Hand dryer common faults and solutions

Symptom 1: When the hand is placed in the hot air outlet, no hot air is blown out — only cold air comes out.

Diagnosis and Repair: The presence of cold air indicates that the hair dryer's motor is functioning properly, and the infrared detection and control circuit is also working as expected. However, the absence of hot air suggests a problem with the heating element or its wiring. Upon inspection, it was found that the heater’s wiring was loose. After re-connecting the wires, the hair dryer began to blow hot air again, and the issue was resolved.

Symptom 2: After turning on the device, hot air starts blowing even without the hand being placed near the outlet.

Diagnosis and Repair: Initial checks showed that the thyristor was not broken down. However, there was a suspicion of internal leakage in the optocoupler’s photocoupler, specifically between pins 3 and 4. Replacing the faulty optocoupler restored normal operation, and the problem was fixed.

Symptom 3: When the hand is placed in the hot air outlet, no hot air is produced.

Diagnosis and Repair: A check of the fan and heater confirmed they were working normally. Further testing revealed that the thyristor’s gate had no trigger voltage. The control board was found to be outputting a rectangular wave signal, which suggested an issue with the optocoupler. Using a multimeter set to R×10, the resistance between pins 3 and 4 of the optocoupler was measured as infinite. In a normal optocoupler, the forward resistance should be several ohms, while the reverse resistance should be infinite. This indicated that the internal photoelectric tube was open, preventing the thyristor from receiving the necessary trigger voltage and thus failing to turn on. Replacing the optocoupler resolved the issue.