Gen 1 A/C issues

You've come to the right place - there are a bunch of threads with very useful information on the Gen 1 A/C system in this forum.

-Chap

 

When it starts at 80/80, 80% humidity and 80 F, I just take the 2010 with the electric A/C and don't worry about it. If even a little dryer, I'll use the 2003 with the windows rolled down. I just don't care for an engine driven A/C any more.

Bob Wilson

 

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!

ChapmanF recommends measure and set the factory spec clutch plate spacing; doing what the factory says is usually a good idea.... a new set of spacers is less than @10 but you need a micrometer to tell the spacers apart

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.

BTW, you don't need a micrometer to tell the three shims in the kit apart. They're all thin, yes, but 0.5 mm is still five times as thick as 0.1 mm, right?, and 0.3 mm is right in the middle, and you can feel and see the difference if you know to look for it. I only posted the micrometer photo in reply to another post that did PriusChat readers a disservice by saying they were all one size.

If you don't want to trial-and-error it, you should have a way to measure the old shims that come out with the pressure plate. Your most beat-up cheap caliper is adequate for that.

The one tool that does contribute a lot to success is a dial indicator. The reason is that new (flat!) clutch gap can be measured with a dial indicator or a simple feeler gauge, but on an old clutch the feeler gauge will read false and the dial indicator will always be right. I used to think of dial indicators as expensive, but there are indicators on eBay under $10 and sets with a mounting base around $20, and they'll do everything a DIYer needs for this job and a ton of others around the car (like checking brake rotor runout).

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