Super weird Yaris 2003 A/C problem

[zoharby]

Brand new compressor (or at least what they told me, it looks shiny and new...).
We were able to trigger the problem on the lift at the shop:
Compressor stops cooling above 50Km/h (wheels spinning in air on lift on 3rd/4th/5th gear) and above 2500 RPM. Compressor is still getting power (they put a LED on the line which stayed on). Would only kick back in when RPMs fall back to ~1000.

Seems like a compressor clutch issue, but we were baffled as to why the wheel speed has anything to do with it.

* They tried putting another wire in parallel from the battery directly to the compressor, did not change anything.
* When they disconnected the compressor wire from the normal feed and connected it to the battery directly (i.e. instead of the normal feed, not in parallel) the problem did not occur.

They are now changing the compressor again, let's hope it solves it

[CoryM]

Originally Posted by zoharby

Compressor is still getting power (they put a LED on the line which stayed on).

Assuming that is true, you know it's not a control problem or electrical issue. So long as the compressor has power and ground and the clutch is locking, your a/c should be blowing cold. I would suggest the next step is to hook up the refrigerant pressure gauges and induce the problem. If you see the low pressure side going from normal PSI to vacuum and back, it's probably a blocked orifice. If your pressures are normal until it acts up, it's probably ice. Your dryer could be saturated with water, and/or the refrigerant is contaminated with water. This is my guess from thousands of miles away. If it is, replace the dryer and use NEW refrigerant.

With pressure gauges you can diagnose just about any pressure related issue. It's been too long since I did that stuff to remember it all.
Here is a chart that may be handy.

http://www.sanden.com/objects/SANDEN...OSIS_CHART.pdf

Cheers.

[zoharby]

Originally Posted by CoryM

Assuming that is true, you know it's not a control problem or electrical issue.

But when connecting the compressor directly to the battery (i.e. disconnected from car control completely), it doesn't happen.

My guess is that when it happens it receives a lower voltage (e.g. 3-5V) that is enough to power the LED but not enough for the the compressor clutch to lock.

After some more experiments, it does seem to be related to the throttle pedal, so maybe it is related to the throttle position sensor. If I give a quick stronger push on the gas pedal at neutral (but still far away from fully pressed) I seem to be able to trigger it at neutral. Or maybe related to the high pressure sensor.

The A/C guy gave up on it (he doesn't know enough about the electrical & control system...). I will head to the main Toyota shop next week and will ask them to hook a volt meter on the compressor line, maybe it will show the voltage dropping when this starts.

[CoryM]

OK. I read " Compressor is still getting power (they put a LED on the line which stayed on)" and figured that the compressor clutch was locked at that point. Did you see the compressor clutch disengage while it still had power going to it? If so (and I would be surprised if so), it's probably a low-current issue such as a bad driver or similar. If the clutch remains engaged when you lose cooling, it is not a control issue.

Esse10: Yes the condensor needs airflow. But I think we have that well covered since the issue occurs while driving at 50kph. I was just making the point that so long as the compressor is spinning, it is definitely not a control issue. If you are getting picky, you also missed a bunch of other mechanical things the a/c system needs to operate.

Cheers.

Originally Posted by zoharby

But when connecting the compressor directly to the battery (i.e. disconnected from car control completely), it doesn't happen.

My guess is that when it happens it receives a lower voltage (e.g. 3-5V) that is enough to power the LED but not enough for the the compressor clutch to lock.

After some more experiments, it does seem to be related to the throttle pedal, so maybe it is related to the throttle position sensor. If I give a quick stronger push on the gas pedal at neutral (but still far away from fully pressed) I seem to be able to trigger it at neutral. Or maybe related to the high pressure sensor.

The A/C guy gave up on it (he doesn't know enough about the electrical & control system...). I will head to the main Toyota shop next week and will ask them to hook a volt meter on the compressor line, maybe it will show the voltage dropping when this starts.

[esse10]

Originally Posted by CoryM

Assuming that is true, you know it's not a control problem or electrical issue. So long as the compressor has power and ground and the clutch is locking, your a/c should be blowing cold. I would suggest the next step is to hook up the refrigerant pressure gauges and induce the problem. If you see the low pressure side going from normal PSI to vacuum and back, it's probably a blocked orifice. If your pressures are normal until it acts up, it's probably ice. Your dryer could be saturated with water, and/or the refrigerant is contaminated with water. This is my guess from thousands of miles away. If it is, replace the dryer and use NEW refrigerant.

With pressure gauges you can diagnose just about any pressure related issue. It's been too long since I did that stuff to remember it all.
Here is a chart that may be handy.

http://www.sanden.com/objects/SANDEN...OSIS_CHART.pdf

Cheers.

nope, not all true . the condenser has to have ambient temperature airflow through it or you'll never get cold air out of the dash vents.