A/C sometimes won't start?

[Greedo51]

Sometimes when I start my yaris the A/C will not come on. This happens about once a month. It began occurring about 12 months ago. Some times the A/C will kick on minutes after starting the car, sometimes hours, sometimes the next day. I believe it also happened with the defrost in the winter. I made an appointment with my local toyota dealer when it last went out on me. The next day when I had the appointment the A/C started working. They checked it out and could find nothing wrong. They said it needed to be not working for the computer test to show an error. They said if it goes out again to rush it back up there and they would check for free. Every time it goes out I head towards the dealership, but the A/C comes back on before I get there. Does anyone have any idea what the problem could be??? I would GREATLY appreciate any insight.

[CTScott]

The AC Amplifier (ECU) has an input from the alternator that prevents it from trying to run when the engine is not. That connection or the alternator itself could possibly be the issue. It could also be an issue with the drive circuitry within the AC ECU that engages the electric clutch on the compressor

When the problem occurs, the fan works, but the A/C does not?

[Greedo51]

The fan will not run either.

[rsoaramud]

hello, i would like to ask if i need to change the compressor, my ac is running cold when the car is in idle mode but once the car rolling the ac shuts down for 1min and turns cold again, this happens every time i am in a stop light red (cold) green (blows hot air) but once the car is running continuesly the ac becomes good again. what seems to be the problem?

[comk4ver]

Mine does the same thing! You're right every now and then. Today is the first time that it's done on four days! It's sweltering here in California.
Sometimes when I start my yaris the A/C will not come on. This happens about once a month. It began occurring about 12 months ago. Some times the A/C will kick on minutes after starting the car, sometimes hours, sometimes the next day. I believe it also happened with the defrost in the winter. I made an appointment with my local toyota dealer when it last went out on me. The next day when I had the appointment the A/C started working. They checked it out and could find nothing wrong. They said it needed to be not working for the computer test to show an error. They said if it goes out again to rush it back up there and they would check for free. Every time it goes out I head towards the dealership, but the A/C comes back on before I get there. Does anyone have any idea what the problem could be??? I would GREATLY appreciate any insight.

[SirDigby]

first off. NEVER USE A/C PRO or any other cheap ass store product. next, you Toyota dealership sucks, and is full of retards. checking the computer for codes is nice if there is a problem with electronics, but what those morons need to do is hook the vehicle up to a set of gauges and watch your performance. I bet you have a slightly low charge and the pressure is dropping low enough to kick the safety switch on the system. same with the problem of running hot at a stop sign. when the engine turns faster, the compressor builds pressure and system resumes operation...