Blinking AC light....may have solved mine

About 2 months ago my power steering got notchy. I figured the truck has 130,000 miles on it, PS pumps fail, so I replaced it. I also replaced the serpentine belt. All was fine after that.
About 2 weeks ago my AC light started to blink (it would stay on for a few seconds and then blink). I had someone turn on the AC while I watched the compressor....and it ran for a few seconds and then disengaged. I replaced the rotation sensor on the compressor, no change.
I didnt have time to dive into it further. Two days ago it rained, wind-driven sheet-rain. Went to drive the truck and the steering was again notchy.
Then things began to make sense. The old power steering pump had probably not failed. Neither had the AC system. They have one thing in common: the drive belt. Power steering was fine at first because it had a new belt, and if the belt even slips a little the computer will disengage the compressor.
Being an old guy, I sometimes overlook the subtleties of newer tech, like serpentine belt tensioners. I didnt even think that it could be the problem. I have a new one on order and Ill update you all when I replace it.
I bought a PS pump that I probably didnt need and a sensor I didnt need. And Im pretty sure it will all be solved with a new tensioner.

 

UPDATE:
Got the tensioner and installed it today. No difference. PS pump still notchy but the new tensioner revealed a very noisy upper idler, between the PS pump, the water pump, and the AC compressor. Ive ordered a new upper idler (didnt order the lower yet, want to see what happens with just the upper).
It drives me absolutely crazy to throw parts at a problem.....but this one is a gremlin and Im determined to solve it!

 

The blinking light means the compressor RPM, and Crank RPM do not match.
You say you have replaced the compressor pickup sensor with no change.

I'd want to see if you have a bad power steering pump with a "sticky" spot in it.
When the pump stick, the crank will out run the belt, and the A/C clutch will be held back by the power steering pump.

Or....You just might have a bad compressor.

 

The power steering pump is 2 months old. The AC compressor runs (shuts off after a few seconds). The PS pump problem and the AC problem popped up almost simultaneously. After changing the tensioner the idler made a lot of noise until the truck warmed up. I listened to the bearing with my mechanic's stethoscope and it was really grumbling. Needs replacing regardless.

 

Sounds like the compressor is seized. The mag clutch engages and once the compressor speed sensor doesn't sense rpm it shuts it down. Keep doing this and you'll burn up the clutch or at least shorten its life. You can manually engage the clutch with the belt off and see if you can rotate it by hand.

 

Compressor works fine. It actually runs for a few seconds and cuts off. Early in the investigation I removed the mag clutch relay and jumped the contacts and the compressor ran fine. I also jumped the AC pressure switch but that didnt help. It is wracking my brain, though.

 

Latest update:

Still have the same gremlin.
Heres a quick recap of what Ive done so far:
-Replaced PS pump 2 months aga
-A few weeks ago my AC switch light started blinking after a few seconds, so
-Tested AC relay and all related fuses
-With AC (mag clutch) relay removed I jumped the contacts and the compressor ran, seemed smooth enough.
-Replaced the AC compressor speed sensor, nothing.....

Then I gave up, had lots of other more important things to do, until my power steering got notchy again. So

-Replaced serpentine belt tensioner, when I started the truck heard a kind of grinding sound that went away after running for a minute or so.
-Checked pulleys with a mechanics stethoscope, upper idler pulley had a lot of bearing noise.
-Changed the upper idler and the serpentine belt (I had replaced it when I replaced the PS pump a few months ago) no change.
-Drove the truck and AC switch light stayed on when I was driving; as I pulled to a stop the light started blinking again.
-Sat in the driveway and brought the engine speed up to 2,500 RPM, then turned on the AC. Compressor stayed on until I reduced the speed to idle.....started blinking again.

So now Im thinking that the AC clutch is shot. On an older thread here someone had just replaced the outer clutch (without changing the pulley) and it solved his problem. Im going to do a thorough investigation of this and Ill update again.

 

That sounds more like the signal from the Lock Sensor is weak.

If the clutch was slipping it would be all the time.

Essentially it's down to the sensor wiring, the sensor, an air-gap issue, an issue internal to the compressor, or (very unlikely) the A/C Amplifier.

Only way to see what the signal is doing is with an oscilloscope.

This is what a known good looks like, it's a pretty low amplitude signal.