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Ask Ted Ritter Your Own Question
Ted Ritter
Ted Ritter, Toyota Master Tech
Category: Toyota
Satisfied Customers: 4378
Experience:  Toyota Master Tech, ASE Certified
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The AC isn't working on my 2000 Sienna I just received from

Customer Question

The AC isn't working on my 2000 Sienna I just received from a friend. The light doesn't turn on when you push the AC button and the compressor doesn't engage. They said when it went bad they got it checked out and that water had leaked down the roof somewhere and shorted something. I looked at what I think is the AC relay under and to the left of the steering wheel and bypassed that relay. Immediately the white/black wire behind the relay started smoking/melting. I think it had melted before as well. I also hot wired the compressor clutch to the battery for a split second and it turned on and sounded really loud. I've checked all pertinent fuses and the switch at the heater controls. I have everything torn down for easy access. What would make that white/black wire melt? How do I troubleshoot the AC system?
Submitted: 1 year ago.
Category: Toyota
Expert:  Ted Ritter replied 1 year ago.

Thanks for posting

It sounds like either the a/c clutch or the compressor is seizing up, this is causing the noise, if you have the compressor removed check to be sure the clutch is not burned out, if the clutch is ok it's most likely the compressor is seizing, the wire is melting due to excessive current drawn by the clutch which in turn can be caused by a seizing compressor.

Customer: replied 1 year ago.
Why doesn't it attempt to turn on? Why would that one random wire on the rear heater relay be the only place it shows overload? Is it possible a wire is shorted to ground somewhere and the compressor/clutch is fine? How do I test to narrow down the issue?
Customer: replied 1 year ago.
Also, behind the glove box I can see what I think is the evaporator. There is yellow conduit with two wires heading up towards it. Once it reaches the evaporator it has a coupling and goes inside the evaporator. Is that the thermistor? When I tested ohms on the two different prongs in the connector they were at 0 ohms. Does that mean its bad? Could that be the issue over all?
Customer: replied 1 year ago.
Or... is that something to do with the airbag?
Customer: replied 1 year ago.
Scratch the yellow conduit part of the question. I know that's the airbag. Here is the latest. The white/red wire on the connector to the compressor shows continuity to ground. The white/red wire on the connector to the thermistor shows continuity to ground. I can also see that wire disappearing up near the inside of the fender. Should that white/red wire have 0 ohms to ground? If not, have I found a short?
Expert:  Ted Ritter replied 1 year ago.

The white/red wire should not show zero ohms to ground, if it does it is shorted to ground, are there any fuses blown?

Customer: replied 1 year ago.
No fuses are blown.
Expert:  Ted Ritter replied 1 year ago.

Ok, I'll have to get back to you on that, I'll have to check a wiring diagram of the a/c system.

Customer: replied 1 year ago.
I've seen the diagram. That wire goes from the compressor to the thermistor and the amplifier.
Customer: replied 1 year ago.
I'll just look for the short on the run of wire between the thermistor and the junction and the junction and the compressor.
Customer: replied 1 year ago.
Here is another good image of the diagram.
Expert:  Ted Ritter replied 1 year ago.

Sorry for the delay in getting back to you, very busy lately.

It seems you're on the right track, try disconnecting the connector on the amplifier, if the short is still there then it's between those teo points, god luck, keep posted. Thanks, Ted.

Customer: replied 1 year ago.
I found it. The AC Amplifier is completely corroded and the prong for the white/red wire was shorted to the prong for the ground wire internally via the board. I ordered a replacement AC Amplifier. Next I will see if the compressor is bad as well or not. At worst, I'm thinking a new compressor and AC service once I get the new amplifier installed.