Gevo

Hello, solving yet another problem here, this time with the AC circuit.

It is insane to me how they managed to make it such a cumbersome circuit. Alas, this is the symptom.

When AC switch is turned on the green light on the switch comes on, and with the FAN circuit turned on the AC compressor is NOT engaged. The AC condensor fan is also NOT engaged.

I went to get her re-charged with refrigerant, and the mechanic checked it out for me and concluded my Amplifier is NOT functioning properly. He jumped the the output wire with a 12 volt feed (output to compressor clutch, which of course i checked earlier and its working) boom, nice cold air and both AC fan and clutch working. So, I thought ok great, new amplifier... However being an Engineer I decided to look at the circuit myself and make sure I'm not wasting money and not solving the problem. I checked the Amplifier circuit as per the FSM, and it failed in two places. NOW, after thinking long and hard, I think there may be misinformation on the FSM. Here is the page for diagnosing the AC amplifier circuit. (My vehicle is 1991, this FSM is 1993 to 1995 i believe, perhaps issue lays there??, hasn't failed me yet though)
http://personal.utulsa.edu/~nathan-b...ng/22airco.pdf

At the bottom it says to cross 2 with 5, those are the Yellow-Green and Yellow Green on the wiring diagram which can be seen here as connector # 2 & 5 of the Amplifier:
http://personal.utulsa.edu/~nathan-b.../2aircondi.pdf

and here, as per the diagram, the Mechanic used:
https://lh4.googleusercontent.com/_2...p=w707-h822-no

The problem is, it says when the system is on MIN COOL (which means moving the mechanical lever to all RED side???) (or Blower fan onLOW??? I tried both) that the resistance is supposed to be 3K Ohm. Well, it wasn't, it was 0 ohms for both conditions. I looked back at the diagram and You can see that connector 2 (Yellow Green) is directly connected to connector 5 (also Yellow Green). What gives? How is the resistance supposed to change? If so, then which component is at fault on the circuit?

I'm not convinced that the amplifier is broken, if the amplifier isn't getting all of the right readings from the sensors on the circuit it is supposed to NOT turn the AC fan and comp. clutch on.

If anyone has a great idea, please post.

My next steps are to mimick the supposed signals that the amplifier is supposed to see and see if it then turns the ac on or not.

Regardless though, is there an error in the FSM here??? Or I am missing something.. which of course is more likely..

oldblue

don't over engineer it. if it tested bad, replace it. sometimes over thinking something will just make your brain smoke.

scope103

Boy, that's a head scratcher.

First, the diagnostics on AC-31 are not to test the amplifier, but the sensor side (the "amplifier circuit") that feeds the amplifier. The amplifier is unplugged during the tests, and you're probing the harness side. I think you've got that.

Second, I agree that measuring between pins 2-5 of the harness should be a dead short per the schematic. So either the diagnostic is wrong or the schematic is.

Third, what should be the difference between "max cool" and "min cool"? At first I assumed (as I think you did) that it referred to the putting the temperature control all the way to blue or red. But that control is strictly mechanical (it works the mixing valve), and doesn't change a resistance anywhere. What DOES change a resistance is the blower speed control, so maybe that's what they're referring to? But no, the schematic shows that the resistors switched by the speed control don't connect anywhere to the amplifier. Sigh ....

I've confirmed the 2-5 short with other schematics I have; I'm pretty sure the diagnostic is wrong. And senseless; I can't think of any control that would change resistance between "max cool" and "min cool."

So I'm no help.

RJR

I think that the "min cool" vs "max cool" has to do with the two different speeds for the AC condenser fan up by the radiator. Min cool comes on whenever the compressor is running. A pressure switch turns on max cool and speeds up the fan if the coolant pressure gets above some predetermined value.

Gevo

Scope, that's pretty much exactly where I'm at as well.

RJR, you may be right about the AC fan circuit, but that wouldn't come into play when checking the harness side (or sensor side as scope said) for pins 2 and 5.

So, it's a million degrees outside, I will go tomorrow get her refilled (since new hose) so I can test the pressure switch as well. Since there is low pressure it is currently doing it's job and disabling the circuit. I forgot to mention this part earlier, but fear not, the system was just charged when the mechanic and I were searching for the cause of the issue. So, when charged the AC fan and the Mag. clutch were NOT engaged when they should have been.

I'm confident I'll be able to pinpoint the problem tomorrow.

But that won't solve the FSM's schematics vs. testing procedures issue

Gevo

RJR,

I think you are right about the min/max cool being related to the condenser fan. In this (non FSM) circuit diagram it shows two relays in the fan circuit in series with a resistor. I assume one relay on is min cool, two relays is max...

Ohh, Toyota ENgineers... !

Gevo

Well I got the refrigerent filled today and tested the circuit. The AC cut off rely was the culprit, I removed it cleaned it tapped on it while giving it 12 volts. And it started working. Plugged everything in and its good to go! It turns out my suspicions that it is NOT the amplifier that isnt working were true. The mechanic was wrong.

Now I have AC, hopefully no more leaks