I have a 1994 Toyota Camry 3000 V6. The heater blows hot air only when under exceleration. At a stop light or stop sign it blows cold air. At the same stop if you hold the brake harder and give it some gas it will blow hot air again. There doesn't apear to be any sign of a heater core leaking or the thermostat sticking.
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A.S.E. MASTER TECHNICIAN. TOYOTA SERVICE TRAINING, ADVANCED LEVEL ENGINE PERFORMANCE,CA SMOG, HYBRID