another blinking A/C light; advice kindly requested

I suggest that you need to take your car to a place that specializes in automotive air conditioning repair. The Classic Prius air conditioning system is of conventional design, with a belt-driven compressor.

One reason that the air conditioning will be intermittent is if there is moisture in the system. The moisture freezes up at the expansion valve orifice which stops the cooling cycle. After the blockage melts, the cooling action can resume.

If this is the case, then the existing refrigerant would be removed, the dryer replaced (which absorbs moisture), and the system placed on a vacuum pump to evacuate all residual moisture. Then new R-134a refrigerant would be charged and the system should be back to normal operation.

 

What happens if you don't wait a few minutes, does it continue to behave as if there is a fault? Have you tried asking for fault codes then?

-Chap

 

My guess is that the repair cost would be less than $600, but my guess doesn't count. What counts is the quotes you can obtain in your local area.

 

Asking for codes has to be done within five seconds of turning the key ON, so you have to briefly turn the key OFF in order to do it. I merely wondered whether you had tried asking for codes right away after the fault had been detected, without any minute-or-so wait, or only at some later time when you started the car up cold?

If you have a dial indicator or a friend who has one, I would certainly measure the travel of your clutch plate, even if you don't actually catch a code 22. Our cars are all old enough now to make that worth checking, and it's a super cheap fix. The specified travel is supposed to be 0.5 mm. Anything 0.35–0.65 is ok. Mine had worn to fully 1.34 mm (!!) before I started getting intermittent dropouts.

-Chap

 

Before attempting expensive solutions (taking to A/C repair place or dealer) may I suggest a DIY attempt?

Elder Gen I Prii A/C clutches are prone to slippage (and subsequent blinking A/C LED) due to (a) worn serpentine belt and (b) buildup of rust/debris between plates of the magnetic clutch.

So first: replace the serpentine belt. A new serpentine belt is less than $20 at most auto parts stores. Toyota wants $100 to replace it.

Requires removal of passenger front tire, removal of inner plastic splash shroud, and maybe 90 minutes in the driveway.

Secondly: partial disassemble the A/C magnetic clutch and clean the plates with isopropyl alcohol on a cloth (or more enthusiastically, with a bronze wire brush and Dremel tool) using procedure described in the instructions from THIS link:

Station's AutoBlog: Gen 1 Prius A/C Clutch Diagnostics and Replacement

This blogger describes a replacement procedure; I happen to disagree that the "grooves" in the clutch plate are wear marks. They looked machined to me, so I cleaned my clutch and EGADS! my previously intermittant A/C now works gangbusters!

If you are satisfied that the serpentine belt is NOT slipping and the clutch plates are clean and giving good mechanical connection, then it's time to suspect either the compressor itself or something else in the A/C system.

But read the linked blog entry in any case. It's an excellent DIY project.

 

No need to take off the passenger tire—just steer to the right, plenty of access to the compressor.

The groove business is a distraction, if you're looking at it thinking "oh, it's got grooves, but maybe the original had grooves, so it isn't worn, right?"

There's an excellent photo of a new pressure plate in station2station's blog post already linked. Scroll down to the big one that shows the old and new parts side by side. The new pressure plate is in the lower right corner. You can see that it is divided into two separate friction surfaces, with a gap between them that maybe you're calling a "groove", but except for that they are machined absolutely flat. And that's not what the worn one looks like. It never is.

And even though the surfaces wear grooves, you're right in a sense that the grooves don't matter. The two pieces still fit perfectly, because they wore the grooves into each other. The only thing that matters as they wear is the overall distance they have to travel to meet. That gap starts out at one-half millimeter from the factory. By the time it gets to be twice or three times the gap it should have, you're likely to see slippage.

When that happens, you spend ten minutes with the one dollar shim kit, restore the correct gap, and go on to solve other world problems.

Honestly, I've never checked how much more time you'd get out of a worn clutch by putting in the same effort as to fix the excess gap (pressure plate off, pressure plate back on), but without fixing it, instead putting in more work of solvent washing and/or Dremeling. It's useful to know that did something for you, and it may help another person who is sweating in the boondocks with no access to a shim kit, at least long enough to get to civilization and get one.

But honestly, there's nothing special about the Prius Gen 1 magnetic clutch, such things go back to 1954 Pontiacs. That would be sixty years for your repair idea here to have become widely known and practiced, and I'm not aware that it has. If the gap's too big and it slips, make the gap not too big, and it won't.

-Chap