there is a logical "0". In the world of logic, everything is based on 5 volts. A logical "0" is any voltage less than 2.5 volts, and a logical "1" is any voltage above 2.5 volts. Since the RAV4 amplifier is swinging from 0 to 1 volts, the logic probe will always show a "0".

Even if the voltage was a 0-5 volt signal, it is changing two full cycles per second. You could probably see that rate on a logic probe, but not if it was much faster.

It may be hard to locate an analog meter anymore. I have seen cheap ones sold at the automotive store, but they only had a 12v and 100v DC scale. I don't think you could see the voltage changing from the amplifier unless your meter had a 1v scale.

Since you have already pulled the blower assembly out, maybe you can find a friend who will let you plug it into his RAV4.

 

[Rickl]

I do have a constant voltage from the ac amplifier, even when it is off. (it's around 13.3 dc). Couldn't make sense of the signal wire on ac or dc volts. It might be too small for my cheap meter to pick up but it does change (spike for a second) when the speed is adjusted.

Dr. Dyno's statement about seeing the SI voltage change "but not knowing if the voltage was correct" caught my interest. When a device like the amplifier goes defective , the output voltage will remain fixed at 0V or it may stay at 1V or it may even go to the full supply voltage of 12V. The one thing it won't do is continue to fluctuate.

In your statement above, you said you saw a constant voltage of 13.3v from the amplifier. I assume this was on the B+ lead, but the spike you saw was on the SI lead.

Depending on the frequency of the pulses and the sample rate of the DVM the voltage can appear to be jumping all over the place giving you the impression you have a bad meter connection. So rather than seeing a rise/fall in voltage as you change fan speed, you just see erratic readings. The good news is that type of reading is not one of the common failure modes. So even though you cannot get a good meter reading, that in itself could be a roundabout indication of proper operation.

I was also thinking you might be able to use a low voltage (~1V) incandescent light bulb to monitor the SI voltage. You should see the brightness change with the varying speed settings. A LED will not work because 1V is not sufficient to operate aq LED, and LED's are not really dimmable devices.

 

[Rickl]

There are some components inside the blower that involves a couple capacitors, an inductor, a resistor and some kind of 5 leg bridge or regulator that is mounted to a heat sink. Took a picture of it and can attach if that would help.

Maybe it's time to post the picture.

There needs to be something other than passive components to perform this magic though. Is the 5 legged device the only non-passive "looking" component? It may be some type of regulator. If we can get the part number from it, and if we can find the spec sheet for it, we can do some more detailed trouble shooting.

 

[Rickl]

I will open it back up at my next opportunity, probably Thursday night. I like the way you were thinking about the erratic readings from the amplifier on the SI wire pointing to it not being the root cause.Eric

Well I wouldn't worry about taking it apart again if it's a lot of work because the chances are slim that any visible part numbers are anything more than a Toyota part number and not a standard electronic component number. I guess you can at least test the diode,inductor, and make sure the caps aren't shorted.

If you can't prove the SI voltage is pulsating, then it looks like replacing the blower assembly would be the easiest step, but since the amplifier circuit is much more complicated, it is more likely to have failed. Tough decision. The fact that you saw pulses on the SI signal is a little reassuring though.

You really need to determine if the SI voltage coming out of the amplifier is changing. Since you don't have a scope or analog meter (with a low volts scale), you could try a low voltage light bulb. If I think of anything else I will post a message.

Good luck, and please let us know what you find out.

 

[Rickl]

A friend has a Fluke 83V meter that looking in the operating manual can measure frequency and duty cycle. I'll get a chance to borrow it on Saturday.

I had a look at the Fluke manual and it sounds like this meter will be able to let you know if the AC amplifier is putting out the correct waveform. This certainly isn't your Father's multimeter. If you are interested you can download the manual here, and prepare yourself for Saturday.

Further looking in some of the exploded diagrams of the section AC-188 shows that AC Amplifier is accessible after removal of the dashboard brace and a couple air ducts. Anyone ever worked on this? Is it really buried in there that deep?

I just found those diagrams last night as well. It looks like 13 steps before you get to the AC Amplifier. Some of those steps involve removing the refrigerant, disconnecting the water lines, and removing the steering column and upper instrument panel. This is probably beyond my capabilities both mechanically and financially.

Hopefully the Fluke meter will tell you that you don't need to remove the amplifier.

 

[Rickl]

Eric, I'm glad that you found the problem, and thanks for letting us know what you found. It will probably help some others in the future.

You were lucky to find a scope. My company used to have all kinds of test equipment, but as things went digital and modular, we started to depend on built in diagnostics and card replacements. I don't think I could easily locate a scope any more.

Rick