A/C Light Still blinking after full system EVAC and refill.

So my truck has the blinking light issue and I have been working on it for a little and am at a point where I need some help from someone who has some experience and knowledge about these trucks.

I have tested most of the common issues on the AC system these trucks have and have gotten to the point where I evacuated all the refrigerant pulled it into a vacuum of 30 PSI. I held it there for an hour with no drop in vacuum. I then recharged to 1.30 Lbs. of refrigerant as is listed under the hood. The light still blinks right when I turn the truck on. The high and low sides equalize after turning the truck off at about 100PSI. Once the truck is on and the light starts blinking if I switch between defrost and dash vents the light will light solidly for a few seconds and my pressures start approaching normal range after about the 5th time cycling it my low side gets to about 35psi and my high hits about 275 then the AC will run without issue until I turn the truck off. It's like something is kicking off the compressor when I first turn on the truck not letting the pressures build to operating pressures. Once I cycle the defroster and it slowly builds to operating pressures it runs fine is ice cold and have zero issues.

I have checked the mag clutch and compressor, and everything is working fine. I replaced the AC amplifier I have verified the mag clutch relay is good, ang the compressor grounds seem solid and the compressor are fairly new. I'm at a standstill on what to look at next. Thanks for any possible help.

 

The flashing A/C light is when the A/C amplifier does not detect a speed signal from the compressor lock sensor after commanding the MG CLT relay on.
Possible causes are:
Open or shorted wire(s) in the lock sensor circuit
Bad lock sensor
Internal problem in the compressor
Open or shorted wire(s) to the MG CLT relay
Open in the wire from the MG CLT relay to the compressor
Failed compressor clutch
Belt slipping
Failed MG CLT Relay
Failed A/C amplifier

You can check the Lock Sensor circuit at Pin 10 (Red/White) Connector IH1 behind the glovebox (3rd wire down on the left of the connector shown)
Meter connected between a known good ground and the Red/White wire when the A/C is turned on you should see it briefly go to 12v and then drop to about 2.59v and stay there while the A/C is on. This can't be used to tell if the sensor is generating a signal or not but it will tell you whether or not the circuit is intact or shorted to ground.

 

Very helpful I'll look into that. I was going off of a post I found here to troubleshoot and it didn't mention that at all. The post I used was this one. https://www.tacomaworld.com/threads/a-c-light-blinking-troubleshooting-guide.440200/ Looks like I have another rabbit hole to start down.

Also, my thought process was also that the lock sensor itself must be good if once the pressures are up it will either work or it won't the lock sensor doesn't seem like something that can go in and out I would assume it's either functional or not.

 

"Internal problem in the compressor"

That's what caused my blinking A/C light. I needed to get a new compressor.

 

I guess that will be my last ditch effort. Like I said newer compressor so hopefully it isn't that.

 

I mean that was just an observation I made when testing the circuit with a meter on a known good (my truck), an oscilloscope is really the only way to see if it's generating a signal or not.
It's a Hall Effect type sensor but it generates a very subtle signal (only about 0.5v peak to peak) that looks more like a VRS type sensor signal.

 

Is there a way to test it or should I just swap it to see if it fixes it. I'll be at about $250 I've spent towards fixing it so about what it would of cost to get it diagnosed in the first place.

 

The only other test I have and it's about as experimental as putting a meter on the lock sensor circuit is a 150 mA test light from ground to the lock sensor circuit, on my truck it blinks dimly with the A/C on.
Beyond that an oscilloscope is the only testing option besides checking wiring integrity with a meter.

 

So I tested it the way you said to in your response above with the AC off and I test it it goes to about 3.5v and holds so my circuit is good.

 

Same for me.

 

Hate to ask but I've read a few times, in other threads, the flashing light and no A/C was found to be a ground wire for compressor that is under a screw with no lock washer, was found to be the cause. I'm not as young as I was, but would like to find and check this ground wire before taking to a shop. Is this ground wire connection somewhere that I can see if I get under the front of the Taco? or is it like so much other stuff, can't see it till I take off 10 other parts?... Any help appreciated.