Powered roof vent fan
A guided diagnosis for RV techs. Each step is a check, a reading or a question.
- Vent fan complaint? Fan-Tastic, MaxxAir and similar: a 12V fan, a lid motor or a manual crank, often a rain sensor and a thermostat. Expect: 12V at the fan, lid opens and closes fully
- Is the lid open? Many fans (Fan-Tastic included) have a lid switch: the fan will not run with the lid closed, by design.
- 12V at the fan's terminal block or board? Pull the inside garnish and meter the feed. Expect: 12 to 13.6 V
Causes and repairs
Lid closed, fan locked out
Normal. Open the lid and the fan runs.
Tools: none
Open the lid. If it runs only with the lid fully open, the lid switch may need adjusting.
Fan fuse or feed
The fan's fuse at the panel, an inline fuse at the fan, or a loose spade at the terminal block.
Tools: multimeter
Replace the fuse, tighten the terminals.
Lid switch, control or motor
With 12V in and the lid open, check the lid switch for continuity, then the speed switch or board output, then 12V at the motor. 12V at the motor and nothing: motor.
Tools: multimeter
Replace the part where the voltage stops.
Lid motor or linkage
Powered lids strip their gear or lose a limit. Manual cranks strip the worm gear.
Tools: hand tools
Replace the lid motor or crank assembly. Lubricate the lift arms.
Rain sensor
Dew or dirt on the sensor closes the lid on a dry day.
Tools: none
Clean the sensor. Replace it if it closes dry.
Thermostat setting or board
The fan's thermostat runs it when it is warm inside. A failed board runs it always.
Tools: none
Raise the set point or switch to manual. Replace the board if it ignores the controls.