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Hi There, I'm Clayso a certified master automobile technician with 30 years of automotive repair and diagnostic experience.
From your description most likely the evaporator drain is clogged and not allowing the condensate to drain from the evaporator case. On the passenger side under the dash behind the carpet is the drain from the evaporator case to the body. Make sure this drain is clear, when the drain is clear there will be condensate now dripping on the ground at the passenger side behind the front wheel.
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The air flow through the evaporator case changes when the A/C is on AUTO the intake air is on recirculated air mode. Toyota issued a service bulletin in April 2014 concerning a clogged evaporator drain. The service bulletin is in the link below.
2008 Toyota Rav4 T-SB-0033-14
The TSB is mostly concerned about insects causing the blockage, but anything that could be drawn into the evaporator case through the recirculation vent can stop up the evaporator case drain. May also be a good time to check and or replace the cabin air filter.
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