No power to AC compressor (1 Viewer)

[Seth_O]

Now that the hot weather is returning I need to get the AC working in my '86 FJ60.

When I turn on the AC the blue button lights up, but I am not getting power to my compressor, and I cant figure out why. I have confirmed I have power to my amplifier, and my pressure switch is passing power just fine. If I jump 12v to the compressor it fires up just like it should. I cant read the EWD well enough to get any further than that. I know there is a VSV in the mix, that appears to adjust the RPM's based on the additional load from the AC, I don't think it affects power to the compressor clutch.

Anyone have any ideas on where I can check next?

 

[FJ Silver]

Probably not enough pressure in the system... I'd hook up some gauges.
The clutch won't engage if the pressure is too low.

 

[Seth_O]

I checked to ensure my pressure switch was passing current, I had 13v going into the amplifier from the switch line.

 

[fjc-man]

Just a thought, is a rpm signal needed at the A/C amp to get power to the A/C clutch? If so, see if it’s getting there.

 

[Seth_O]

The EWD indicates 2 circuits inside the amplifier, one for low RPM's (under 950) and another for higher RPM's. But I dont understand how they work, so not sure what I would check for. Tach signal I assume, but I dont know how to test for that?

 

[fjc-man]

Tach / dwell meter?

 

[BadReligion]

Even though you have 13v at the pressure switch, I'd still hook up a manifold gauge set and see what pressures you get.

 

[Seth_O]

Its definitely something in my amp circuit. When I jumper the yellow 12v wire to the b/w wire thr compressor fires up and runs just fine with the switch pressed.

 

[MoaByte]

I think it runs without the VSV so long as you cut that resistor (or whatever it is) on the AC amp because I don't need the idle up.

 

[Seth_O]

I found this pic:

And ran the tests. Everything passed EXCEPT - my continuity from 9 to ground, and the A-6 battery power at start. Although, when I check the wiring diagram 8 & 9 are both used only for vehicles WITHOUT a heater, which I have, so not sure that matters either.

 

[Seth_O]

Found that connector bay #7 goes to the tach and hooked up an analog meter to it and got nothing. I then checked continuity b/n that connector and the connector on my tach and got nothing. Not sure if that means anything though?

 

[Seth_O]

Hah! I had a success! Connector #9 is supposed to pass constant continuity with ground, but for me for some reason it was not. So I jumped the back of 9 to the back of 6 (constant ground) and everything worked as it should.

Now I just need to trace 9 down to where it is loosing continuity.

 

[Seth_O]

For future posterity: connector 9 on the plug goes to the thermistor, so if the thermistor is bad, it wont provide a ground path on that circuit, preventing the compressor from turning on.

Apparently you can test the thermistor by testing impedance on the connector going into it. There should be something like 3500 ohms at 40* F ambient temperature (resistance increasing as it gets colder.)

In my case (~72*F) I was getting ~6500 ohms of resistance, i.e. a bad thermistor.

 

[fjc-man]

A damn evaporator temperature sensor.

 

[Hammer45]

Awesome Seth. You is a smart dude! Glad you’re gonna be cool this summer.

 

[BluewaltFJ60]

I found this pic:

View attachment 2675753

And ran the tests. Everything passed EXCEPT - my continuity from 9 to ground, and the A-6 battery power at start. Although, when I check the wiring diagram 8 & 9 are both used only for vehicles WITHOUT a heater, which I have, so not sure that matters either.

I have looked through all my FSMs and can't find this diagnostic diagram. Where is this Amp diagnostic located?
Just picked up my FJ60 from my mechanic, did the conversion to 134a, can't get the system to work, he can hotwire it and compressor runs and blows cold. He thinks the Amp may be bad but after reading all the various threads on AC I am thinking it might be an RPM issue. Full disclosure, I am running fully de-smogged, Weber carb, and HEI Distributor. Have a feeling the original ignition coil circuit is need for an Amp that to sense the RPMs, I guess clipping the diode off the Amp board is the trick.....or somehow doing some inventive wiring?

 

[BluewaltFJ60]

did a part number search, is this legit?

https://trupar.com/p/toyota-forklift-amplifier-88650-60020

 

[Seth_O]

I have looked through all my FSMs and can't find this diagnostic diagram. Where is this Amp diagnostic located?
Just picked up my FJ60 from my mechanic, did the conversion to 134a, can't get the system to work, he can hotwire it and compressor runs and blows cold. He thinks the Amp may be bad but after reading all the various threads on AC I am thinking it might be an RPM issue. Full disclosure, I am running fully de-smogged, Weber carb, and HEI Distributor. Have a feeling the original ignition coil circuit is need for an Amp that to sense the RPMs, I guess clipping the diode off the Amp board is the trick.....or somehow doing some inventive wiring?

I dont remember where that diagnostic table came from unfortunately. I found it somewhere on the interwebs.

 

[BluewaltFJ60]

so I am still puzzling on this issue BUT before I remove the diode from the Amplifier to bypass the RPM control (fix found on another AC thread) I called my local mechanic (who just did the conversion and recharge on the AC system), I ran this by him, how about you take the Tach lead from the (HEI) distributor, splice it, and run the 2nd lead to the AC amplifier circuit? He seemed to think that would work, and he spent some time looking over all the schematics when he was working on the truck.