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2009 Toyota Venza

Recently noticed that when the front defrost mode is select (which sets fan to max and directs air to the windshield), the entire HVAC system shuts off (i.e. blower motor stopped, HVAC controls stopped working, HVAC screen went blank). Only way to restore HVAC that I've discovered is to turn the key off, then back on.

  • This HVAC shutdown is repeatable within 1-2 seconds any time the fan goes to max (i.e. selecting defrost, or manually setting the fan speed to max, or setting the automatic climate control to max hot or max cold) AND when the engine is ON.
  • If the key is ON but engine is OFF, the problem does not occur.
  • Turning the engine OFF, then key back ON restores HVAC system functionality.
  • If fan is on MAX, starting engine (key ON, engine ON) will cause HVAC system to shut down in 1-2 seconds.
  • There are no DTCs.

Diagnostic advice?

Two factors that may or may not be relevant, but which precede the observation of this issue:

  1. The blower motor was making some noise a few months ago. Sounded like a bad bearing and some fine copper colored dust was observed near the motor shaft. I lubricated the bearings as much as possible with mineral oil and reinstalled it. The noise has not returned so far and the fan works at all commanded speeds. Also note that I do not believe there is a resister module and that this fan works with PWM control.

  2. The alternator died and was replaced also a few months ago. The replacement is an aftermarket unit. A battery tester shows the charging system is ok, ripple is ok, battery is ok.

adatum
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1 Answers1

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This is just a shot in the dark, as I have no special knowledge of the Toyota Venza.

Access the blower motor and make sure it is spinning easily and freely by hand. If it's dragging due to a bad bearing, the current required to run it at max speed may be overloading the air conditioning module and forcing it to shut down. If the blower is not spinning freely, replace the blower motor.

If the blower spins freely, access the air conditioning module and give it a good long shot with a freezing spray, hitting the board components themselves if possible, not just the outer case. Then immediately turn the A/C to max and note how long it takes to shut down. If it still shuts down in 1-2 seconds, I give up and have no further suggestions. But if it runs significantly longer than 1-2 seconds, you may have a failing air conditioning module that needs to be replaced.

MTA
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