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I have a 2003 manual Toyota Yaris with a very strange A/C problem, which got me and the A/C shop baffled. History:

  1. Since I bought the car 8 years ago, it had a weird problem where the A/C compressor would not start working when starting the car after it had been parked in the sun for a few hours. Only after some 5 minutes it would suddenly kick in and start cooling.
  2. Recently, it also started cooling poorly (mostly on low RPMs), and the shop said the compressor is dead and needs replacing.

So, they replaced it with a brand new compressor. Both problems are now gone, but instead an even weirder and more annoying problem came up:

  • Whenever I reach a speed of ~50 Km/h and go over ~2500 RPM, the compressor would disengage and stop cooling completely.
  • This is not a problem with the TPS sensor, as releasing the gas pedal at high speed would not cause it start cooling again
  • If I shift out of gear at high speed and let the RPM fall to idle, it will start cooling even if still at high speed
  • I thought it might be a high coolant pressure problem, but just hitting the gas while parking in neutral does NOT cause the problem to appear. It will cool perfectly at neutral on 2500-3500 RPM. This only happens when the car is above some speed.

Any ideas? I can't even think what could cause this weird problem...

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  • Check who is shutting down the AC. Wrap a wire around a relay leg and feed it inside the cab. This lets you measure while driving. It sounds like a load management issue but i'm just spitballing here. It's common for the PCM to shut things down during high load conditions. If something is fooling it into thinking there is high load?
    – vini_i
    Jun 13 '17 at 9:38
  • @vini_i - that's exactly what the guy which replaced the compressor just suggested. He will put a bulb in the car fed by the compressor power line to see if it's a control problem.
    – Zohar Bar-Yehuda
    Jun 13 '17 at 10:34
  • Shot in the dark here...Check the cooling fan(s). To protect from overheating, some cars AC will not engage unless the fans are running. If the circuit is turning the fan off, a loose connection that is effected by airflow, or they are not functioning properly, could be an issue.
    – CharlieRB
    Jun 13 '17 at 11:36
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OK, 1 week later, this is the outcome (up to the level I could understand over phone conversations):

A/C shop replaced the new (Taiwanese) compressor with a different (Chinese) compressor. Problem persisted. They kind of gave up on it...

Went to the main Toyota shop, where they investigated it but couldn't find any control issue. Seems when the gas pedal is pressed firmly, the voltage to the compressor drops for a short period (maybe intended to give the engine more power), but when released to a cruise level, they saw the voltage returns to perfect but the compressor wasn't functioning.

Eventually, they replaced it to a third new compressor, this time a Japanese Denso one, and the problem is simply gone. My guess is that in the 2 other compressors, the compressor clutch wasn't able to lock at high RPMs, and therefore once the voltage had dropped, even momentarily, it would re-lock only when RPMs fell to idle.

The A/C shop refunded me for everything, and instead I paid only to the Toyota shop. This whole adventure cost me a small fortune (around a third of the car's value, prices at the Toyota shop are crazy...), but at least now I have a proper A/C :)

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  • 1
    +1. A good example of why it makes sense to buy original parts.
    – juhist
    Aug 21 '17 at 20:28

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